Upgrading and Repairing PCs, Eleventh Edition

Upgrading and Repairing PCs, Eleventh Edition
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Page i
Contents at a Glance
Introduction xxii
1 Personal Computer Background
1
2 PC Components, Features, and
System Design 17
3 Microprocessor Types and Specifications
4 Motherboards and Buses
5 BIOS
UPGRADING
AND
REPAIRING PCS,
Eleventh Edition
35
203
345
6 Memory
413
7 The IDE Interface
503
8 The SCSI Interface
529
9 Magnetic Storage
Principles 567
10 Hard Disk Storage
583
11 Floppy Disk Storage
639
12 High-Capacity Removable Storage
13 Optical Storage
671
705
14 Physical Drive Installation and
Configuration 771
15 Video Hardware
803
16 Serial, Parallel, and Other I/O Interfaces
17 Input Devices
899
18 Internet Connectivity
19 Local Area Networking
20 Audio Hardware
949
995
1045
21 Power Supply and Chassis/Case
22 Printers and Scanners
23 Portable PCs
Scott Mueller
1085
1143
1205
24 Building or Upgrading Systems
1251
25 PC Diagnostics, Testing, and
Maintenance 1287
26 Operating System Software and
Troubleshooting 1337
27 File Systems and Data Recovery
28 A Final Word
1423
A Web Site List
1447
B Glossary
1379
1451
C Making the Most Of PartitionMagic and
Drive Image 1529
Index
201 West 103rd Street,
Indianapolis, Indiana 46290
1537
871
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Upgrading and Repairing PCs,
11th Edition
Copyright © 1999 by Que® Corporation
Associate Publisher
Jim Minatel
Acquisitions Editor
Jill Byus
All rights reserved. No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any
means, electronic, mechanical, photocopying, recording, or
otherwise, without written permission from the publisher.
No patent liability is assumed with respect to the use of the
information contained herein. Although every precaution
has been taken in the preparation of this book, the publisher and author assume no responsibility for errors or
omissions. Neither is any liability assumed for damages
resulting from the use of the information contained herein.
Senior Development Editor
International Standard Book Number: 0-7897-1903-7
Managing Editor
Library of Congress Catalog Card Number: 98-87630
Printed in the United States of America
00
99
4
3
Technical Editors
Mark Soper
Jeff Sloan
Joe Curley
Anthony Armstrong
Doug Klippert
Pete Lenges
Karen Weinstein
Kent Easley
Ariel Silverstone
Lisa Wilson
Project Editor
Natalie Harris
Copy Editors
First Printing: August 1999
01
Rick Kughen
2
Trademarks
All terms mentioned in this book that are known to be
trademarks or service marks have been appropriately capitalized. Que cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as
affecting the validity of any trademark or service mark.
Warning and Disclaimer
Every effort has been made to make this book as complete
and accurate as possible, but no warranty or fitness is
implied. The information provided is on an as is basis. The
author and the publisher shall have neither liability nor
responsibility to any person or entity with respect to any
loss or damages arising from the information contained in
this book or from the use of the CD or programs accompanying it.
Pamela Woolf
Michael Dietsch
JoAnna Kremer
Kelly Talbot
Kelli Brooks
Lisa Lord
Indexer
Kevin Kent
Proofreader
Benjamin Berg
Software Development
Specialist
Brandon Penticuff
Interior Design
Glenn Larsen
Cover Design
Karen Ruggles
Layout Technician
Mark Walchle
Formatter
Katie Robinson
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Contents
Introduction
xxii
3 Microprocessor Types and
Specifications 35
1 Personal Computer
Background 1
Microprocessors
Pre-PC Microprocessor History
Computer History—Before Personal
Computers 2
Timeline 2
Mechanical Calculators 5
The First Mechanical Computer
Electronic Computers 7
5
Modern Computers 7
From Tubes to Transistors 8
Integrated Circuits 9
The First Microprocessor 9
Personal Computer History 11
Birth of the Personal Computer
The IBM Personal Computer
The PC Industry 18 Years Later
12
14
11
2 PC Components, Features,
and System Design 17
What Is a PC? 18
Who Controls PC Software? 18
Who Controls PC Hardware? 21
PC 9x Specifications 25
26
System Components 29
Motherboard 30
Processor 31
Memory (RAM) 31
Case (Chassis) 31
Power Supply 32
Floppy Disk Drive 32
Hard Disk Drive 32
CD-ROM Drive 33
Keyboard 33
Mouse 33
Video Card 33
Monitor (Display) 34
36
Processor Specifications 39
Processor Speed Ratings 42
Processor Speeds and Markings Versus
Motherboard Speed 45
Data Bus 50
Internal Registers (Internal Data
Bus) 51
Address Bus 52
Internal Level 1 (L1) Cache 53
Level 2 (L2) Cache 55
Cache Organization 56
Processor Modes 58
SMM (Power Management)
Superscalar Execution
MMX Technology
System Types
36
61
61
62
SSE (Streaming SIMD Extensions)
Dynamic Execution 64
Multiple Branch Prediction
Data Flow Analysis 64
Speculative Execution 65
63
64
Dual Independent Bus (DIB) Arc
hitecture 65
Processor Manufacturing
PGA Chip Packaging
66
70
Single Edge Contact (SEC) and Single Edge
Processor (SEP) Packaging 71
Processor Sockets 74
Socket 1 75
Socket 2 76
Socket 3 78
Socket 4 79
Socket 5 80
Socket 6 82
Socket 7 (and Super7)
Socket 8 84
Socket PGA-370 85
82
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Zero Insertion Force (ZIF) Sockets
P5 (586) Fifth-Generation Processors
Pentium Processors 129
First-Generation Pentium
Processor 133
Second-Generation Pentium
Processor 134
Pentium-MMX Processors 137
Pentium Defects 138
Testing for the FPU Bug 139
Power Management Bugs 140
Pentium Processor Models and
Steppings 141
AMD-K5 149
86
Processor Slots 87
Slot 1 87
Slot 2 (SC330) 90
CPU Operating Voltages
91
Heat and Cooling Problems
Heat Sinks 94
93
Math Coprocessors (Floating-Point
Units) 97
Processor Bugs
100
Processor Update Feature
Intel Processor Codenames
100
102
Pseudo Fifth-Generation Processors 150
IDT Centaur C6 Winchip 150
Intel-Compatible Processors (AMD and
Cyrix) 103
AMD Processors 103
Cyrix 105
IDT Winchip 106
P-Ratings 107
P1 (086) First-Generation Processors 108
8088 and 8086 Processors 108
80186 and 80188 Processors 109
8087 Coprocessor 109
P2 (286) Second-Generation Processors
286 Processors 109
80287 Coprocessor 111
286 Processor Problems 111
P3 (386) Third-Generation Processors
386 Processors 112
386DX Processors 113
386SX Processors 113
386SL Processors 114
80387 Coprocessor 114
Weitek Coprocessors 115
80386 Bugs 115
129
109
112
P4 (486) Fourth-Generation Processors 117
486 Processors 117
486DX Processors 120
486SL 121
486SX 122
487SX 123
DX2/OverDrive and DX4
Processors 124
Pentium OverDrive for 486SX2 and
DX2 Systems 126
”Vacancy”—Secondary OverDrive
Sockets 126
80487 Upgrade 127
AMD 486 (5x86) 127
Cyrix/TI 486 128
Intel P6 (686) Sixth-Generation
Processors 151
Pentium Pro Processors 154
Pentium II Processors 162
Celeron 174
Pentium III 181
Pentium II/III Xeon 184
Pentium III Future 187
Other Sixth-Generation Processors 187
Nexgen Nx586 187
AMD-K6 Series 188
3DNow 191
AMD-K7 192
Cyrix MediaGX 192
Cyrix/IBM 6x86 (M1) and 6x86MX
(MII) 193
P7 (786) Seventh-Generation
Processors 194
Merced 195
Processor Upgrades 197
OverDrive Processors 198
OverDrive Processor Installation
OverDrive Compatibility
Problems 199
Processor Benchmarks 200
Processor Troubleshooting Techniques
4 Motherboards and
Buses 203
Motherboard Form Factors
Baby-AT 205
Full-Size AT 209
LPX 210
ATX 214
Micro-ATX 218
Flex-ATX 220
204
198
201
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NLX 222
WTX 226
Proprietary Designs 230
Backplane Systems 231
Motherboard Components
Processor Sockets/Slots
Chipsets
v
System Resources 311
Interrupts (IRQs) 312
DMA Channels 320
I/O Port Addresses 322
234
234
235
Intel Chipsets 237
Intel Chipset Model Numbers
Intel’s Early 386/486 Chipsets
238
240
Fifth-Generation (P5 Pentium Class)
Chipsets 241
Intel 430LX (Mercury) 242
Intel 430NX (Neptune) 242
Intel 430FX (Triton) 243
Intel 430HX (Triton II) 244
Intel 430VX (Triton III) 246
Intel 430TX 246
Third-Party (Non-Intel) P5 Pentium
Class Chipsets 247
Sixth-Generation (P6 Pentium Pro/Pentium
II/III Class) Chipsets 252
Intel 450KX/GX (Orion
Workstation/Server) 256
Intel 440FX (Natoma) 256
Intel 440LX 257
Intel 440EX 257
Intel 440BX 258
Intel 440ZX and 440ZX-66 259
Intel 440GX 260
Intel 450NX 260
Intel 810 261
Third-Party (non-Intel) P6 Class
Chipsets 265
Super I/O Chips 267
Motherboard CMOS RAM
Addresses 268
Motherboard Interface
Connectors 272
System Bus Functions and Features
The Processor Bus 277
The Memory Bus 281
The Need for Expansion Slots
Contents
276
281
Types of I/O Buses 282
The ISA Bus 283
The Micro Channel Bus 288
The EISA Bus 289
Local Buses 292
VESA Local Bus 294
The PCI Bus 299
Accelerated Graphics Port (AGP)
310
Resolving Resource Conflicts 326
Resolving Conflicts Manually 326
Using a System-Configuration
Template 328
Heading Off Problems: Special
Boards 332
Plug-and-Play Systems 336
Knowing What to Look For (Selection
Criteria) 338
Documentation 342
Using Correct Speed-Rated Parts 342
5 BIOS
345
BIOS Basics
346
BIOS Hardware/Software
347
Motherboard BIOS 349
ROM Hardware 350
ROM Shadowing 352
Mask ROM 353
PROM 353
EPROM 355
EEPROM/Flash ROM 356
ROM BIOS Manufacturers 357
Upgrading the BIOS 363
Where to Get Your BIOS Update 364
Determining Your BIOS Version 365
Backing Up Your BIOS’s CMOS
Settings 365
Keyboard-Controller Chips 366
Motherboard CMOS RAM
Addresses 371
Replacing a BIOS ROM 375
CMOS Setting Specifications 375
Running or Accessing the CMOS Setup
Program 375
BIOS Setup Menus 376
Maintenance Menu 377
Main Menu 377
Advanced Menu 379
Security Menu 390
Power Management Menu 391
Boot Menu (Boot Sequence,
Order) 394
Exit Menu 395
Additional BIOS Setup Features 396
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Year 2000 BIOS Issues
Award 399
AMI 399
Phoenix 400
397
Plug-and-Play BIOS 400
PnP Device IDs 401
Initializing a PnP Device
Preventing ROM BIOS Memory
Conflicts and Overlap 495
ROM Shadowing 496
Total Installed Memory Versus Total
Usable Memory 497
Adapter Memory Configuration and
Optimization 499
408
BIOS Error Messages 409
General BIOS Boot Text Error
Messages 410
6 Memory
Memory Basics
ROM
DRAM
7 The IDE Interface
Precursors to IDE 504
The ST-506/412 Interface
The ESDI Interface 507
413
414
The IDE Interface
416
IDE Origins
418
Cache Memory: SRAM
503
An Overview of the IDE Interface
RAM Memory Speeds 424
Fast Page Mode (FPM) DRAM 426
EDO (Extended Data Out) RAM 427
Burst EDO 428
SDRAM 428
Future DRAM Memory Technologies
RDRAM 429
DDR SDRAM 435
429
Physical RAM Memory 435
SIMMs and DIMMs 437
SIMM Pinouts 442
DIMM Pinouts 446
Physical RAM Capacity and
Organization 449
Memory Banks 451
RAM Chip Speed 453
Gold Versus Tin 453
Parity and ECC 457
Installing RAM Upgrades 465
Upgrade Options and Strategies 465
Selecting and Installing Motherboard
Memory with Chips, SIMMs, or
DIMMs 466
Replacing SIMMS and DIMMs with
Higher Capacity 467
Adding Adapter Boards 467
Installing Memory 468
Troubleshooting Memory 472
Memory Defect Isolation
Procedures 475
The System Logical Memory Layout 477
Conventional (Base) Memory 481
Upper Memory Area (UMA) 481
Extended Memory 494
ATA IDE
505
509
510
IDE Bus Versions
419
504
511
512
ATA Standards
513
ATA-1 (AT Attachment Interface for Disk
Drives) 513
ATA I/O Connector 514
ATA I/O Cable 516
ATA Signals 516
Dual-Drive Configurations 517
ATA Commands 519
ATA-2 (AT Attachment Interface with
Extensions) 520
ATA-3 (AT Attachment 3 Interface) 520
Increased Drive Capacity 521
Faster Data Transfer 523
DMA Transfer Modes 524
ATAPI (ATA Packet Interface) 525
ATA/ATAPI-4 (AT Attachment 4 with Packet
Interface Extension) 526
ATA/ATAPI-5 (AT Attachment 5 with Packet
Interface) 526
Obsolete IDE Versions 527
XT-Bus (8-bit) IDE 528
MCA IDE 528
8 The SCSI Interface
529
Small Computer System Interface (SCSI)
530
ANSI SCSI Standards
SCSI-1 and SCSI-2
532
537
SCSI-3 538
Fast and Fast-Wide SCSI 539
Fast-20 (Ultra) SCSI 539
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10 Hard Disk Storage
Fast-40 (Ultra2) SCSI 539
Fast-80 SCSI 540
Wide SCSI 540
Fiber Channel SCSI 540
Termination 540
Command Queuing 540
New Commands 540
SCSI Cables and Connectors
Definition of a Hard Disk
Hard Drive Advancements
Areal Density
541
SCSI Cable and Connector Pinouts
Single-Ended SCSI Cables and
Connectors 544
Differential SCSI Signals 547
Expanders 548
Termination 548
543
SCSI Drive Configuration 549
Start On Command (Delayed Start)
553
SCSI Parity 554
Terminator Power 554
SCSI Synchronous Negotiation 554
Plug-and-Play (PnP) SCSI
555
SCSI Configuration Troubleshooting
556
SCSI Versus IDE 557
SCSI Hard Disk Evolution and
Construction 558
Performance 564
SCSI Versus IDE: Advantages and
Limitations 564
Recommended SCSI Host
Adapters 565
9 Magnetic Storage
Principles 567
Magnetic Storage
583
584
585
585
Hard Disk Drive Operation 586
The Ultimate Hard Disk Drive
Analogy 589
Tracks and Sectors 591
Disk Formatting 594
Basic Hard Disk Drive Components 599
Hard Disk Platters (Disks) 600
Recording Media 601
Read/Write Heads 603
Read/Write Head Designs 604
Head Sliders 607
Head Actuator Mechanisms 608
Air Filters 618
Hard Disk Temperature
Acclimation 620
Spindle Motors 621
Logic Boards 621
Cables and Connectors 622
Configuration Items 623
The Faceplate or Bezel 623
Hard Disk Features 624
Reliability 624
Performance 627
Shock Mounting 636
Cost 636
Capacity 636
Specific Recommendations
11 Floppy Disk Storage
568
Floppy Disk Drives
History of Magnetic Storage
568
How Magnetic Fields Are Used to Store
Data 569
Magneto-Resistive (MR) Heads
574
Data Encoding Schemes 575
FM Encoding 577
MFM Encoding 577
RLL Encoding 578
Encoding Scheme Comparisons
579
PRML (Partial-Response, MaximumLikelihood) Decoders 581
Capacity Measurements
vii
Contents
581
638
639
640
Drive Components 640
Read/Write Heads 640
The Head Actuator 643
The Spindle Motor 644
Circuit Boards 645
The Controller 645
The Faceplate 646
Connectors 646
The Floppy Disk Drive Cable
647
Disk Physical Specifications and
Operation 649
How the Operating System Uses
a Disk 650
Cylinders 651
Clusters or Allocation Units 651
Diskette Changeline 652
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Types of Floppy Disk Drives 653
The 1.44MB 3 1/2-Inch Drive 654
The 2.88MB 3 1/2-Inch Drive 654
The 720KB 3 1/2-Inch Drive 655
The 1.2MB 5 1/4-Inch Drive 656
The 360KB 5 1/4-Inch Drive 657
Analyzing Floppy Disk Construction 657
Floppy Disk Media Types and
Specifications 660
Caring for and Handling Floppy Disks
and Drives 661
Airport X-ray Machines and Metal
Detectors 662
Drive-Installation Procedures
663
Troubleshooting Floppy Drives 664
Common Floppy Drive Error
Messages—Causes and
Solutions 665
Repairing Floppy Disk Drives 666
Cleaning Floppy Disk Drives 667
Aligning Floppy Disk Drives 668
12 High-Capacity Removable
Storage 671
Why Use Removable Drives?
672
Types of Removable Media Drives 673
High-Capacity Floptical Drives 674
21MB Floptical Drives 674
LS-120 (120MB) SuperDisk Drives 675
Bernoulli Drives 676
Zip Drives 676
Jaz Drives 679
SyQuest Drives 680
Removable Drive Letter Assignments
Comparing Removable Drives
681
683
Tape Drives 685
The Origins of Tape Backup
Standards 686
The QIC Standards 687
Other High-Capacity Tape Drive
Standards 692
Choosing a Tape Backup Drive 696
Tape Drive Installation Issues 698
Tape Drive Backup Software 700
Tape Drive Troubleshooting 701
Tape Retensioning 703
13 Optical Storage
705
What Is a CD-ROM? 706
CDs: A Brief History 706
CD-ROM Technology 707
TrueX/MultiBeam Technology
Inside Data CDs 711
709
What Types of Drives Are Available? 713
CD-ROM Drive Specifications 714
Interface 721
Loading Mechanism 725
Other Drive Features 727
CD-ROM Disc and Drive Formats 728
Data Standard: ISO 9660 730
High Sierra Format 730
CD-DA (Digital Audio) 731
CD-ROM XA or Extended
Architecture 731
Mixed-Mode CDs 734
PhotoCD 735
Writable CD-ROM Drives 738
CD-R 738
How to Reliably Make CD-Rs 742
CD-R Software 746
Creating Music CDs 747
Creating Digital Photo Albums 748
Creating a Rescue CD 748
Multiple Session CD-R Drives 748
CD-RW 749
DVD (Digital Versatile Disc) 751
DVD History 751
DVD Specifications 751
Adding a DVD Drive to Your
System 753
DVD Standards 754
DVD Standards 755
CD-ROM Software on Your PC 756
DOS SCSI Adapter Driver 757
DOS CD-ROM Device Driver 757
MSCDEX: Adding CDs to DOS 758
Loading CD-ROM Drivers 759
CD-ROM in Microsoft
Windows 3.x 760
Optical Drives in Windows 9x and
Windows NT 4.0 760
MS-DOS Drivers and Windows 9x 761
Creating a Bootable Disk with CD-ROM
Support 762
Making a Bootable CD-ROM for
Emergencies 763
Files Needed for a Bootable CD
764
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Caring for Optical Media
767
Troubleshooting Optical Drives 768
Failure Reading a CD 768
Failure to Read CD-R, CD-RW Disks in
CD-ROM or DVD Drive 768
IDE/ATAPI CD-ROM Drive Runs
Slowly 768
Poor Results When Writing to CD-R
Media 769
Trouble Reading CD-RW Disks on CDROM 769
Trouble Reading CD-R Disks on DVD
Drive 769
Trouble Making Bootable CDs 769
14 Physical Drive Installation
and Configuration 771
Hard Disk Installation Procedures 772
Drive Configuration 773
Host Adapter Configuration 773
Physical Installation 775
Hard Drive Physical Installation—Step by
Step 776
System Configuration 778
Formatting 779
Drive Partitioning with FDISK 782
Drive Partitioning with Partition
Magic 786
High-Level (Operating System)
Formatting 787
FDISK and FORMAT Limitations 788
Replacing an Existing Drive 789
Drive Migration for MS-DOS
Users 790
Drive Migration for Windows 9x
Users 790
Hard Disk Drive Troubleshooting and
Repair 791
Testing a Drive 792
Installing an Optical Drive 792
Avoiding Conflict: Get Your Cards in
Order 793
Drive Configuration 793
External (SCSI) Drive Hook-Up 795
Internal Drive Installation 796
Ribbon Cable and Card Edge
Connector 796
SCSI Chains: Internal, External, or Both
798
Floppy Drive Installation Procedures
801
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Tape Drive Installation Issues 801
Internal Installation 802
External Installation 802
15 Video Hardware
803
Video Display Technologies
CRT Monitors
805
LCD Displays
806
Flat-Panel LCD Displays
804
808
Monitor Selection Criteria 810
Monochrome Versus Color 811
The Right Size 811
Monitor Resolution 813
Dot Pitch 815
Image Brightness and Contrast (LCD
Panels) 815
Interlaced Versus Noninterlaced 815
Energy and Safety 816
Emissions 818
Frequencies 819
Refresh Rates 819
Horizontal Frequency 822
Controls 822
Environment 823
Testing a Display 823
Video Display Adapters 824
Obsolete Display Adapters 825
VGA Adapters and Displays 825
XGA and XGA-2 827
Super VGA (SVGA) 828
VESA SVGA Standards 829
Video Adapter Components 831
High-Speed Video RAM Solutions—
Older Types 837
Current High-Speed Video RAM
Solutions 838
Emerging High-Speed Video RAM
Solutions 838
The Digital-to-Analog Converter (RAMDAC) 839
The Bus 839
AGP Speeds 841
The Video Driver 842
Video Cards for Multimedia 844
Video Feature Connectors (VFC) 844
VESA Video Interface Port (VESA
VIP) 845
Video Output Devices 845
Still-Image Video Capture Cards 846
Multiple Monitors 846
Desktop Video (DTV) Boards 847
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3D Graphics Accelerators 851
Common 3D Techniques 853
Advanced 3D Techniques 854
APIs (Application Programming
Interface) 856
Microsoft DirectX 856
Troubleshooting DirectX 859
3D Chipsets 859
USB and 1394 (i.Link) FireWire—Serial and
Parallel Port Replacements 891
USB (Universal Serial Bus) 892
IEEE-1394 (Also Called i.Link or
FireWire) 896
17 Input Devices
Upgrading or Replacing Your Video
Card 862
Video Card Memory 864
TV Tuner and Video Capture
Upgrades 865
Warranty and Support 865
Video Card Benchmarks 865
Comparing Video Cards with the Same
Chipset 866
Adapter and Display Troubleshooting 867
Troubleshooting Monitors 869
Troubleshooting Video Cards and
Drivers 870
16 Serial, Parallel, and Other
I/O Interfaces 871
Introduction to I/O Ports
872
899
Keyboards 900
Enhanced 101-Key (or 102-Key)
Keyboard 900
104-Key (Windows 95/98
Keyboard) 902
Portable Keyboards 904
Compatibility 905
Num Lock 906
Keyboard Technology 907
Keyswitch Design 907
The Keyboard Interface 910
Typematic Functions 911
Keyboard Key Numbers and Scan
Codes 914
International Keyboard Layouts 919
Keyboard/Mouse Interface
Connectors 920
USB Keyboards and Mice 922
Keyboards with Special Features 922
Serial Ports 872
UARTs 876
Keyboard Troubleshooting and Repair
926
High-Speed Serial Ports (ESP and Super
ESP) 878
Disassembly Procedures and Cautions
Cleaning a Keyboard 929
Replacement Keyboards 930
928
Serial Port Configuration
879
Testing Serial Ports 880
Microsoft Diagnostics (MSD) 880
Troubleshooting I/O Ports in
Windows 881
Advanced Diagnostics Using Loopback
Testing 882
Parallel Ports
883
IEEE 1284 Parallel Port Standard 884
Standard Parallel Ports (SPP) 885
Bidirectional (8-bit) Parallel Ports 886
Enhanced Parallel Port (EPP) 886
Enhanced Capabilities Port (ECP) 887
Upgrading to EPP/ECP Parallel Ports
Parallel Port Configuration
Testing Parallel Ports
890
890
18 Internet Connectivity
888
934
949
Relating Internet and LAN
Connectivity 950
Asynchronous Modems
888
Linking Systems with Parallel Ports
Parallel to SCSI Converters
887
Pointing Devices 932
Pointing Device Interface Types
Mouse Troubleshooting 937
Microsoft IntelliMouse/IBM
Scrollpoint 940
TrackPoint II/III 941
Glidepoint/Track Pads 945
Running Windows Without a
Mouse 946
Future Pointing Devices 948
950
Modem Standards 952
Modulation Standards 956
Error-Correction Protocols 960
Data-Compression Standards 961
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Proprietary Standards 962
Fax Modem Standards 964
56KB Modems 965
Modem Recommendations 970
Integrated Services Digital Network
(ISDN) 972
What Does ISDN Really Mean for
Computer Users? 972
How ISDN Works 973
Benefits of ISDN for Internet
Access 975
Always on with Dynamic ISDN 976
ISDN Hardware 976
Leased Lines 977
T-1 and T-3 Connections
977
CATV Networks 978
Connecting to the Internet with a
“Cable Modem” 978
CATV Bandwidth 979
CATV Security 980
CATV Performance 981
DirecPC—Internet Connectivity via
Satellite 981
How DirecPC Works 981
DirecPC Requirements 982
Installing DirecPC 982
Purchasing DirecPC 983
DirecPC’s FAP—Brakes on High-Speed
Downloading? 983
Technical Problems and Solutions 983
Real-World Performance 984
DSL (Digital Subscriber Line) 985
Who Can Use DSL—and Who
Can’t 985
Major Types of DSL 985
DSL Pricing 987
Time Versus Access 987
Comparing High-Speed Internet
Access 988
Sharing Your High-Speed Internet Access
over a LAN—Safely 988
Modem Troubleshooting 990
Modem Fails to Dial 990
Computer Locks Up After Installing
Internal Modem 991
Computer Can’t Detect External
Modem 992
xi
Contents
19 Local Area Networking
995
Local Area Networks 996
Client/Server Versus Peer-to-Peer
997
Packet Switching Versus Circuit
Switching 999
The Networking Stack
1000
The OSI Reference Model 1000
Data Encapsulation 1003
LAN Hardware Components 1004
Client PCs 1005
Servers 1005
Network Interface Adapters 1009
Bus Type 1011
Cables and Connectors 1014
Data Link Layer Protocols
ARCnet 1023
Ethernet 1023
Token Ring 1024
1023
High-Speed Networking
Technologies 1026
Fiber Distributed Data Interface 1026
100Mbps Ethernet 1027
Asynchronous Transfer Mode 1029
Upper-Layer Protocols 1029
Building a Peer-to-Peer Network 1030
Peer-to-Peer Networking
Hardware 1030
Peer-to-Peer Solutions via Dial-Up
Networking 1031
Network Client Software 1032
Configuring Your Network
Software 1032
Setting Up Users, Groups, or
Resources 1033
TCP/IP 1035
How TCP/IP Differs on LANs Versus
Dial-Up Networking 1037
IPX 1037
NetBEUI 1038
Direct Cable Connections 1038
Null Modem Cables 1039
Direct Connect Software 1039
Wireless Direct Cable
Connection 1040
Direct Cable Connection (and
Interlink) Tricks 1040
Faster Direct Cable Connections
1041
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Troubleshooting Network Software
Setup 1041
Troubleshooting Networks in Use
Troubleshooting TCP/IP
1042
1042
Speakers
Troubleshooting Direct Cable
Connections 1043
20 Audio Hardware
Audio Adapter Concepts and Terms
The Nature of Sound 1063
Game Standards 1063
Frequency Response 1064
Sampling 1064
8-Bit Versus 16-Bit 1065
1082
Microphones
1084
21 Power Supply and
Chassis/Case 1085
1045
Audio Adapter Applications 1046
Games 1048
Multimedia 1048
Sound Files 1050
Audio Compression 1050
MIDI Files 1051
Presentations 1055
Recording 1056
Voice Annotation 1057
Voice Recognition 1057
Conferencing 1060
Proofreading 1060
Audio CDs 1060
Sound Mixer 1061
Is an Audio Adapter Necessary?
Troubleshooting Sound Card
Problems 1076
Hardware (Resource) Conflicts 1076
Other Sound Card Problems 1079
Considering the Importance of the Power
Supply 1086
Power Supply Function and
Operation 1086
Signal Functions 1086
1061
1062
Audio Adapter Features 1066
Connectors 1066
Volume Control 1068
Synthesis 1068
Data Compression 1069
Multipurpose Digital Signal
Processors 1070
CD-ROM Connectors 1070
Sound Drivers 1071
Choosing an Audio Adapter 1071
Consumer or Producer? 1071
Compatibility 1072
Bundled Software 1073
Audio Adapter Installation
(Overview) 1073
Installing the Sound Card (Detailed
Procedure) 1074
Using Your Stereo Instead of
Speakers 1075
Power Supply Form Factors 1088
PC/XT Style 1090
AT/Desk Style 1091
AT/Tower Style 1092
Baby-AT Style 1093
LPX Style 1094
ATX Style 1095
NLX Style 1098
SFX Style (Micro-ATX
Motherboards) 1099
Power Supply Connectors 1102
ATX Optional Power Connector 1105
Power Switch Connectors 1106
Disk Drive Power Connectors 1108
Physical Connector Part
Numbers 1109
The Power_Good Signal 1109
Power Supply Loading
Power-Supply Ratings
1110
1112
Power-Supply Specifications
1114
Power-Supply Certifications
1116
Power-Use Calculations
1117
Power Off When Not in Use
1120
Power Management 1122
Energy Star Systems 1122
Advanced Power Management 1122
Advanced Configuration and Power
Interface (ACPI) 1123
Power Supply Troubleshooting 1124
Overloaded Power Supplies 1126
Inadequate Cooling 1126
Using Digital Multi-Meters 1127
Specialized Test Equipment 1130
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Repairing the Power Supply
1131
Obtaining Replacement Units 1132
Deciding on a Power Supply 1132
Sources for Replacement Power
Supplies 1133
Using Power-Protection Systems 1134
Surge Suppressors (Protectors) 1136
Phone Line Surge Protectors 1137
Line Conditioners 1137
Backup Power 1137
RTC/NVRAM Batteries (CMOS
Chips) 1140
22 Printers and Scanners
1143
The Evolution of Printing and Scanning
Technology 1144
Printer Technology 1144
Print Resolution 1145
Page Description Languages
(PDL) 1147
Escape Codes 1152
Host-Based/GDI 1152
Printer Memory 1153
Fonts 1155
Printer Drivers 1157
How Printers Operate 1158
Laser Printers 1158
LED Page Printers 1165
Inkjet Printers 1166
Portable Printers 1167
Dot-Matrix Printers 1168
Color Printing 1168
Color Inkjet Printers 1171
Color Laser Printers 1171
Dye Sublimation Printers 1172
Thermal Wax Transfer Printers 1172
Thermal Fusion Printers 1173
Choosing a Printer Type 1173
How Many Printers? 1173
Combination Devices 1174
Print Speed 1175
Paper Types 1176
Cost of Consumables 1177
Installing Printer Support 1178
DOS Drivers 1178
Windows Drivers 1179
Printer Sharing via a Network
Print Sharing via Switchboxes
Other Options for Sharing
Printers 1185
Support for Other Operating
Systems 1185
Preventative Maintenance 1186
Laser and Inkjet Printers 1186
Dot-Matrix Printers 1187
Choosing the Best Paper 1187
Common Printing Problems 1188
Printer Hardware Problems 1188
Connection Problems 1190
Driver Problems 1191
Application Problems 1192
Scanners 1192
The Hand Scanner 1193
Sheetfed Scanners—”Faxing” Without
the Fax 1194
Flatbed Scanners 1195
Interfacing the Flatbed Scanner 1196
Slide Scanners 1197
Photo Scanners 1198
Drum Scanners 1198
TWAIN 1199
ISIS (Image and Scanner Interface
Specification) 1200
Getting the Most from Your Scanner’s
Hardware Configuration 1200
Scanner Troubleshooting 1201
Scanner Fails to Scan 1201
Can’t Detect Scanner (SCSI or
Parallel) 1201
Can’t Use “Acquire” from Software to
Start Scanning 1202
Distorted Graphic Appearance During
Scan 1202
Graphic Looks Clear on Screen, but
Prints Poorly 1202
OCR Text Is Garbled 1203
23 Portable PCs
1205
Evolution of the Portable Computer
Portable System Designs
1183
1184
xiii
Contents
1206
1206
Form Factors 1208
Laptops 1208
Notebooks 1208
Subnotebooks 1209
Palmtop (Handheld
Mini-Notebooks) 1209
Upgrading and Repairing Portables
1210
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Portable System Hardware 1212
Displays 1212
Processors 1217
Mobile Processor Packaging 1225
Chipsets 1232
Memory 1233
Hard Disk Drives 1234
Removable Media 1235
PC Cards (PCMCIA) 1236
Keyboards 1241
Pointing Devices 1242
Batteries 1243
Peripherals 1246
External Displays 1246
Docking Stations 1248
Connectivity 1249
The Traveler’s Survival Kit
Troubleshooting New Installations
1250
Disassembly/Upgrading Preparation
1253
PC Diagnostics
Motherboard 1255
Processor 1256
Chipsets 1257
BIOS 1259
Memory 1260
I/O Ports 1261
Floppy Disk and Removable Drives
Hard Disk Drive
1262
1264
Keyboard and Pointing Device
(Mouse) 1265
Video Card and Display
Sound Card and Speakers
USB Peripherals
1266
1267
1267
Hardware and Software Resources
System Assembly and Disassembly
Assembly Preparation 1270
ESD Protection 1271
Recording Physical
Configuration 1272
1308
Preventive Maintenance 1315
Active Preventive Maintenance
Procedures 1315
Passive Preventive Maintenance
Procedures 1328
1266
Accessories 1267
Heat Sinks/Cooling Fans
Cables 1268
Hardware 1268
1288
Diagnostics Software 1288
The Power On Self Test (POST) 1289
Hardware Diagnostics 1291
General-Purpose Diagnostics
Programs 1293
Operating System Diagnostics 1298
PC Maintenance Tools 1301
Hand Tools 1302
A Word About Hardware 1307
Soldering and Desoldering Tools
Test Equipment 1310
1263
CD/DVD-ROM Drive
CD-R 1264
1285
25 PC Diagnostics, Testing, and
Maintenance 1287
1252
Case and Power Supply
1282
Installing the Operating System 1283
Partitioning the Drive 1283
Format the Drive 1284
Loading the CD-ROM Driver 1284
24 Building or Upgrading
Systems 1251
System Components
Motherboard Installation 1273
Prepare the New Motherboard 1273
Install Memory Modules 1275
Mount the New Motherboard in the
Case 1276
Connect the Power Supply 1278
Connect I/O and Other Cables to the
Motherboard 1279
Install Bus Expansion Cards 1280
Replace the Cover and Connect
External Cables 1281
Run the Motherboard BIOS Setup
Program (CMOS Setup) 1281
1269
1269
Basic Troubleshooting Guidelines 1334
Problems During the POST 1335
Hardware Problems After
Booting 1336
Problems Running Software 1336
Problems with Adapter Cards 1336
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26 Operating System Software
and Troubleshooting 1337
Operating Systems from DOS
to Windows 2000 1338
Operating System Basics
The System BIOS 1340
1338
DOS and DOS Components 1341
IO.SYS (or IBMBIO.COM) 1342
MSDOS.SYS (or IBMDOS.COM) 1343
The Shell or Command Processor
(COMMAND.COM) 1343
DOS Command File Search
Procedure 1344
DOS Versions 1346
Potential DOS Upgrade
Problems 1350
The Boot Process 1351
How DOS Loads and Starts 1352
File Management 1358
Interfacing to Disk Drives 1359
Windows 3.1 1363
16-bit Windows Versions 1364
Loading Windows 3.1 1365
Core Windows Files 1366
32-bit Disk Access 1366
Windows 9x 1368
Windows 9x and DOS
Compared 1368
Windows 9x Versions 1369
Windows 9x Architecture 1369
FAT32 1370
The Windows 9x Boot Process 1371
Windows NT and Windows 2000 1375
Versions 1376
Windows NT and Windows 2000
Startup 1376
Windows NT and Windows 2000
Components 1376
Linux
1377
27 File Systems and Data
Recovery 1379
FAT Disk Structures 1380
Master Partition Boot Record 1381
Primary and Extended FAT
Partitions 1383
Volume Boot Records 1386
Root Directory 1388
File Allocation Tables (FATs) 1391
xv
Contents
Clusters (Allocation Units)
The Data Area 1396
Diagnostic Read-and-Write
Cylinder 1396
VFAT and Long Filenames
1394
1396
FAT32 1399
FAT32 Cluster Sizes 1400
FAT Mirroring 1402
Creating FAT32 Partitions 1403
Converting FAT16 to FAT32 1403
FAT File System Errors 1405
Lost Clusters 1405
Cross-Linked Files 1407
Invalid Files or Directories
FAT Errors 1408
1408
FAT File System Utilities 1409
The CHKDSK Command 1409
CHKDSK Operation 1411
The RECOVER Command 1412
SCANDISK 1412
Disk Defragmentation 1414
Third-Party Programs 1416
NTFS 1417
NTFS Architecture 1418
NTFS Compatibility 1419
Creating NTFS Drives 1419
NTFS Tools 1420
Common Drive Error Messages and
Solutions 1420
Missing Operating System 1420
NO ROM BASIC - SYSTEM
HALTED 1421
Boot Error Press F1 to Retry 1421
Invalid Drive Specification 1421
Invalid Media Type 1421
Hard Disk Controller Failure 1422
General File System Troubleshooting
28 A Final Word
1422
1423
Manuals (Documentation) 1425
Basic System Documentation 1427
Component and Peripheral
Documentation 1428
Chip and Chipset
Documentation 1430
Manufacturer System-Specific
Documentation 1433
Magazines
1433
Online Resources
1434
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Seminars
1435
Machines
1435
CompTIA A+ Core Examination
Objective Map 1436
1.0 Installation, Configuration, and
Upgrading 1437
2.0 Diagnosing and
Troubleshooting 1439
3.0 Safety and Preventive
Maintenance 1440
4.0 Motherboard/Processors/
Memory 1441
5.0 Printers 1442
6.0 Portable Systems 1443
7.0 Basic Networking 1443
8.0 Customer Satisfaction 1444
In Conclusion
1444
A Web Site List
B Glossary
1447
1451
C Making the Most Of
PartitionMagic and
DriveImage 1529
Putting PartitionMagic to Work 1530
The Benefits of Several
Partitions 1530
Changing Partition File Formats 1531
Making More Room on a
Partition 1531
Increase Drive Performance 1532
Putting DriveImage to Work 1532
Upgrading to a New Hard Drive with
DriveImage 1533
Upgrading to a New Drive from a
DriveImage Image File 1533
Creating Backup Image Files 1534
Restoring Image File Backups 1534
Making Bootable Backup Image
File CDs 1535
Exploring the Professional Uses of
DriveImage 1535
Index
1537
Vendor Database
on CD
Hard Drive Specifications
on CD
Technical Reference
on CD
IBM Personal Computer
Family Hardware on CD
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To Lynn:
Another year, another edition… Now ist der time ven ve dahnce!
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About the Author
Scott Mueller is president of Mueller Technical Research, an international research and corporate training firm. Since 1982, MTR has specialized in the industry’s longest running, most indepth, accurate and effective corporate PC hardware and technical training seminars,
maintaining a client list that includes Fortune 500 companies, the U.S. and foreign governments, major software and hardware corporations, as well as PC enthusiasts and entrepreneurs.
His seminars have been presented to thousands of PC support professionals throughout the
world.
Scott Mueller has developed and presented training courses in all areas of PC hardware and
software. He is an expert in PC hardware, operating systems, and data-recovery techniques. For
more information about a custom PC hardware or data recovery training seminar for your organization, contact Lynn at
Mueller Technical Research
21 Spring Lane
Barrington Hills, IL 60010-9009
(847) 854-6794
(847) 854-6795 Fax
Internet: scottmueller@compuserve.com
Web: http://www.m-tr.com
Scott has many popular books, articles, and course materials to his credit, including Upgrading
and Repairing PCs, which has sold more than 2 million copies, making it by far the most popular PC hardware book on the market today. His two hour video titled Your PC—The Inside Story
is available through LearnKey, Inc. For ordering information, contact
LearnKey, Inc.
1845 West Sunset Boulevard
St. George, UT 84770
(800) 865-0165
(801) 674-9733
(801) 674-9734 Fax
If you have questions about PC hardware, suggestions for the next edition of the book, or any
comments in general, send them to Scott via email at scottmueller@compuserve.com.
When he is not working on PC-related books or teaching seminars, Scott can usually be found
in the garage working on vehicle performance projects. This year a Harley Road King is taking
most of his time, and he promises to finish the Impala next.
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Special Thanks to…
Mark Edward Soper is a writer, editor, and trainer who has worked with IBM-compatible PCs
since 1984. Mark spent plenty of time in the trenches as a technical support specialist and technical salesman before his first computer-related articles were published in 1988. He has written
over 100 articles on a wide variety of topics from scanner upgrades to Web-enabled presentations for major industry publications including WordPerfect Magazine, PCNovice Guides, PCToday,
and SmartComputing. Since 1992 he has taught thousands of students across the country how to
troubleshoot and upgrade their computers, create Web sites, and build basic networks. Mark is a
rail fan from way back, and has also had his photos published in Passenger Train Journal magazine. You can learn more about Mark at his company’s Web site, www.selectsystems.com, and
you can write to him at mesoper@selectsystems.com.
Jeff Sloan is the Dimension OEM BIOS development manager for Dell Computers. Prior to
Dell, he worked at IBM PC Company for 15 years, the last eight of which were spent in PS/2
BIOS development and the Problem Determination SWAT team. He has a BS in computer
science from University of Pittsburgh, 1979, and is currently working on an MS in Software
Engineering at Southwest Texas State. Jeff has tech edited numerous Que books.
Joe Curley is an engineering manager at Dell Computer Corporation, working in audio,
motion video, and graphics development. Prior to Dell, Joe worked for Tseng Labs, Inc. and was
a pioneer in Super VGA graphics development in numerous roles, including general manager
for Advanced Systems development. Joe has spoken at several leading industry conferences,
including the Windows Hardware Engineering Conference, about topics ranging from I/O bus
and PC architecture to graphics memory architecture.
Anthony Armstrong is a development engineer working for Dell Computer Corporation on
PC motherboards for the Dimension and Optiplex lines of business. Anthony has previously
worked for IBM in the PowerPC reference platform test group and currently has one personal
computer-related patent pending. Anthony is a computer engineering graduate of the
University of Texas at Austin.
Doug Klippert is an independent contract trainer living in Tacoma, Washington. He is a
Microsoft Certified Software Engineer (MCSE) and a Microsoft Certified Trainer (MCT). He is
also a Microsoft Office User Specialist, Master in Office 97. Doug has a BA in accounting and an
MBA in public administration. He can be reached at doug@klippert.com. Doug has tech edited
numerous Que books.
Pete Lenges is a technical software instructor for New Horizons Computer Learning Centers,
one of the world’s largest training integrators. He is an A+ certified technician with a specialty
in Microsoft operating systems as well as an MCT (Microsoft Certified Trainer) and MCP
(Microsoft Certified Professional). He currently conducts both hardware and software classes at
the Indianapolis facility and also assists in the everyday management of his company’s
LAN/WAN.
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Karen Weinstein is an independent computer consultant living in North Potomac, Maryland.
She has had over a decade of experience in PC sales and support. Karen has a BS in business
administration from the University of Maryland.
Kent Easley is an assistant professor of computer information systems at Howard College in
Big Spring, Texas. He teaches introductory computer science, networking, and programming. He
is a Microsoft Certified Professional and supervises the Microsoft Authorized Academic Training
Program (AATP) at Howard College. He has experience as a network administrator and as a systems librarian. Kent has tech edited numerous Que books. He can be reached by email at
keasley@hc.cc.tx.us.
Ariel Silverstone has been involved in the computer industry for over 15 years. He has consulted nationally for Fortune 1000 firms on the implementation of management information
systems and networking systems. He has designed and set up hundreds of networks over the
years, including using all versions of NetWare and Windows NT Server. For five years, he has
been the chief technical officer for a computer systems integrator in Indiana. While no longer a
professional programmer, he is competent in a variety of computer languages, including both
low- and high-level languages. He has been a technical reviewer over 20 books, including titles
on Windows NT, NetWare, networking, Windows 2000, Cisco routers, and firewalls.
Acknowledgments
This Eleventh Edition is the product of a great deal of additional research and development
over the previous editions. Several people have helped me with both the research and production of this book. I would like to thank the following people:
First, a very special thanks to my wife and partner, Lynn. This book continues to be an incredible burden on both our business and family life, and she has to put up with a lot! Apparently I
can be slightly incorrigible after staying up all night writing, drinking Jolt, and eating chocolate
covered raisins. <g> Lynn is also excellent at dealing with the many companies we have to contact for product information and research. She is the backbone of MTR.
Thanks to Lisa Carlson of Mueller Technical Research for helping with product research and
office management. She has fantastic organizational skills that have been a tremendous help in
managing all of the information that comes into and goes out of this office.
I must give a special thanks to Jill Byus, Rick Kughen, and Jim Minatel at Que. They are my editorial and publishing team, and have all worked so incredibly hard to make this the best book
possible. They have consistently pressed me to improve the content of this book. You guys are
the best!
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Page xxi
I would also like to say thanks to Mark Soper, who added expertise in areas that I might tend to
neglect. Also thanks to all the technical editors who checked my work and questioned me at
every turn, as well as the numerous other editors, illustrators, and staff at Que who work so
hard to get this book out!
Thanks to all the companies who have provided hardware, software, and research information
that has been helpful in developing this book. Thanks to David Means for feedback from the
trenches about various products and especially data recovery information.
Thanks to all the readers who have emailed me with suggestions concerning this book; I welcome all your comments. A special thanks to Paul Reid who always has many suggestions to
offer for improving the book and making it more technically accurate.
Finally, I would like to thank the more than 10,000 people who have attended my seminars;
you may not realize how much I learn from each of you and all your questions! Thanks also to
those of you on the Internet and CompuServe forums with both questions and answers, from
which I have also learned a great deal.
Tell Us What You Think!
As the reader of this book, you are our most important critic and commentator. We value your
opinion and want to know what we’re doing right, what we could do better, what areas you’d
like to see us publish in, and any other words of wisdom you’re willing to pass our way.
As the associate publisher for this book, I welcome your comments. You can fax, email, or write
me directly to let me know what you did or didn’t like about this book—as well as what we can
do to make our books stronger.
While I cannot help you with technical problems related to the topics covered in this book, Scott
Mueller welcomes your technical questions. The best way to reach him is by email at
scottmueller@compuserve.com.
When you write, please be sure to include this book’s title and author as well as your name and
phone or fax number. I will carefully review your comments and share them with the author
and editors who worked on the book.
Fax:
317.817.7070
Email:
hardware@mcp.com
Mail:
Macmillan Computer Publishing
201 West 103rd Street
Indianapolis, IN 46290 USA
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Introduction
Welcome to Upgrading and Repairing PCs, Eleventh Edition. More than just a minor revision, this
new edition contains hundreds of pages of new material and extensive updates. The PC industry is moving faster than ever, and this book is the most accurate, complete, and up-to-date
book of its type on the market today.
This book is for people who want to upgrade, repair, maintain, and troubleshoot computers or
for those enthusiasts who want to know more about PC hardware. This book covers the full
range of PC-compatible systems from the oldest 8-bit machines to the latest in high-end 64-bit
PC-based workstations. If you need to know about everything from the original PC to the latest
in PC technology on the market today, this book is definitely for you.
This book covers state-of-the-art hardware and accessories that make the most modern personal
computers easier, faster, and more productive to use. Hardware coverage includes all the Intel
and Intel-compatible processors through the latest Pentium III, Celeron, and AMD CPU chips;
new cache and main memory technology; PCI and AGP local bus technology; CD-ROM drives;
tape backups; sound boards; PC-card and Cardbus devices for laptops; IDE and SCSI interface
devices; larger and faster hard drives; and new video adapter and display capabilities.
The comprehensive coverage of the PC-compatible personal computer in this book has consistently won acclaim since debuting as the first book of its kind on the market in 1988. Now
with the release of this 11th Edition, Upgrading and Repairing PCs continues its role as not only
the best-selling book of its type, but also the most comprehensive and complete reference on
even the most modern systems—those based on cutting-edge hardware and software. This book
examines PCs in depth, outlines the differences among them, and presents options for configuring each system.
Sections of this book provide detailed information about each internal component of a personal computer system, from the processor to the keyboard and video display. This book examines the options available in modern, high-performance PC configurations and how to use
them to your advantage; it focuses on much of the hardware and software available today and
specifies the optimum configurations for achieving maximum benefit for the time and money
you spend. At a glance, here are the major system components, peripherals, technologies, and
processes covered in this edition of Upgrading and Repairing PCs:
■ Pentium III, Pentium II, Celeron, Xeon, and earlier central processing unit (CPU) chips as
well as Intel-compatible processors from AMD, Cyrix, and other vendors. The processor is
one of the most important parts of a PC, and this book features more extensive and
updated processor coverage than ever before.
■ The latest processor-upgrade socket and slot specifications, including expanded coverage
of Super7 motherboards and Intel’s new Socket 370.
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■ New motherboard designs, including the ATX, WTX, micro-ATX, and NLX form factors.
This new edition features the most accurate, detailed and complete reference to PC
motherboards that you will find.
■ The latest chipsets for current processor families, including all new coverage of the Intel
810 chipset, as well as new members of the 440 chipset family, including the 440ZX,
440GX, and 440NX.
■ Special bus architectures and devices, including high-speed PCI (Peripheral Component
Interconnect), AGP (Accelerated Graphics Port), and the 100MHz processor bus.
■ Bus and system resources that often conflict such as interrupt request (IRQ) lines, Direct
Memory Access (DMA) channels, and input/output (I/O) port addresses.
■ Plug-and-Play (PnP) architecture for setting system resources automatically, including features such as IRQ steering, which allows you to share the IRQ lines—the resource most
in-contention in a modern PC.
■ All new coverage of the BIOS, including detailed coverage of BIOS setup utilities, Flash
upgradable BIOSes, and Plug-and-Play BIOS. The CD accompanying this book also contains BIOS error codes, beep codes, and error messages for Phoenix, AMI, Award, Microid
Research, and IBM BIOSes.
■ Greatly expanded coverage of IDE and SCSI includes in-depth looks at hard drive interfaces and technologies, including new IDE specifications such as Ultra ATA/33, UltraATA/66, and the latest on SCSI-3.
■ Floppy drives and other removable storage devices such as Zip and LS-120 (SuperDisk)
drives, tape drives, and recordable CDs.
■ New coverage of drive installation and configuration, including steps for partitioning
hard drives, mapping drive letters, and transferring data from an old drive to a new
drive.
■ Expanded coverage of burgeoning CD technologies, including the newest MultiBeam CDROMs. CD-R/CD-RW coverage now includes detailed steps and advice for avoiding buffer
under-runs, creating bootable CDs, and selecting the most reliable media.
■ Increasing system memory capacity with SIMM, DIMM, and RIMM modules and increasing system reliability with ECC RAM.
■ New types of memory, including Synchronous Pipeline Burst cache, EDO RAM, Burst
EDO, Synchronous DRAM, and Rambus DRAM.
■ Large-screen Super VGA monitors, flat-panel LED displays, high-speed graphics adapters,
and 3D graphics accelerators. Includes advice for choosing a 3D accelerator to optimize
your system for game play, as well as coverage of 3D technologies, chipsets and APIs.
■ Peripheral devices such as sound cards, modems, DVD drives, and network interface
cards.
■ PC-card and Cardbus devices for laptops.
■ Laser and dot-matrix printer features, maintenance, and repair. Also includes all new coverage of scanners and scanning technology.
The Eleventh Edition includes more detailed troubleshooting advice that will help you track
down problems with your memory, system resources, new drive installations, BIOS, I/O
addresses, video and audio performance, modems, and much more.
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This is the Chapter Title
This book also focuses on software problems, starting with the basics of how an operating system such as DOS or Windows works with your system hardware to start your system. You also
learn how to troubleshoot and avoid problems involving system hardware, the operating system, and applications software.
This book is the result of years of research and development in the production of my PC hardware, operating system, and data recovery seminars. Since 1982, I have personally taught (and
still teach) thousands of people about PC troubleshooting, upgrading, maintenance, repair, and
data recovery. This book represents the culmination of many years of field experience and
knowledge culled from the experiences of thousands of others. What originally started out as a
simple course workbook has over the years grown into a complete reference on the subject.
Now you can benefit from this experience and research.
What Are the Main Objectives of This
Book?
Upgrading and Repairing PCs focuses on several objectives. The primary objective is to help you
learn how to maintain, upgrade, and repair your PC system. To that end, Upgrading and
Repairing PCs helps you fully understand the family of computers that has grown from the original IBM PC, including all PC-compatible systems. This book discusses all areas of system
improvement such as floppy disks, hard disks, central processing units, and power-supply
improvements. The book discusses proper system and component care; it specifies the most
failure-prone items in different PC systems and tells you how to locate and identify a failing
component. You’ll learn about powerful diagnostics hardware and software that enable a system to help you determine the cause of a problem and how to repair it.
PCs are moving forward rapidly in power and capabilities. Processor performance increases
with every new chip design. Upgrading and Repairing PCs helps you gain an understanding of all
the processors used in PC-compatible computer systems.
This book covers the important differences between major system architectures from the original Industry Standard Architecture (ISA) to the latest in PCI and AGP systems. Upgrading and
Repairing PCs covers each of these system architectures and their adapter boards to help you
make decisions about which kind of system you want to buy in the future, and to help you
upgrade and troubleshoot such systems.
The amount of storage space available to modern PCs is increasing geometrically. Upgrading and
Repairing PCs covers storage options ranging from larger, faster hard drives to state-of-the-art
storage devices. In addition, it provides detailed information on upgrading and troubleshooting
system RAM.
When you finish reading this book, you should have the knowledge to upgrade, troubleshoot,
and repair almost all systems and components.
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Who Should Use This Book?
Upgrading and Repairing PCs is designed for people who want a thorough understanding of how
their PC systems work. Each section fully explains common and not-so-common problems,
what causes problems, and how to handle problems when they arise. You will gain an understanding of disk configuration and interfacing, for example, that can improve your diagnostics
and troubleshooting skills. You’ll develop a feel for what goes on in a system so that you can
rely on your own judgment and observations and not some table of canned troubleshooting
steps.
Upgrading and Repairing PCs is written for people who will select, install, configure, maintain,
and repair systems they or their companies use. To accomplish these tasks, you need a level of
knowledge much higher than that of an average system user. You must know exactly which
tool to use for a task and how to use the tool correctly. This book can help you achieve this
level of knowledge.
What Is in This Book?
This book is organized into chapters that cover the components of a PC system. There are a
few chapters that serve to introduce or expand in an area not specifically component-related,
but most parts in the PC will have a dedicated chapter or section, which will aid you in finding
the information you want. Also note that the index has been improved greatly over previous
editions, which will further aid in finding information in a book of this size.
Chapters 1 and 2 of this book serve primarily as an introduction. Chapter 1, “Personal
Computer Background,” begins with an introduction to the development of the original IBM
PC and PC-compatibles. This chapter incorporates some of the historical events that led to the
development of the microprocessor and the PC. Chapter 2, “PC Components, Features, and
System Design,” provides information about the different types of systems you encounter and
what separates one type of system from another, including the types of system buses that differentiate systems. Chapter 2 also provides an overview of the types of PC systems that help
build a foundation of knowledge essential for the remainder of the book, and it offers some
insight as to how the PC market is driven and where components and technologies are
sourced.
Chapters 3–6 cover the primary system components of a PC. Chapter 3, “Microprocessors,”
goes into detail about the central processing unit, or main processor, including those from
Intel, AMD, and other companies. Chapter 4, “Motherboards and Buses,” covers the motherboard, chipsets, motherboard components, and system buses in detail. Because the processor
and motherboard are perhaps the most significant parts of the PC, Chapters 3 and 4 were a primary focus of mine when rewriting this book. They have received extensive updates and a
great deal of new material has been added.
Chapter 5, “BIOS,” has a detailed discussion of the system BIOS including types, features,
and upgrades. This has grown from a section of the book to a complete chapter, with more
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information on this subject than ever before. Be sure to see the exhaustive list of BIOS codes
and error messages I’ve included on the CD-ROM. They’re all printable, so be sure to print the
codes for your BIOS in case you need them later.
Chapter 6, “Memory,” gives a detailed discussion of PC memory, including the latest in cache
and main memory specifications. Next to the processor and motherboard, the system memory
is one of the most important parts of a PC. Memory is also one of the most difficult things to
understand, as it is somewhat intangible and not always obvious how it works. This chapter
has received extensive updates in order to make memory technology more understandable, as
well as to cover the newest technologies on the market today. Coverage of cache memory has
been updated in order to help you understand this difficult subject and know exactly how the
different levels of cache in a modern PC function, interact, and affect system performance.
Chapter 7, “The IDE Interface,” gives a detailed discussion of ATA/IDE, including types and
specifications. This includes coverage of the new Ultra-ATA modes that allow 33MB/sec and
66MB/sec operation. Chapter 8, “The SCSI Interface,” includes a discussion of SCSI including
the new higher speed modes possible with SCSI-3. The SCSI chapter covers the new Low
Voltage Differential signaling used by some of the higher speed devices on the market, as well
as the latest information on cables, terminators, and SCSI configurations.
Chapter 9, “Magnetic Storage Principles,” details the inner workings of magnetic storage
devices such as disk and tape drives. Chapter 10, “Hard Disk Storage,” details the function and
operation of hard disk drives, while Chapter 11, “Floppy Disk Storage,” does the same thing for
floppy drives. Chapter 12, “High-Capacity Removable Disk Storage,” covers removable storage
drives such as SuperDisk (LS-120), Zip, and tape drives. Chapter 13, “Optical Storage,” covers
optical drives and storage using CD and DVD technology, including CD recorders, rewritable
CDs, and other optical technologies. This chapter features extensive updates on DVD as well as
all the CD recording technology. Chapter 14, “Physical Drive Installation and Configuration,”
covers how to install drives of all kinds in a PC system.
Chapter 15, “Video Hardware,” covers everything there is to know about video cards and displays. Chapter 16, “Serial, Parallel, and Other I/O Interfaces,” covers the standard serial and
parallel ports still found in most systems, as well as newer technology such as USB and iLink
(FireWire). Chapter 17, “Input Devices,” covers keyboards, pointing devices, and game ports
used to communicate with a PC. Chapter 18, “Internet Connectivity,” covers all the different
methods for connecting to the Net. Chapter 19, “Local Area Networking,” covers PC-based
local area networks in detail. Chapter 20, “Audio Hardware,” covers sound and sound-related
devices, including sound boards and speaker systems. Chapter 21, “Power Supply and
Chassis/Case,” is a detailed investigation of the power supply, which still remains the primary
cause for PC system problems and failures. Chapter 22, “Printers and Scanners,” covers the various types of printers and scanners in detail.
Chapter 23, “Portable PCs,” covers portable systems including laptop and notebook systems. It
also focuses on all the technology unique and peculiar to portable systems, such as mobile
processors, display, battery, and other technologies.
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Chapter 24, “Building or Upgrading Systems,” focuses on buying or building a PC-compatible
system as well as system upgrades and improvements. This information is useful, especially if
you make purchasing decisions, and also serves as a general guideline for features that make a
certain compatible computer a good or bad choice. The more adventurous can use this information to assemble their own custom system from scratch. Physical disassembly and assembly
procedures are also discussed.
Chapter 25, “PC Diagnostics, Testing, and Maintenance,” covers diagnostic and testing tools
and procedures. This chapter also adds more information on general PC troubleshooting and
problem determination. Chapter 26, “Operating Systems Software and Troubleshooting,” covers
operating system software and troubleshooting. Chapter 27, “File Systems and Data Recovery,”
covers file systems and data recovery procedures.
Chapter 28, “A Final Word,” offers closure by tying all the technologies together and providing
suggestions on additional places to find information.
What’s New and Special About the Eleventh
Edition
Many of you who are reading this have purchased one or more of the previous editions. Based
on your letters, emails, and other correspondence, I know that as much as you value each new
edition, you want to know what new information I’m bringing you. So here is a short list of
the major improvements to this edition:
■ As the PC industry continues to move further away from “IBM compatible” thinking and
nomenclature, this edition is doing the same. In Chapter 2 I discuss who controls the PC
hardware industry and what effect this control has on you.
■ The updating of Chapter 3 involved a major reorganization of the chapter and many
pages of new coverage. The new organization looks at all the relevant processors (and
coprocessors and processor upgrades) in terms of the family of processor they belong to.
The coverage of Pentium II, III, and Celeron processors has been strengthened with upto-date listings of steppings, processors from AMD, Cyrix, and other vendors have been
given more coverage. Cutting-edge features such as on-die L2 cache are explained in
more detail as well. The latest processor slots and sockets are covered, including Slot 1,
Slot 2, Socket 370, and the Super7 socket architecture. I hope you will like the substantial
additions of illustrations and photographs that better show items such as socket types,
processor features, and markings.
■ Chapter 4 takes the new approach of covering the motherboards and the buses found on
the motherboards together as one topic. In addition, you will find extensive new coverage of the latest chipsets, which form the basis of all modern motherboards. This chapter
includes detailed coverage of the features, capabilities, and limitations of the chipsets in
common use today.
■ Chapter 5 is a new addition to the lineup that delves into how the drivers in a system
work together to act as an interface between the hardware and the operating system software. This chapter also explains ROM chips installed on adapter cards, as well as all the
additional drivers loaded when your system starts up. You’ll also find an in-depth look at
working with the BIOS Setup utility.
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■ Chapter 6 has been reorganized to begin by looking at types of memory and how they
are installed. All of the more recent types of memory, including SDRAM and RDRAM, are
explained in more detail in this edition. You’ll also find answers to often-asked questions
relating memory speed to processor speed and a more thorough explanation of why error
checking is still an important memory feature. This chapter also contains new coverage
of RIMMs, continuity modules, and Rambus memory in general.
■ Chapter 7 and 8 also contain a great deal of new information. Here, you’ll find in-depth
coverage of both interfaces, including ATA/66 and SCSI-3.
■ Chapters 9 and 10 contain expanded coverage of hard drive mechanics and principles of
electromagnetism. Chapter 12 contains the latest information on the SuperDisk drives
and investigates problems with other removable formats such as the Iomega Zip “Click of
Death” syndrome.
■ Chapter 13 contains expanded coverage of CD-R and CD-RW drives, including advice for
writing CDs more reliably and creating bootable CDs. This chapter also includes
improved coverage of DVD and new MultiBeam technology.
■ Chapter 14 walks you through installing drives—hard drives, floppy drives, CD-ROM,
magnetic tape—and helps you set map a letter to the drive.
■ Chapter 15 includes enhanced coverage of video displays—including flat-panel LEDs—
and video cards for gaming and multimedia enthusiasts.
■ Chapter 18 contains a greatly expanded coverage of Internet connectivity options,
including more coverage of 56K connections, ISDN, DSL, DirecPC, and leased lines.
■ Chapter 19 is the perfect primer for those new to networking—at home or in the office.
This chapter provides the background you’ll need to be productive on a network—
whether you’re part of a corporate-wide LAN or simply networking a pair of computers at
home.
■ Chapter 20 helps you optimize your computer’s sound output, whether you are a hardcore gamer, a MIDI musician, or if you want to learn about the MP3 format that is revolutionizing the way musical artists distribute music via the Internet.
■ Chapters 25 and 26 both have new and different coverage. Much of this is a reflection of
newer operating systems such as Windows 98, NT, and Windows 2000. The fact that
troubleshooting and configuration tools are less dependent on hardware system vendors
(such as IBM or Compaq) and more generally are third-party software tools necessitates a
new way to look at setup and testing.
■ Chapter 27 takes an in-depth look at the file system, including new examples that
explain how FAT16, FAT32, and NTFS work. If you’re upgrading to Windows 2000, you’ll
find that choosing the right file system is an important decision to make up-front. This
chapter provides the in-depth background you need to make a sound decision.
Although these are the major changes to the core of the book, every chapter has seen substantial updates. If you thought the additions to the Tenth Anniversary Edition were incredible,
wait until you see what I’ve done with the Eleventh Edition. It is the most comprehensive
overhaul this book has seen since I wrote the first edition 11 years ago!
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The Eleventh Edition CD-ROM
As if everything included in the printed book isn’t enough, this edition contains an all-new
CD-ROM. You’ll find the new content on this CD to be an indispensable addition to this book.
The CD contains
■ Que’s edition of PartitionMagic. Create and manage multiple hard disk partitions with this
powerful application. PartitionMagic allows you to create partitions without first backing
up your data and deleting existing partitions. PartitionMagic also allows you to create
and manage partitions using a native Windows 95/98 and NT executable that operates
from within the Windows interface. The best part is that because you can work within
the Windows interface from the same drive you are partitioning, you don’t have to
spend hours reloading your operating system, applications, and data files.
PartitionMagic allows you to switch between FAT and FAT32 file systems with ease. It
also enables you to manage multiple operating systems in separate partitions.
PartitionMagic includes support for FAT, FAT32, NTFS, HPFS, and Linux ext2 file systems.
You can use PartitionMagic as a replacement to FDISK or use it to tweak your drive partitioning after completing your drive setup with FDISK. If you decide to change partitioning later, run PartitionMagic and reallocate your partitions.
◊◊
See Appendix C, “Making the Most of PartitionMagic and Drive Image” p. 1529.
■ Que’s Edition of Drive Image. Rest easy knowing your data is secure because you’ve created
compressed backups of your hard drives and stored them safely to your Zip, LS-120
SuperDrive, or CD-R. Drive Image creates a carbon copy of your drive, including all optimizations and configurations, allowing you to make a complete backup you can use to
restore your system or make exact duplicates of a system. Drive Image saves all passwords, Registry settings, user profiles, and customizations with the image, saving you
hours of down time.
Create compressed hard-disk image files that are about 40 percent smaller than the used
space on the drive. You can even create and image of your primary partition, store it to a
separate partition, and restore your primary partition in an emergency.
Drive Image supports FAT, FAT32, NTFS, and HPFS file systems, and allows for sector-bysector copying of data from Windows, Linux, UNIX, and NetWare drives.
◊◊
See Appendix C, “Making the Most of PartitionMagic and Drive Image” p. 1529.
Note
PartitionMagic and Drive Image would cost more than $100 if purchased separately. The Que Editions of
both applications are yours for the price of this book. These are fully licensed products, not demos or timeout
versions.
■ A+ Testing Questions from Heathkit. Study for the A+ exams using 150 training questions
from Heathkit Educational Systems, a leader in technical-based education.
The questions appear in an interactive, Windows-based format that allows you to answer
questions as if your were taking the actual tests. Use this book to learn the concepts and
technologies then use the test questions to sharpen your skills and point out areas in
which you need more study.
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Note
If you need additional help studying for A+ Certification, see my Upgrading and Repairing PCs: A+
Certification Study Guide, also published by Que, ISBN 0-7897-2095-7.
■ Hard Drive Specifications from Blue-Planet.com. This database contains hard drive specifications for more than 4,000 hard drives from Seagate, Quantum, Western Digital, Maxtor,
IBM, and many others. This incredibly useful database puts thousands of drive specifications at your fingertips, and the elegant database design allows you to quickly find and
print just the specs you need.
Note
The CD also includes a wealth of legacy PC technical information. See the Technical Reference section on the
CD.
Note
If you are a field technician or someone who frequently works on PCs away from your desk, I recommend picking up a copy of Upgrading and Repairing PCs: Technician’s Portable Reference, also published by Que (ISBN:
0-7897-2096-5). This handy book is filled with many of the tables and technical detail from this book, as well
as boiled down versions of these chapters that put crucial details and technical specifications at your fingertips—
all in a portable book that fits easily in your toolkit or briefcase.
■ Vendor List Database. Use Scott Mueller’s fully searchable database of vendors to locate
addresses, phone numbers, and URLs for all the manufacturers discussed in this book.
This keyword searchable database allows you to search for any vendor or product using
any keyword. Instead of searching through 70+ pages of vendors, search and extract the
data you need.
■ BIOS Codes, Beep Codes, and Error Message. Find complete listings of BIOS codes, beep
codes and error messages from Phoenix, AMI, Award, Microid Research (MR BIOS), and
IBM—as well as some of those used by OEM vendors. If you are service technician, you’ll
find these lists to be an integral part of your troubleshooting arsenal. If you a are a private user, I recommend that you print the codes for your BIOS and keep them in a safe
place in case you need to troubleshoot BIOS errors.
■ Third-Party Software. Use Que’s extensive library of software, including overclocking, Y2K,
and performance benchmarking utilities to tune and optimize your PC.
■ Previous Editions of This Book. If you’re looking for legacy coverage of older technologies,
be sure to check the previous editions of this book that are in PDF format on the CD (the
Fourth, Sixth, and Tenth Anniversary editions are included in their entirety and are fully
printable). Simply use the included Adobe Acrobat Reader software to open and print the
pages you need from the selected editions of this book.
■ IBM Personal Computer Family Hardware Reference. Many of the technologies used in
today’s PCs originated from the original IBM PC, XT, and AT systems. This chapter serves
as a technical reference will prove valuable if you are service technician who is required
to work on all types of computers. If you want to learn how the original PC evolved into
what you use today, this is an excellent place to start.
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A Personal Note
I am so excited about all the new changes in this edition, I can hardly wait for everybody to
see it. The last few months before the release of this new edition were more difficult than
usual, not only in meeting the deadlines that are required to bring it out on schedule, but also
while corresponding with readers and teaching my classes using the previous edition and
knowing I had all the great new information written for this edition. This has been more
noticeable to me this time around because this is perhaps the most extensive update I have
done; there is so much new material added. Well now the wait is over, and this new edition is
now available.
When asked what year was his favorite Corvette, Dave McLellan, former manager of the
Corvette platform at GM, always said “Next year’s model.” Now with the new Eleventh
Edition, next year’s model has just become this year’s model, until next year that is…
During the months leading up to the release of the Eleventh Edition, I and everybody else at
Que have worked hard to make this the best edition ever. I am so grateful to everybody who
has helped me with this book over the last 11 years as well as all the loyal readers who have
been reading this book, many of you since the first edition came out. I have had personal contact with many thousands of you in the seminars I have been teaching since 1982, and all I
can say is I enjoy your comments and even criticisms tremendously. Using this book in a
teaching environment has been a major factor in its development. Some of you might be interested to know that I originally began writing this book in 1985; back then it was used exclusively in my PC hardware seminars before being published by Que in 1988. In one way or
another I have been writing and rewriting this book almost continuously for more than 15
years! In the more than 11 years since it was first published, Upgrading and Repairing PCs has
proven to be not only the first but absolutely the best book of its kind. With the new Eleventh
Edition, it is even better than ever. Your comments, suggestions, and support have helped this
book to become the best PC hardware book on the market. I look forward to hearing your
comments after you see this exciting new edition.
Scott
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1
1
Personal Computer
Background
SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE
Computer History—Before Personal Computers
Modern Computers
The IBM Personal Computer
The PC Industry 18 Years Later
CHAPTER 1
Personal Computer History
1
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Personal Computer Background
Many discoveries and inventions have directly and indirectly contributed to the development of
the personal computer. Examining a few important developmental landmarks can help bring the
entire picture into focus.
Computer History—Before Personal
Computers
The first computers of any kind were simple calculators. Even these evolved from mechanical
devices to electronic digital devices.
Timeline
The following is a timeline of some significant events in computer history. It is not meant to be
complete, just a representation of some of the major landmarks in computer development.
■ 1617. John Napier creates “Napiers Bones,” wooden or ivory rods used for calculating.
■ 1642. Blaise Pascal introduces the Pascaline digital adding machine.
■ 1822. Charles Babbage conceives the Difference Engine, and later the Analytical Engine, a
true general purpose computing machine.
■ 1906. Lee DeForest patents the vacuum tube triode, used as an electronic switch in the first
electronic computers.
■ 1945. John von Neumann wrote “First Draft of a Report on the EDVAC,” in which he outlined the architecture of the modern stored-program computer.
■ 1946. ENIAC was introduced, an electronic computing machine built by John Mauchly and
J. Presper Eckert.
■ 1947. On December 23, William Shockley, Walter Brattain, and John Bardeen successfully
tested the point-contact transistor, setting off the semiconductor revolution.
■ 1949. Maurice Wilkes assembled the EDSAC, the first practical stored-program computer, at
Cambridge University.
■ 1950. Engineering Research Associates of Minneapolis built the ERA 1101, one of the first
commercially produced computers.
■ 1952. The UNIVAC I delivered to the U.S. Census Bureau was the first commercial computer to attract widespread public attention.
■ 1953. IBM shipped its first electronic computer, the 701.
■ 1954. A Silicon-based junction transistor, perfected by Gordon Teal of Texas Instruments
Inc., brought the price of this component down to $2.50.
■ 1954. The IBM 650 magnetic drum calculator established itself as the first mass-produced
computer, with the company selling 450 in one year.
■ 1955. Bell Laboratories announced the first fully transistorized computer, TRADIC.
■ 1956. MIT researchers built the TX-0, the first general-purpose, programmable computer
built with transistors.
■ 1956. The era of magnetic disk storage dawned with IBM’s shipment of a 305 RAMAC to
Zellerbach Paper in San Francisco.
■ 1958. Jack Kilby created the first integrated circuit at Texas Instruments to prove that resistors and capacitors could exist on the same piece of semiconductor material.
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■ 1959. IBM’s 7000 series mainframes were the company’s first transistorized computers.
■ 1959. Robert Noyce’s practical integrated circuit, invented at Fairchild Camera and
Instrument Corp., allowed printing of conducting channels directly on the silicon surface.
■ 1960. Bell Labs designed its Dataphone, the first commercial modem, specifically for converting digital computer data to analog signals for transmission across its long-distance network.
■ 1960. The precursor to the minicomputer, DEC’s PDP-1 sold for $120,000.
■ 1961. According to Datamation magazine, IBM had an 81.2-percent share of the computer
market in 1961, the year in which it introduced the 1400 Series.
■ 1964. CDC’s 6600 supercomputer, designed by Seymour Cray, performed up to three
million instructions per second—a processing speed three times faster than that of its
closest competitor, the IBM Stretch.
■ 1964. IBM announced System/360, a family of six mutually compatible computers and 40
peripherals that could work together.
■ 1964. Online transaction processing made its debut in IBM’s SABRE reservation system, set
up for American Airlines.
■ 1965. Digital Equipment Corp. introduced the PDP-8, the first commercially successful
minicomputer.
■ 1966. Hewlett-Packard entered the general purpose computer business with its HP-2115 for
computation, offering a computational power formerly found only in much larger computers.
■ 1970. Computer-to-computer communication expanded when the Department of Defense
established four nodes on the ARPAnet: the University of California-Santa Barbara and
UCLA, SRI International, and the University of Utah.
■ 1971. A team at IBM’s San Jose Laboratories invented the 8-inch floppy disk.
■ 1971. The first advertisement for a microprocessor, the Intel 4004, appeared in Electronic
News.
■ 1971. The Kenbak-1, one of the first personal computers, advertised for $750 in Scientific
American.
■ 1972. Hewlett-Packard announced the HP-35 as “a fast, extremely accurate electronic slide
rule” with a solid-state memory similar to that of a computer.
■ 1972. Intel’s 8008 microprocessor made its debut.
■ 1972. Steve Wozniak built his “blue box,” a tone generator to make free phone calls.
■ 1973. Robert Metcalfe devised the Ethernet method of network connection at the Xerox
Palo Alto Research Center.
■ 1973. The Micral was the earliest commercial, non-kit personal computer based on a microprocessor, the Intel 8008.
■ 1973. The TV Typewriter, designed by Don Lancaster, provided the first display of alphanumeric information on an ordinary television set.
■ 1974. Researchers at the Xerox Palo Alto Research Center designed the Alto—the first workstation with a built-in mouse for input.
■ 1974. Scelbi advertised its 8H computer, the first commercially advertised U.S. computer
based on a microprocessor, Intel’s 8008.
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Personal Computer Background
■ 1975. Telenet, the first commercial packet-switching network and civilian equivalent of
ARPAnet, was born.
■ 1975. The January edition of Popular Electronics featured the Altair 8800, based on Intel’s
8080 microprocessor, on its cover.
■ 1975. The visual display module (VDM) prototype, designed by Lee Felsenstein, marked the
first implementation of a memory-mapped alphanumeric video display for personal computers.
■ 1976. Steve Wozniak designed the Apple I, a single-board computer.
■ 1976. The 5 1/4-inch flexible disk drive and diskette were introduced by Shugart Associates.
■ 1976. The Cray I made its name as the first commercially successful vector processor.
■ 1977. Tandy Radio Shack introduces the TRS-80.
■ 1977. Apple computer introduces the Apple II.
■ 1977. Commodore introduces the PET (Personal Electronic Transactor).
■ 1978. The VAX 11/780 from Digital Equipment Corp. featured the capability to address up
to 4.3 gigabytes of virtual memory, providing hundreds of times the capacity of most minicomputers.
■ 1979. Motorola introduces the 68000 microprocessor.
■ 1980. John Shoch, at the Xerox Palo Alto Research Center, invented the computer “worm,”
a short program that searched a network for idle processors.
■ 1980. Seagate Technology created the first hard disk drive for microcomputers.
■ 1980. The first optical data storage disk had 60 times the capacity of a 5 1/4-inch floppy
disk.
■ 1981. Adam Osborne completed the first portable computer, the Osborne I, which weighed
24 pounds and cost $1,795.
■ 1981. IBM introduced its PC, igniting a fast growth of the personal computer market.
■ 1981. Sony introduced and shipped the first 3 1/2-inch floppy drives and diskettes.
■ 1983. Apple introduced its Lisa. The first personal computer with a graphical user interface
(GUI).
■ 1983. Compaq Computer Corp. introduced their first PC clone that used the same software
as the IBM PC.
■ 1984. Apple Computer launched the Macintosh, the first successful mouse-driven computer
with a GUI, with a single $1.5 million commercial during the 1984 Super Bowl.
■ 1984. IBM released the PC-AT. Several times faster than original PC and based on the Intel
286 chip. This is the computer all modern PCs are based on.
■ 1985. CD-ROM was introduced from CDs on which music is recorded.
■ 1986. Compaq announced the Deskpro 386, the first computer on the market to use Intel’s
new 386 chip.
■ 1987. IBM introduced its PS/2 machines, which made the 3 1/2-inch floppy disk drive and
VGA video standard for IBM computers.
■ 1988. Apple cofounder Steve Jobs, who left Apple to form his own company, unveiled the
NeXT.
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5
■ 1988. Compaq and other PC-clone makers developed enhanced industry standard architecture, which was better than microchannel and retained compatibility with existing
machines.
■ 1988. Robert Morris’ worm flooded the ARPAnet. Then 23-year-old Morris, the son of a
computer security expert for the National Security Agency, sent a nondestructive worm
through the Internet, causing problems for about 6,000 of the 60,000 hosts linked to the
network.
■ 1989. Intel released the 486 microprocessor, which contained more than 1 million transistors.
■ 1990. The World Wide Web (WWW) was born when Tim Berners-Lee, a researcher at CERN,
the high-energy physics laboratory in Geneva, developed Hypertext Markup Language
(HTML).
Mechanical Calculators
One of the earliest calculating devices on record is the Abacus, which has been known and
widely used for more than 2,000 years. The Abacus is a simple wooden rack holding parallel rods
on which beads are strung. When these beads are manipulated back and forth according to certain rules, several different types of arithmetic operations can be performed.
Math with standard Arabic numbers found its way to Europe in the eighth and ninth centuries.
In the early 1600s a man named Charles Napier (the inventor of logarithms) developed a series of
rods (later called Napier’s Bones) that could be used to assist with numeric multiplication.
Blaise Pascal is normally credited with building the first digital calculating machine in 1642. It
could perform the addition of numbers entered on dials and was intended to help his father, who
was a tax collector. Then in 1671, Gottfried Wilhelm von Leibniz invented a calculator that was
finally built in 1694. His calculating machine could not only add, but by successive adding and
shifting, it could also multiply.
In 1820, Charles Xavier Thomas developed the first commercially successful mechanical calculator that could not only add but also subtract, multiply, and divide. After that, a succession of ever
improving mechanical calculators created by various other inventors followed.
The First Mechanical Computer
Charles Babbage, a mathematics professor in Cambridge England, is considered by many as being
the father of computers because of his two great inventions—each a different type of mechanical
computing engine.
The Difference Engine as he called it was conceived in 1812, and solved polynomial equations by
the method of differences. By 1822, he had built a small working model of his Difference Engine
for demonstration purposes. With financial help from the British government, Babbage started
construction of a full-scale model in 1823. It was intended to be steam-powered, and fully automatic, and would even print the resulting tables.
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Babbage continued work on it for 10 years, however, by 1833 he had lost interest because he now
had an idea for an even better machine, something he described as a general-purpose, fully program-controlled, automatic mechanical digital computer. Babbage called his new machine an
Analytical Engine. The plans for the Analytical Engine specified a parallel decimal computer operating on numbers (words) of 50 decimal digits and with a storage capacity (memory) of 1,000
such numbers. Built-in operations were to include everything that a modern general-purpose
computer would need, even the all-important conditional function, which would allow instructions to be executed in an order depending on certain conditions, not just in numerical
sequence. In modern computers this conditional capability is manifested in the IF statement
found in modern computer languages. The Analytical Engine was also intended to use punched
cards, which would control or program the machine. The machine was to operate automatically,
by steam power, and would require only one attendant.
This Analytical Engine would have been the first true general-purpose computing device. It is
regarded as the first real predecessor to a modern computer because it had all the elements of
what is considered a computer today. These included
■ An input device. Using an idea similar to the looms used in textile mills at the time, a form
of punched cards supplied the input.
■ A control unit. A barrel shaped section with many slats and studs was used to control or program the processor.
■ A processor (or calculator). A computing engine containing hundreds of axles and thousands
of gears about 10 feet tall.
■ Storage. A unit containing more axles and gears that could hold 1,000 50-digit numbers.
■ An output device. Plates designed to fit in a printing press, used to print the final results.
Alas, this potential first computer was never actually completed because of the problems in
machining all the precision gears and mechanisms required. The tooling of the day was simply
not good enough.
An interesting side note is that the punched card idea first proposed by Babbage finally came to
fruition in 1890. That year a competition was held for a better method to tabulate the U.S.
Census information, and Herman Hollerith, a Census Department employee, came up with the
idea for punched cards. Without these cards, they had estimated the census data would take years
to tabulate, with it they were able to finish in about six weeks. Hollerith went on to found the
Tabulating Machine Company, which later became known as IBM.
IBM and other companies at the time developed a series of improved punch-card systems. These
systems were constructed of electromechanical devices such as relays and motors. Such systems
included features to automatically feed in a specified number of cards from a “read-in” station;
perform operations such as addition, multiplication, and sorting; and feed out cards punched
with results. These punched-card computing machines could process from 50–250 cards per
minute, with each card holding up to 80-digit numbers. The punched cards provided a means of
not only input and output, but they also served as a form of memory storage. Punched card
machines did the bulk of the world’s computing for more than 50 years and gave many of the
early computer companies their start.
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Electronic Computers
A physicist named John V. Atanasoff is credited with creating the first true digital electronic computer in 1942, while he worked at Iowa State College. His computer was the first to use modern
digital switching techniques and vacuum tubes as the switches.
Military needs during World War II caused a great thrust forward in the evolution of computers.
Systems were needed to calculate weapons trajectory and other military functions. In 1946, John
P. Eckert, John W. Mauchly, and their associates at the Moore School of Electrical Engineering at
the University of Pennsylvania built the first large scale electronic computer for the military. This
machine became known as ENIAC, the Electrical Numerical Integrator and Calculator. It operated on
10-digit numbers, and could multiply two such numbers at the rate of 300 products per second
by finding the value of each product from a multiplication table stored in its memory. ENIAC
was about 1,000 times faster than the previous generation of electromechanical relay computers.
ENIAC used about 18,000 vacuum tubes, occupied 1,800 square feet (167 square meters) of floor
space, and consumed about 180,000 watts of electrical power. Punched cards served as the input
and output; registers served as adders and also as quick-access read-write storage.
The executable instructions composing a given program were created via specified wiring and
switches that controlled the flow of computations through the machine. As such, ENIAC had to
be rewired and switched for each different program to be run.
Earlier in 1945, the mathematician John Von Neumann demonstrated that a computer could
have a very simple, fixed physical structure and yet be capable of executing any kind of computation effectively by means of proper programmed control without the need for any changes in
hardware. In other words, you could change the program without rewiring the system. Von
Neumann’s ideas, often referred to as the stored-program technique, became fundamental for future
generations of high-speed digital computers and were universally adopted.
The first generation of modern programmed electronic computers to take advantage of these
improvements appeared in 1947. This group of machines included EDVAC and UNIVAC, the first
commercially available computers. These computers included, for the first time, the use of true
random access memory (RAM) for storing parts of the program and data that is needed quickly.
Typically, they were programmed directly in machine language, although by the mid-1950s
progress had been made in several aspects of advanced programming. The standout of the era is
the UNIVAC (UNIVersal Automatic Computer), which was the first true general-purpose computer designed for both alphabetical and numerical uses. This made the UNIVAC a standard for
business, not just science and the military.
Modern Computers
From UNIVAC to the present, computer evolution has moved very rapidly. The first generation
computers were known for using vacuum tubes in their construction. The generation to follow
would use the much smaller and more efficient transistor.
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From Tubes to Transistors
Any modern digital computer is largely a collection of electronic switches. These switches are
used to represent and control the routing of data elements called binary digits (or bits). Because
of the on or off nature of the binary information and signal routing used by the computer, an
efficient electronic switch was required. The first electronic computers used vacuum tubes as
switches, and although the tubes worked, they had many problems.
The type of tube used in early computers was called a triode and was invented by Lee DeForest in
1906. It consists of a cathode and a plate, separated by a control grid, suspended in a glass vacuum tube. The cathode is heated by a red-hot electric filament, which causes it to emit electrons
that are attracted to the plate. The control grid in the middle can control this flow of electrons.
By making it negative, the electrons are repelled back to the cathode; by making it positive, they
are attracted toward the plate. Thus by controlling the grid current, you could control the on/off
output of the plate
Unfortunately, the tube was inefficient as a switch. It consumed a great deal of electrical power
and gave off enormous heat—a significant problem in the earlier systems. Primarily because of
the heat they generated, tubes were notoriously unreliable—one failed every couple of hours or
so in the larger systems.
The invention of the transistor, or semiconductor, was one of the most important developments
leading to the personal computer revolution. The transistor was invented in 1947, and
announced in 1948, by Bell Laboratories engineers John Bardeen, Walter Brattain, and William
Shockley. The transistor, which essentially functions as a solid-state electronic switch, replaced
the much less suitable vacuum tube. Because the transistor was so much smaller and consumed
significantly less power, a computer system built with transistors was also much smaller, faster,
and more efficient than a computer system built with vacuum tubes.
Transistors are made primarily from the elements silicon and germanium, with certain impurities
added. Depending on the impurities added and its electron content, the material becomes known
as either N-Type (negative) or P-Type (positive). Both types are conductors, allowing electricity to
flow in either direction. However, when the two types are joined, a barrier is formed where they
meet that allows current to flow only in one direction when a voltage is present in the right
polarity. This is why they are normally called semiconductors.
A transistor is made from placing two P-N junctions back to back. They are made by sandwiching
a thin wafer of one type of semiconductor material between two wafers of the other type. If the
wafer in-between is made from P-type material, the transistor is designated a NPN. If the wafer inbetween is N-type, the transistor is designated PNP.
In an NPN transistor, the N-type semiconductor material on one side of the wafer is called the
emitter and is normally connected to a negative current. The P-type material in the center is
called the base. And the N-type material on the other side of the base is called the collector.
An NPN transistor compares to a triode tube such that the emitter is equivalent to the cathode,
the base is equivalent to the grid, and the collector is equivalent to the plate. By controlling the
current at the base, you can control the flow of current between the emitter and collector.
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Compared to the tube, the transistor is much more efficient as a switch, and in addition can be
miniaturized to microscopic scale. The latest Pentium II and III microprocessors consist of more
than 27 million transistors on a single chip die!
The conversion from tubes to transistors began the trend toward miniaturization that continues
to this day. Today’s small laptop (or palmtop) PC systems, which run on batteries, have more
computing power than many earlier systems that filled rooms and consumed huge amounts of
electrical power.
Integrated Circuits
The third generation of modern computers is known for using integrated circuits instead of individual transistors. In 1959, engineers at Texas Instruments invented the integrated circuit (IC), a
semiconductor circuit that contains more than one transistor on the same base (or substrate
material) and connects the transistors without wires. The first IC contained only six transistors.
By comparison, the Intel Pentium Pro microprocessor used in many of today’s high-end systems
has more than 5.5 million transistors, and the integral cache built into some of these chips contains as many as an additional 32 million transistors! Today, many ICs have transistor counts in
the multimillion range.
The First Microprocessor
In 1998, Intel celebrated its 30th anniversary. Intel was founded on July 18, 1968, by Robert
Noyce, Gordon Moore, and Andrew Grove. They had a specific goal: to make semiconductor
memory practical and affordable. This was not a given at the time considering that Silicon chipbased memory was at least 100 times more expensive than the magnetic core memory commonly
used in those days. At the time, semiconductor memory was going for about a dollar a bit,
whereas core memory was about a penny a bit. Noyce said, “All we had to do was reduce the cost
by a factor of a hundred, then we’d have the market; and that’s basically what we did.”
By 1970, Intel was known as a successful memory chip company, having introduced a 1Kbit
memory chip much larger than anything else available at the time. (1Kbit equals 1,024 bits, and
a byte equals 8 bits. This chip, therefore, stored only 128 bytes—not much by today’s standards.)
Known as the 1103 dynamic random access memory (DRAM), it became the world’s largest-selling semiconductor device by the end of the following year. By this time Intel had also grown
from the core founders and a handful of others to more than 100 employees.
Because of Intel’s success in memory chip manufacturing and design, Japanese manufacturer
Busicom asked Intel to design a set of chips for a family of high-performance programmable calculators. At the time, all logic chips were custom-designed for each application or product.
Because most chips had to be custom designed specific to a particular application, no one chip
could have any widespread usage.
Busicom’s original design for their calculator called for at least 12 custom chips. Intel engineer
Ted Hoff rejected the unwieldy proposal and instead designed a single-chip, general-purpose logic
device that retrieved its application instructions from semiconductor memory. As the core of a
four-chip set, this central processing unit could be controlled by a program that could essentially
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tailor the function of the chip to the task at hand. The chip was generic in nature, meaning it
could function in designs other than calculators. Previous designs were hard-wired for one purpose, with built-in instructions; this chip would read a variable set of instructions from memory,
which would control the function of the chip. The idea was to design almost an entire computing device on a single chip that could perform different functions, depending on what instructions it was given.
There was one problem with the new chip: Busicom owned the rights to it. Hoff and others knew
that the product had almost limitless application, bringing intelligence to a host of “dumb”
machines. They urged Intel to repurchase the rights to the product. While Intel founders Gordon
Moore and Robert Noyce championed the new chip, others within the company were concerned
that the product would distract Intel from its main focus, making memory. They were finally
convinced by the fact that every four-chip microcomputer set included two memory chips. As the
director of marketing at the time recalled, “Originally, I think we saw it as a way to sell more
memories, and we were willing to make the investment on that basis.”
Intel offered to return Busicom’s $60,000 investment in exchange for the rights to the product.
Struggling with financial troubles, the Japanese company agreed. Nobody else in the industry at
the time, even at Intel, realized the significance of this deal. Of course it paved the way for Intel’s
future in processors. The result was the 1971 introduction of the 4-bit Intel 4004 microcomputer
set (the term microprocessor was not coined until later). Smaller than a thumbnail and packing
2300 transistors, the $200 chip delivered as much computing power as the first electronic computer, ENIAC. By comparison, ENIAC relied on 18,000 vacuum tubes packed into 3,000 cubic feet
(85 cubic meters) when it was built in 1946. The 4004 executed 60,000 operations in one second,
primitive by today’s standards, but a major breakthrough at the time.
Intel introduced the 8008 microcomputer in 1972, which processed eight bits of information at a
time, twice as much as the original chip. By 1981, Intel’s microprocessor family had grown to
include the 16-bit 8086 and the 8-bit 8088 processors. These two chips garnered an unprecedented 2,500 design wins in a single year. Among those designs was a product from IBM that was
to become the first PC.
In 1982, Intel introduced the 286 chip. With 134,000 transistors, it provided about three times
the performance of other 16-bit processors of the time. Featuring on-chip memory management,
the 286 was the first microprocessor that offered software compatibility with its predecessors.
This revolutionary chip was first used in IBM’s benchmark PC-AT.
In 1985 came the Intel386 processor. With a new 32-bit architecture and 275,000 transistors, the
chip could perform more than 5 million instructions every second (MIPS). Compaq’s DESKPRO
386 was the first PC based on the new microprocessor.
Next out of the block was the Intel486 processor in 1989. The new chip had 1.2 million transistors and the first built-in math coprocessor. The 486 was some 50 times faster than the original
4004, equaling the performance of powerful mainframe computers.
In 1993, Intel introduced the first Pentium processor, setting new performance standards with up
to five times the performance of the Intel486 processor. The Pentium processor uses 3.1 million
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transistors to perform up to 90 MIPS—now up to about 1,500 times the speed of the original
4004.
The first processor in the P6 family, called the Pentium Pro processor, was introduced in 1995.
With 5.5 million transistors, it was the first to be packaged with a second die containing highspeed memory cache to accelerate performance. Capable of performing up to 300 MIPS, the
Pentium Pro continues to be a popular choice for multiprocessor servers and high-performance
workstations.
Intel introduced the Pentium II processor in May 1997. Pentium II processors have 7.5 million
transistors packed into a cartridge rather than a conventional chip. The Pentium II family was
augmented in April 1998, with both the low-cost Celeron processor for basic PCs and the highend Pentium II Xeon processor for servers and workstations.
Sometime during the year 2000 we expect to see the new P7 processor, code-named Merced.
This will be Intel’s first processor with 64-bit instructions, and will spawn a whole new category
of operating systems and applications, while still remaining backward-compatible with 32-bit
software.
Personal Computer History
The fourth and current generation of modern computer includes those that incorporate microprocessors in their designs. Of course, part of this fourth generation of computers is the personal
computer, which itself was made possible by the advent of low cost microprocessors and memory.
Birth of the Personal Computer
In 1973, some of the first microcomputer kits based on the 8008 chip were developed. These kits
were little more than demonstration tools and didn’t do much except blink lights. In late 1973,
Intel introduced the 8080 microprocessor, which was 10 times faster than the earlier 8008 chip
and addressed 64K of memory. This was the breakthrough the personal computer industry had
been waiting for.
A company called MITS introduced the Altair kit in a cover story in the January 1975 issue of
Popular Electronics. The Altair kit, considered to be the first personal computer, included an 8080
processor, a power supply, a front panel with a large number of lights, and 256 bytes (not kilobytes) of memory. The kit sold for $395 and had to be assembled. Assembly back then meant you
got out your soldering iron to actually finish the circuit boards, not like today where you can
assemble a system of pre-made components with nothing more than a screwdriver.
The Altair included an open architecture system bus called the S-100 bus because it had 100 pins
per slot. The open architecture meant that anybody could develop boards to fit in these slots and
interface to the system. This prompted various add-ons and peripherals from numerous aftermarket companies. The new processor inspired software companies to write programs, including the
CP/M (Control Program for Microprocessors) operating system and the first version of the
Microsoft BASIC (Beginners All-purpose Symbolic Instruction Code) programming language.
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IBM introduced what can be called its first personal computer in 1975. The Model 5100 had 16K
of memory, a built-in 16-line by 64-character display, a built-in BASIC language interpreter, and a
built-in DC-300 cartridge tape drive for storage. The system’s $9,000 price placed it out of the
mainstream personal computer marketplace, which was dominated by experimenters (affectionately referred to as hackers) who built low-cost kits ($500 or so) as a hobby. Obviously, the IBM
system was not in competition for this low-cost market and did not sell as well by comparison.
The Model 5100 was succeeded by the 5110 and 5120 before IBM introduced what we know as
the IBM Personal Computer (Model 5150). Although the 5100 series preceded the IBM PC, the
older systems and the 5150 IBM PC had nothing in common. The PC IBM turned out was more
closely related to the IBM System/23 DataMaster, an office computer system introduced in 1980.
In fact, many of the engineers who developed the IBM PC had originally worked on the
DataMaster.
In 1976, a new company called Apple Computer introduced the Apple I, which originally sold for
$666. The selling price was an arbitrary number selected by one of the co-founders, Steve Jobs.
This system consisted of a main circuit board screwed to a piece of plywood. A case and power
supply were not included. Only a few of these computers were made, and they reportedly have
sold to collectors for more than $20,000. The Apple II, introduced in 1977, helped set the standard for nearly all the important microcomputers to follow, including the IBM PC.
The microcomputer world was dominated in 1980 by two types of computer systems. One type,
the Apple II, claimed a large following of loyal users and a gigantic software base that was growing at a fantastic rate. The other type, CP/M systems, consisted not of a single system but of all
the many systems that evolved from the original MITS Altair. These systems were compatible
with one another and were distinguished by their use of the CP/M operating system and expansion slots, which followed the S-100 standard. All these systems were built by a variety of companies and sold under various names. For the most part, however, these systems used the same
software and plug-in hardware. It is interesting to note that none of these systems were PC-compatible or Macintosh-compatible, the two primary standards in place today.
A new competitor looming on the horizon was able to see that in order to be successful, a personal computer needed to have an open architecture, slots for expansion, a modular design, and
healthy support from both hardware and software companies other than the original manufacturer of the system. This competitor turned out to be IBM, which was quite surprising at the time
because IBM was not known for systems with these open architecture attributes! IBM in essence
became more like the early Apple, and Apple themselves became like everybody expected IBM to
be. The open architecture of the forthcoming IBM PC and the closed architecture of the forthcoming Macintosh caused a complete turnaround in the industry.
The IBM Personal Computer
At the end of 1980, IBM decided to truly compete in the rapidly growing low-cost personal computer market. The company established what was called the Entry Systems Division, located in
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Boca Raton, Florida, to develop the new system. The division was located intentionally far away
from IBM’s main headquarters in New York, or any other IBM facilities, in order that this new
division be able to operate independently as a separate unit. This small group consisted of 12
engineers and designers under the direction of Don Estridge. The team’s chief designer was Lewis
Eggebrecht. The Entry Systems Division was charged with developing IBM’s first real PC. (IBM
considered the previous 5100 system, developed in 1975, to be an intelligent programmable terminal rather than a genuine computer, even though it truly was a computer.) Nearly all these
engineers had been moved into the new division from the System/23 DataMaster project, which
was a small office computer system introduced in 1980, and was the direct predecessor at IBM to
the IBM PC.
Much of the PC’s design was influenced by the DataMaster design. In the DataMaster’s singlepiece design, the display and keyboard were integrated into the unit. Because these features were
limiting, they became external units on the PC, although the PC keyboard layout and electrical
designs were copied from the DataMaster.
Several other parts of the IBM PC system also were copied from the DataMaster, including the
expansion bus (or input/output slots), which included not only the same physical 62-pin connector, but also almost identical pin specifications. This copying of the bus design was possible
because the PC used the same interrupt controller as the DataMaster and a similar direct memory
access (DMA) controller. Also, expansion cards already designed for the DataMaster could easily
be redesigned to function in the PC.
The DataMaster used an Intel 8085 CPU, which had a 64KB address limit, and an 8-bit internal
and external data bus. This arrangement prompted the PC design team to use the Intel 8088
CPU, which offered a much larger (1MB) memory address limit and an internal 16-bit data bus,
but only an 8-bit external data bus. The 8-bit external data bus and similar instruction set
allowed the 8088 to be easily interfaced into the earlier DataMaster designs.
Estridge and the design team rapidly developed the design and specifications for the new system.
In addition to borrowing from the System/23 DataMaster, the team studied the marketplace,
which also had enormous influence on the IBM PC’s design. The designers looked at the prevailing standards and successful systems available at the time, learned from the success of those systems, and incorporated into the new PC all the features of the popular systems, and more. With
the parameters for design made obvious by the market, IBM produced a system that quite capably
filled its niche in the market.
IBM brought its system from idea to delivery of functioning systems in one year by using existing
designs and purchasing as many components as possible from outside vendors. The Entry
Systems Division was granted autonomy from IBM’s other divisions and could tap resources outside the company, rather than go through the bureaucratic procedures that required exclusive use
of IBM resources. IBM contracted out the PC’s languages and operating system to a small company named Microsoft. That decision was the major factor in establishing Microsoft as the dominant force in PC software today.
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Note
It is interesting to note that IBM had originally contacted Digital Research (the company that created CP/M, then
the most popular personal computer operating system) to have them develop an operating system for the new IBM
PC, but they were leery of working with IBM, and especially balked at the nondisclosure agreement IBM wanted
them to sign. Microsoft jumped on the opportunity left open by Digital Research, and as a result has become one
of the largest software companies in the world. IBM’s use of outside vendors in developing the PC was an open
invitation for the aftermarket to jump in and support the system—and it did.
On Wednesday, August 12, 1981, a new standard was established in the microcomputer industry
with the debut of the IBM PC. Since then, hundreds of millions of PC-compatible systems have
been sold, as the original PC has grown into an enormous family of computers and peripherals.
More software has been written for this computer family than for any other system on the market.
The PC Industry 18 Years Later
In the more than 18 years since the original IBM PC was introduced, many changes have
occurred. The IBM-compatible computer, for example, advanced from a 4.77MHz 8088-based system to 500MHz or faster Pentium II-based systems—nearly 4,000 times faster than the original
IBM PC (in actual processing speed, not just clock speed). The original PC had only one or two
single-sided floppy drives that stored 160KB each using DOS 1.0, whereas modern systems easily
can have 20GB (20 billion bytes) or more of hard disk storage.
A rule of thumb in the computer industry (called Moore’s Law, originally set forth by Intel cofounder Gordon Moore) is that available processor performance and disk-storage capacity doubles
every two years, give or take.
Since the beginning of the PC industry, this pattern has shown no sign of changing.
In addition to performance and storage capacity, another major change since the original IBM PC
was introduced is that IBM is not the only manufacturer of “PC-compatible” systems. IBM originated the PC-compatible standard, of course, but today they no longer set the standards for the
system they originated. More often than not, new standards in the PC industry are developed by
companies and organizations other than IBM. Today, it is Intel and Microsoft who are primarily
responsible for developing and extending the PC hardware and software standards, respectively.
Some have even taken to calling PCs “Wintel” systems, owing to the dominance of those two
companies.
In more recent years Intel and Microsoft have carried the evolution of the PC forward. The introduction of hardware standards such as the PCI (Peripheral Component Interconnect) bus, AGP
(Accelerated Graphics Port) bus, ATX and NLX motherboard form factors, Socket 1 through 8 as
well as Slot 1 and 2 processor interfaces, and numerous others show that Intel is really pushing
PC hardware design these days. In a similar fashion, Microsoft is pushing the software side of
things with the continual evolution of the Windows operating system as well as applications
such as the Office suite.
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Today there are literally hundreds of system manufacturers following the collective PC standard
and producing computers that are fully PC-compatible. There are also thousands of peripheral
manufacturers whose components expand and enhance PC-compatible systems.
PC-compatible systems have thrived, not only because compatible hardware can be assembled
easily, but also because the primary operating system was available not from IBM but from a third
party (Microsoft). The core of the system software is the BIOS (basic input/output system), and
this was also available from third-party companies such as AMI, Award, Phoenix, and others. This
situation allowed other manufacturers to license the operating system and BIOS software and to
sell their own compatible systems. The fact that DOS borrowed the functionality and user interface from both CP/M and UNIX probably had a lot to do with the amount of software that
became available. Later, with the success of Windows, there would be even more reasons for software developers to write programs for PC-compatible systems.
One of the reasons why Apple Macintosh systems will likely never enjoy the success of PC systems is that Apple controls all the primary systems software (BIOS and OS), and has never
licensed it to other companies for use in compatible systems.
At some point in their development, Apple seemed to recognize this flawed stance, and in the
mid-1990s, licensed its software to third-party manufacturers such as Power Computing. After a
short time, Apple cancelled its licensing agreements with other manufacturers. Since Apple
remains essentially a closed system, other companies cannot develop compatible machines,
meaning Macintosh systems are only available from one source—Apple. As such, it seems too late
for them to effectively compete with the PC-compatible juggernaut. It is fortunate for the computing public as a whole that IBM created a more open and extendible standard, which today
finds systems being offered by hundreds of companies in thousands of configurations. This kind
of competition among manufacturers and vendors of PC-compatible systems is the reason why
such systems offer so much performance and so many capabilities for the money.
The IBM-compatible market continues to thrive and prosper. New technology continues to be
integrated into these systems, enabling them to grow with the times. These systems offer a high
value for the money and have plenty of software available to run on them. It’s a safe bet that PCcompatible systems will dominate the personal computer marketplace for the next 15–20 years.
Moore’s Law
In 1965, Gordon Moore was preparing a speech about the growth trends in computer memory, and he made an
interesting observation. When he began to graph the data, he realized there was a striking trend. Each new chip
contained roughly twice as much capacity as its predecessor, and each chip was released within 18–24 months
of the previous chip. If this trend continued, he reasoned, computing power would rise exponentially over relatively
brief periods of time (see Figure 1.1).
Moore’s observation, now known as Moore’s Law, described a trend that has continued to this day and is still
remarkably accurate. It was found to not only describe memory chips, but also accurately describe the growth of
processor power and disk-drive storage capacity. It has become the basis for many industry performance forecasts.
In 26 years, the number of transistors on a chip has increased more than 3,200 times, from 2,300 on the 4004
in 1971 to more than 7.5 million on the Pentium II processor.
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1975
1980
1985
1990
1995
Micro
500
2000 (mlps)
10M
(transistors)
Pentium™
Processor
1M
80486
80386
100K
25
1.0
80286
10K
8086
0.1
8080
4004
Figure 1.1
two years.
0.01
Moore’s Law as applied to processors, showing that transistor count doubles about every
What does the future hold? For PCs, one thing is sure: They will continue to become faster,
smaller, and cheaper. According to Gordon Moore, computing power continues to increase at a
rate of about double the power every two years. This has held true not only for speed but storage
capacity as well. This means that computers you will be purchasing two years from now will be
about twice as fast and store twice as much as what you can purchase today. The really amazing
part is that this rapid pace of evolution shows no signs of letting up.
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17 17
PC Components,
Features, and
System Design
SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE
What Is a PC?
System Types
CHAPTER 2
System Components
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This chapter defines what a PC really is, and then continues by defining the types of PCs on the
market. In addition, the chapter gives an overview of the components found in a modern PC.
What Is a PC?
I normally ask the question, “What exactly is a PC?” when I begin one of my PC hardware seminars. Of course, most people immediately answer that PC stands for personal computer, which in
fact it does. They might then continue by defining a personal computer as any small computer
system purchased and used by an individual. Unfortunately, that definition is not nearly precise
or accurate enough for our purposes. I agree that a PC is a personal computer, but not all personal computers are PCs. For example, an Apple Macintosh system is clearly a personal computer,
but nobody I know would call a Mac a PC, least of all Mac users! For the true definition of what a
PC is, you must look deeper.
Calling something a PC implies that it is something much more specific than just any personal
computer. One thing it implies is a family relation to the first IBM PC from 1981. In fact, I’ll go
so far as to say that IBM literally invented the PC; that is, they designed and created the very first
one, and it was IBM who originally defined and set all the standards that made the PC distinctive
from other personal computers. Note that it is very clear in my mind—as well as in the historical
record—that IBM did not invent the personal computer. (Most recognize the historical origins of
the personal computer in the MITS Altair, introduced in 1975.) IBM did not invent the personal
computer, but they did invent the PC. Some people might take this definition a step further and
define a PC as any personal computer that is “IBM compatible.” In fact, many years back PCs
were called either IBM compatibles or IBM clones, in essence paying homage to the origins of the
PC at IBM.
The reality today is that although IBM clearly designed and created the first PC in 1981 and controlled the development and evolution of the PC standard for several years thereafter, IBM is no
longer in control of the PC standard; that is, they do not dictate what makes up a PC today. IBM
lost control of the PC standard in 1987 when they introduced their PS/2 line of systems. Up until
then, other companies that were producing PCs literally copied IBM’s systems right down to the
chips, connectors, and even the shapes (form factors) of the boards, cases, and power supplies;
after 1987, IBM abandoned many of the standards they created in the first place. That’s why for
many years now I have refrained from using the designation “IBM compatible” when referring
to PCs.
If a PC is no longer an IBM compatible, what is it? The real question seems to be, “Who is in
control of the PC standard today?” That question is best broken down into two parts. First, who
is in control of PC software? Second, who is in control of PC hardware?
Who Controls PC Software?
Most of the people in my seminars don’t even hesitate for a split second when I ask this question; they immediately respond “Microsoft!” I don’t think there is any argument with that
answer. Microsoft clearly controls the operating systems that are used on PCs, which have
migrated from the original MS-DOS to Windows 95/98, Windows NT, and Windows 2000.
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Microsoft has effectively used their control of the PC operating system as leverage to also control
other types of PC software, such as utilities and applications. For example, many utility programs
that were originally offered by independent companies such as disk caching, disk compression,
defragmentation, file structure repair, and even calculators and notepads are now bundled
(included with) in Windows. They have even bundled applications such as Web browsers, insuring an automatic installed base for these applications—much to the dismay of companies that
produce competing versions. Microsoft has also leveraged their control of the operating system to
integrate their own networking software and applications suites more seamlessly into the operating system than others. That’s why they now dominate most of the PC software universe, from
operating systems to utilities, from word processors to spreadsheets.
In the early days of the PC, when IBM was clearly in control of the PC hardware standard, they
hired Microsoft to provide most of the core software for the PC. IBM developed the hardware,
wrote the BIOS (basic input/output system), and then hired Microsoft to develop the Disk
Operating System (DOS) as well as several other programs and utilities for IBM. In what was later
viewed as perhaps the most costly business mistake in history, IBM failed to secure exclusive
rights to the DOS they had contracted from Microsoft, either by purchasing it outright or by an
exclusive license agreement. Instead, IBM licensed it non-exclusively, which subsequently allowed
Microsoft to sell the same MS-DOS code they developed for IBM to any other company that was
interested. Early PC cloners such as Compaq eagerly licensed this same operating system code,
and suddenly you could purchase the same basic MS-DOS operating system with several different
company names on the box. In retrospect, that single contractual error made Microsoft into the
dominant software company it is today, and subsequently caused IBM to lose control of the very
PC standard they had created.
As a writer myself (words, not software) I can appreciate what an incredible oversight this was.
Imagine that a book publisher comes up with a great idea for a very popular book, and then contracts with and subsequently pays an author to write it. Then, by virtue of a poorly written contract, the author discovers that he can legally sell the very same book (perhaps with a different
title) to all the competitors of the original publisher. Of course no publisher I know would allow
this to happen, yet that is exactly what IBM allowed Microsoft to do back in 1981. By virtue of
their deal with Microsoft, IBM had essentially lost control of the software they commissioned for
their new PC from day one.
◊◊ See “BIOS,” p. 345.
It is interesting to note that in the PC business software enjoys copyright protection, whereas
hardware can only be protected by patents, which are difficult and time consuming to get and
which expire after 17 years. To patent something requires that it be a unique and substantially
new design. This made it impossible to patent most aspects of the IBM PC because it was
designed using previously existing parts that anybody could purchase off the shelf! In fact, most
of the important parts for the original PC came from Intel, such as the 8088 processor, 8284 clock
generator, 8253/54 timer, 8259 interrupt controller, 8237 DMA (Direct Memory Access) controller, 8255 peripheral interface, and the 8288 bus controller. These are the chips that made up
the heart and soul of the original PC.
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Because the design of the original PC was not wholly patentable, anybody could duplicate the
hardware of the IBM PC. All they had to do was purchase the same chips from the same manufacturers and suppliers that IBM used and design a new motherboard with a similar circuit.
Seemingly as if to aid in this, IBM even published complete schematic diagrams of their motherboards and all their adapter cards in very detailed and easily available Technical Reference manuals. I have several of these early IBM manuals and still refer to them from time to time for specific
component-level PC design information. In fact, I still recommend these original manuals to anybody who wants to delve deeply into PC design.
The difficult part of copying the IBM PC was the software, which is protected by copyright law.
Phoenix Software was among the first to develop a legal way around this problem, which enabled
them to functionally duplicate (but not exactly copy) software such as the BIOS (basic input/output system). The BIOS is defined as the core set of control software, which drives the hardware
devices in the system directly. These types of programs are normally called device drivers, so in
essence the BIOS is a collection of all the core device drivers used to operate and control the system hardware. What is called the operating system (such as DOS or Windows) uses the drivers in
the BIOS to control and communicate with the various hardware and peripherals in the system.
Phoenix’s method for duplicating the BIOS legally was an ingenious form of reverse-engineering.
They hired two teams of software engineers, the second of which had to be specially screened to
consist only of people who had never seen or studied the IBM BIOS code. The first team did
study the IBM BIOS, and wrote as complete a description of what it did as possible. The second
team read the description written by the first team, and set out to write from scratch a new BIOS
that did everything the first team described. The end result was a new BIOS written from scratch
with code that, although not identical to IBM’s, had exactly the same functionality.
Phoenix called this a “clean room” approach to reverse engineering software, and it can escape
any legal attack. Because IBM’s original PC BIOS consisted of only 8KB of code and had limited
functionality, duplicating it through the clean room approach was not very difficult or time consuming. As the IBM BIOS evolved, Phoenix—as well as the other BIOS companies—found it relatively easy to keep in step with any changes IBM might make. Discounting the POST (power on
self test) or BIOS Setup program (used for configuring the system) portion of the BIOS, most
BIOSes, even today, have only about 32K of active code. Today not only Phoenix, but also others
such as AMI and Microid Research, are producing BIOS software for PC system manufacturers.
After the hardware and the BIOS of the IBM PC were duplicated, all that was needed to produce a
fully IBM-compatible system was DOS. Reverse engineering DOS—even with the clean room
approach—would have been a daunting task because DOS is much larger than the BIOS and consists of many more programs and functions. Also, the operating system has evolved and changed
more often than the BIOS, which by comparison has remained relatively constant. This means
that the only way to get DOS on an IBM compatible is to license it. This is where Microsoft
comes in. Because IBM (who hired Microsoft to write DOS in the first place) did not ensure that
Microsoft signed an exclusive license agreement, Microsoft was free to sell the same DOS to anybody. With a licensed copy of MS-DOS, the last piece was in place and the floodgates were open
for IBM-compatible systems to be produced whether IBM liked it or not.
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In retrospect, this is exactly why there are no clones or compatibles of the Apple Macintosh system. It is not that Mac systems cannot be duplicated; in fact, the Mac hardware is fairly simple
and easy to produce using off-the-shelf parts. The real problem is that Apple owns the MAC OS as
well as the BIOS, and because they have seen fit not to license them, no other company can sell
an Apple-compatible system. Also, note that the Mac BIOS and OS are very tightly integrated; the
Mac BIOS is very large and complex, and it is essentially a part of the OS, unlike the much more
simple and easily duplicated BIOS found on PCs. The greater complexity and integration has
allowed both the Mac BIOS and OS to escape any clean room duplication efforts. This means that
without Apple’s blessing (in the form of licensing), no Mac clones are likely to ever exist.
It might be interesting to note that during ‘96–’97 there was an effort by the more liberated
thinkers at Apple to license their BIOS/OS combination, and several Mac compatible machines
were not only developed, but also were produced and sold. Companies such as Sony, Power
Computing, Radius, and even Motorola had invested millions of dollars in developing these systems, but shortly after these first Mac clones were sold, Apple rudely canceled all licensing! This
was apparently the result of an edict from Steve Jobs, who had been hired back to run the company and who was one of the original architects of the closed-box proprietary design Macintosh
system in the first place. By canceling these licenses, Apple has virtually guaranteed that their
systems will never be a mainstream success. Along with their smaller market share come much
higher system costs, fewer available software applications, and fewer hardware upgrades as compared to PCs. The proprietary design also means that major repair or upgrade components such
as motherboards, power supplies, and cases are available only from Apple at very high prices, and
upgrades of these components are normally not cost effective.
I often think that if Apple had a different view and had licensed their OS and BIOS early-on, this
book might be called “Upgrading and Repairing Macs” instead!
In summary, because IBM did not own DOS (or Windows) but licensed it non-exclusively from
Microsoft, anybody else who wanted to put MS-DOS or Windows on their system could license
the code from Microsoft. This enabled any company who wanted to develop an IBM-compatible
system to circumvent IBM completely, and yet produce a functionally identical machine. Because
people desire backward compatibility, when one company controls the operating system, they
naturally control all the software that goes around it, including everything from drivers to application programs. As long as PCs are used with Microsoft operating systems, they will have the
upper hand in controlling PC software.
Who Controls PC Hardware?
Although it is clear that Microsoft has always controlled PC software by virtue of their control
over the PC operating system, what about the hardware? It is easy to see that IBM controlled the
PC hardware standard up through 1987. After all, IBM invented the core PC motherboard design,
expansion bus slot architecture (8/16-bit ISA bus), serial and parallel port design, video card
design through VGA and XGA standards, floppy and hard disk interface and controller designs,
power supply design, keyboard interface and design, mouse interface, and even the physical
shapes (form factors) of everything from the motherboard to the expansion cards, power supplies, and system chassis. All these pre-1987 IBM PC, XT and AT system design features are still
influencing modern systems today.
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But to me the real question is what company has been responsible for creating and inventing
new and more recent PC hardware designs, interfaces, and standards? When I ask people that
question, I normally see some hesitation in their response—some people say Microsoft (but they
control the software, not the hardware), some say Compaq or name a few other big name system
manufacturers. Only a few surmise the correct answer—Intel.
I can see why many people don’t immediately realize this; I mean, how many people actually
own an Intel brand PC? No, not just one that says “intel inside” on it (which refers only to the
system having an Intel processor), but a system that was designed and built by Intel or even purchased through them. Believe it or not, I think that many, if not most, people today do have
Intel PCs!
Certainly this does not mean that they have purchased their systems from Intel because it is well
known that Intel does not sell complete PCs direct to end users. You cannot currently order a system from Intel, nor can you purchase an Intel brand system from somebody else. What I am talking about is the motherboard. In my opinion, the single most important part in a PC system is
the motherboard, and I’d say that whoever made your motherboard should be considered the
legitimate manufacturer of your system. Even back when IBM was the major supplier of PCs, they
only made the motherboard, and contracted the other components of the system (power supply,
disk drives, and so on) out to others.
◊◊ See “Motherboards and Buses,” p. 203.
The top tier system manufacturers do make their own motherboards. According to Computer
Reseller News magazine, the top three desktop systems manufacturers for the last several years
have consistently been Compaq, Packard Bell, and IBM. These companies, for the most part, do
design and manufacture their own motherboards, as well as many other system components. In
some cases they even design their own chips and chipset components for their own boards.
Although sales are high for these individual companies, there is a larger overall segment of the
market that can be called the second tier.
In the second tier are companies who do not really manufacture systems, but assemble them
instead. That is, they purchase motherboards, cases, power supplies, disk drives, peripherals, and
so on, and assemble and market the components together as complete systems. Dell, Gateway,
and Micron are some of the larger system assemblers today, but there are hundreds more who can
be listed. In overall total volume, this ends up being the largest segment of the PC marketplace
today. What is interesting about the second tier systems is that, with very few exceptions, you
and I can purchase the same motherboards and other components any of the second tier manufacturers can (although we pay more than they do). We can also assemble a virtually identical
system from scratch ourselves, but that is a story for another chapter, and is covered in Chapter
24, “Building or Upgrading Systems.”
If Gateway, Dell, Micron, and others do not manufacture their own motherboards, who does?
You guessed it—Intel. Not only do those specific companies use pretty much exclusively Intel
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motherboards, if you check around you’ll find today that many, if not most, of the systems on
the market in the second tier come with Intel motherboards. The only place Intel doesn’t dominate is the low-end market Socket 7 type systems, which is mainly because Intel had originally
abandoned the Socket 7 design and the low end market in general. Now they are coming back
strong in the low end PC market with the newer Socket 370 design, with which they intend to
dominate the low end market as well.
I checked a review of 10 different Pentium II systems in the current Computer Shopper magazine,
and I’m not kidding, eight out of the 10 systems they evaluated had Intel motherboards. In fact,
those eight used the exact same Intel motherboard. That means that these systems differ only in
the cosmetics of the exterior case assembly and by what video card, disk drives, keyboards, and so
on the assembler used that week.
The other two systems in the sample review had boards from manufacturers other than Intel, but
even those boards used Intel Pentium II processors and Intel motherboard chipsets, which
together comprise more than 90 percent of the motherboard cost. This review was not an anomaly; it is consistent with what I have been seeing under the hood of mail-order and mainstream
“white box” PC systems for years.
◊◊ See “Pentium II Processors,” p. 162.
◊◊ See “Chipsets,” p. 235.
How and when did this happen? Intel has been the dominant PC processor supplier since IBM
chose the Intel 8088 CPU in the original IBM PC in 1981. By controlling the processor, Intel naturally had control of the chips needed to integrate their processors into system designs. This naturally led Intel into the chipset business. They started their chipset business in 1989 with the
82350 EISA (Extended Industry Standard Architecture) chipset, and by 1993 they had become—
along with the debut of the Pentium processor—the largest volume major motherboard chipset
supplier. Now I imagine them sitting there, thinking that they make the processor and all the
other chips needed to produce a motherboard, so why not just eliminate the middle man and
make the entire motherboard too? The answer to this, and a real turning point in the industry,
came about in 1994 when Intel became the largest-volume motherboard manufacturer in the
world. And they have remained solidly on top ever since. They don’t just lead in this category by
any small margin; in fact, during 1997 Intel made more motherboards than the next eight largest
motherboard manufacturers combined, with sales of more than 30 million boards, worth more
than $3.6 billion! Note that this figure does not include processors or chipsets—only the boards
themselves. These boards end up in the various system assembler brand PCs you and I buy,
meaning that most of us are now essentially purchasing Intel-manufactured systems, no matter
who actually wielded the screwdriver.
Table 2.1 shows the top 10 motherboard manufacturers, ranked by 1997 sales (1998 sales reports
were not available at the time this book was printed).
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Note
These figures reflect sales in millions.
Table 2.1
Top Motherboard Manufacturers (Computer Reseller News)
Motherboard Manufacturer
1997 Sales
1996 Sales
Intel
$3,600
$3,200
Acer
$825
$700
AsusTek
$640
$426
Elitegroup
$600
$600
First International Computer (FIC)
$550
$450
QDI Group
$320
$246
Soyo
$254
$123
Giga-Byte
$237
$165
Micro-Star
$205
$180
Diamond Flower (DFI)
$160
$100
Without a doubt, Intel controls the PC hardware standard because they control the PC motherboard. They not only make the vast majority of motherboards being used in systems today, but
they also supply the vast majority of processors and motherboard chipsets to other motherboard
manufacturers. This means that even if you don’t have an actual Intel motherboard, the motherboard you do have probably has an Intel processor or chipset.
Intel also has a hand in setting several of the more recent PC hardware standards. It was Intel
who originally created the PCI (Peripheral Component Interconnect) local bus interface and the
new AGP (Accelerated Graphics Port) interface for high performance video cards. Intel designed
the ATX motherboard form factor that replaces the (somewhat long in the tooth) IBM-designed
Baby-AT form factor that has been used since the early `80s. Intel also created the NLX motherboard form factor to replace the proprietary and limited LPX design used by many lower-cost systems, which finally brought motherboard upgradability to those systems. Intel also created the
DMI (Desktop Management Interface) for monitoring system hardware functions and the DPMA
(Dynamic Power Management Architecture) and APM (Advanced Power Management) standards
for managing power usage in the PC.
Intel has pushed for advancements in motherboard chipsets; supporting new types of memory
such as EDO (Extended Data Out), SDRAM (Synchronous Dynamic RAM), and RDRAM (Rambus
Dynamic RAM); new and faster bus interfaces; and faster memory access. They are also having a
major effect in the portable market, bringing out special low-power processors, chipsets, and
mobile modules (combining processor and chipset together on a daughterboard) to ease portable
system design and improve functionality and performance. It doesn’t take much to see that Intel
is clearly in as much control of the PC hardware standard as Microsoft is in control of the PC
software standard.
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These days, the Intel processor and chipsets are so ubiquitous that these components are being
reverse-engineered, and so called “Intel-compatible” versions are being produced. Companies
such as AMD, Cyrix, and others have a variety of processors, which are direct pin-compatible
replacements for Intel processors; furthermore, some chipset manufacturers have even produced
pin for pin copies of Intel chipsets.
Whoever controls the operating system controls the software for the PC, and whoever controls
the processor—and therefore the motherboard—controls the hardware. Because it seems to be a
Microsoft and Intel combination for the software and hardware control in the PC today, it is no
wonder the modern PC is often called a “Wintel” system.
PC 9x Specifications
Even though Intel has full control of PC hardware, Microsoft recognizes their power over the PC
from the operating system perspective and has been releasing a series of documents called the
“PC 9x Design Guides” (where 9x designates the year) as a set of standard specifications to guide
both hardware and software developers who are creating products that work with Windows. The
requirements in these guides are part of Microsoft’s “Designed for Windows” logo requirement. In
other words, if you produce either a hardware or software product and you want the official
“Designed for Windows” logo to be on your box, your product has to meet the PC 9x minimum
requirements.
Following are the documents that have been produced so far:
■ Hardware Design Guide for Microsoft Windows 95
■ Hardware Design Guide Supplement for PC 95
■ PC 97 Hardware Design Guide
■ PC 98 System Design Guide
■ PC 99 System Design Guide
■ PC 2000 System Design Guide
All these documents are available for download from Microsoft’s Web site, and they have also
been available as published books from Microsoft Press.
These system design guides present information for engineers who build personal computers,
expansion cards, and peripheral devices that are to be used with Windows 95, 98, and NT operating systems. The requirements and recommendations for PC design in these guides form the basis
for the requirements of the “Designed for Microsoft Windows” logo program for hardware that
Microsoft sponsors.
These guides include requirements for basic (desktop and mobile) systems, workstations, and
even entertainment PCs. They also address Plug-and-Play device configuration and power management in PC systems, requirements for universal serial bus (USB) and IEEE 1394, and new
devices supported under Windows, including new graphics and video device capabilities, DVD,
scanners and digital cameras, and other devices.
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Note
Note that these guides do not mean anything directly for the end user; instead, they are meant to be guides for PC
manufacturers to build their systems. As such, they are only recommendations, and they do not have to be followed
to the letter. In some ways they are a market control tool for Intel and Microsoft to further wield their influence on
PC hardware and software. In reality, the market often dictates that some of these recommendations are disregarded, which is one reason why they continue to evolve with new versions year after year.
System Types
PCs can be broken down into many different categories. I like to break them down in two different ways—one by the type of software they can run, the other by the motherboard host bus, or
processor bus design and width. Because this book concentrates mainly on hardware, let’s look at
that first.
When a processor reads data, the data moves into the processor via the processor’s external data
bus connection. The processor’s data bus is directly connected to the processor host bus on the
motherboard. The processor data bus or host bus is also sometimes referred to as the local bus
because it is local to the processor that is connected directly to it. Any other devices that are connected to the host bus essentially appear as if they are directly connected to the processor as well.
If the processor has a 32-bit data bus, the motherboard must be wired to have a 32-bit processor
host bus. This means that the system can move 32-bits worth of data into or out of the processor
in a single cycle.
◊◊ See “Data Bus,” p. 50.
Different processors have different data bus widths, and the motherboards that are designed to
accept them require a processor host bus with a matching width. Table 2.2 lists all the Intel
processors and their data bus widths.
Table 2.2
Intel Processors and Their Data Bus Widths
Processor
Data Bus Width
8088
8-bit
8086
16-bit
286
16-bit
386SX
16-bit
386DX
32-bit
486 (all)
32-bit
Pentium
64-bit
Pentium MMX
64-bit
Pentium Pro
64-bit
Pentium Celeron/II/III
64-bit
Pentium II/III Xeon
64-bit
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A common misconception arises in discussions of processor widths. Although the Pentium
processors all have 64-bit data bus widths, their internal registers are only 32 bits wide, and they
process 32-bit commands and instructions. Thus, from a software point of view, all chips from
the 386 to the Pentium III have 32-bit registers and execute 32-bit instructions. From the electronic or physical perspective, these 32-bit software capable processors have been available in
physical forms with 16-bit (386SX), 32-bit (386DX, 486), and 64-bit (Pentium) data bus widths.
The data bus width is the major factor in motherboard and memory system design because it dictates how many bits move in and out of the chip in one cycle.
◊◊ See “Internal Registers,” p. 51.
The future P7 processor, code-named Merced, will have a new Intel Architecture 64-bit (IA-64)
instruction set, but it will also process the same 32-bit instructions as 386 through Pentium
processors do. It is not known whether Merced will have a 64-bit data bus like the Pentium or
whether it will include a 128-bit data bus.
◊◊ See “Processor Specifications,” p. 39.
From Table 2.2 you can see that 486 systems have a 32-bit processor bus, which means that any
486 motherboard would have a 32-bit processor host bus. Pentium processors, whether they are
the original Pentium, Pentium MMX, Pentium Pro, or even the Pentium II and III, all have 64-bit
data busses. This means that Pentium motherboards have a 64-bit processor host bus. You cannot
put a 64-bit processor on a 32-bit motherboard, which is one reason that 486 motherboards cannot accept true Pentium processors.
As you can see from this table, we can break systems down into the following hardware categories:
■ 8-bit
■ 16-bit
■ 32-bit
■ 64-bit
What is interesting is that besides the bus width, the 16- through 64-bit systems are remarkably
similar in basic design and architecture. The older 8-bit systems are very different, however. This
gives us two basic system types, or classes, of hardware:
■ 8-bit (PC/XT-class) systems
■ 16/32/64-bit (AT-class) systems
PC stands for personal computer, XT stands for an eXTended PC, and AT stands for an advanced
technology PC. The terms PC, XT, and AT, as they are used here, are taken from the original IBM
systems of those names. The XT was basically a PC system that included a hard disk for storage in
addition to the floppy drives found in the basic PC system. These systems had an 8-bit 8088
processor and an 8-bit Industry Standard Architecture (ISA) Bus for system expansion. The bus is
the name given to expansion slots in which additional plug-in circuit boards can be installed.
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The 8-bit designation comes from the fact that the ISA Bus found in the PC/XT class systems can
send or receive only eight bits of data in a single cycle. The data in an 8-bit bus is sent along
eight wires simultaneously, in parallel.
◊◊ See “The ISA Bus,” p. 283.
16-bit and greater systems are said to be AT-class, which indicates that they follow certain standards, and that they follow the basic design first set forth in the original IBM AT system. AT is
the designation IBM applied to systems that first included more advanced 16-bit (and later, 32and 64-bit) processors and expansion slots. AT-class systems must have a processor that is
compatible with Intel 286 or higher processors (including the 386, 486, Pentium, Pentium Pro,
and Pentium II processors), and they must have a 16-bit or greater system bus. The system bus
architecture is central to the AT system design, along with the basic memory architecture,
Interrupt ReQuest (IRQ), DMA (Direct Memory Access), and I/O port address design. All AT-class
systems are similar in the way these resources are allocated and how they function.
The first AT-class systems had a 16-bit version of the ISA Bus, which is an extension of the original 8-bit ISA Bus found in the PC/XT-class systems. Eventually, several expansion slot or bus
designs were developed for AT-class systems, including those in the following list:
■ 16-bit ISA bus
■ 16/32-bit Extended ISA (EISA) bus
■ 16/32-bit PS/2 Micro Channel Architecture (MCA) bus
■ 16-bit PC-Card (PCMCIA) bus
■ 32-bit Cardbus (PCMCIA) bus
■ 32-bit VESA Local (VL) bus
■ 32/64-bit Peripheral Component Interconnect (PCI) bus
■ 32-bit Accelerated Graphics Port (AGP)
A system with any of these types of expansion slots is by definition an AT-class system, regardless
of the actual Intel or Intel-compatible processor that is used. AT-type systems with 386 or higher
processors have special capabilities that are not found in the first generation of 286-based ATs.
The 386 and higher systems have distinct capabilities regarding memory addressing, memory
management, and possible 32- or 64-bit wide access to data. Most systems with 386DX or higher
chips also have 32-bit bus architectures to take full advantage of the 32-bit data transfer capabilities of the processor.
Most PC systems today incorporate 16-bit ISA slots for backward compatibility and lower function adapters, and PCI slots for truly high performance adapters. Most portable systems use PCCard and Cardbus slots in the portable unit, and ISA and PCI slots in optional docking stations.
Chapter 4, “Motherboards and Buses,” contains a great deal of in-depth information on these and
other PC system buses, including technical information such as pinouts, performance specifications, and bus operation and theory.
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Table 2.3 summarizes the primary differences between the older 8-bit (PC/XT) systems and a
modern AT system. This information distinguishes between these systems and includes all IBM
and compatible models.
Table 2.3
Differences Between PC/XT and AT Systems
System Attributes
(8-bit) PC/XT Type
(16/32/64-bit) AT Type
Supported processors
All x86 or x88
286 or higher
Processor modes
Real
Real/ Protected/Virtual Real
Software supported
16-bit only
16- or 32-bit
Bus slot width
8-bit
16/32/64-bit
Slot type
ISA only
ISA, EISA, MCA, PC-Card, Cardbus, VL-Bus, PCI
Hardware interrupts
8 (6 usable)
16 (11 usable)
DMA channels
4 (3 usable)
8 (7 usable)
Maximum RAM
1MB
16MB/4GB or more
Floppy controller speed
250 Kbit/sec
250/300/500/1,000 Kbit/sec
Standard boot drive
360KB or 720KB
1.2MB/1.44MB/2.88MB
Keyboard interface
Unidirectional
Bidirectional
CMOS memory/clock
None standard
MC146818-compatible
Serial-port UART
8250B
16450/16550A
The easiest way to identify a PC/XT (8-bit) system is by the 8-bit ISA expansion slots. No matter
what processor or other features the system has, if all the slots are 8-bit ISA, the system is a
PC/XT. AT (16-bit plus) systems can be similarly identified—they have 16-bit or greater slots of
any type. These can be ISA, EISA, MCA, PC-card (formerly PCMCIA), Cardbus, VL-Bus, or PCI.
Using this information, you can properly categorize virtually any system as a PC/XT type or an
AT type. There really have been no PC/XT type (8-bit) systems manufactured for many years.
Unless you are in a computer museum, virtually every system you encounter today is based on
the AT type design.
System Components
A modern PC is both simple and complicated. It is simple in the sense that over the years many
of the components used to construct a system have become integrated with other components
into fewer and fewer actual parts. It is complicated in the sense that each part in a modern system performs many more functions than did the same types of parts in older systems.
This section briefly examines all the components in a modern PC system. Each of these components is discussed further in later chapters.
Here are the components needed to assemble a basic modern PC system:
■ Motherboard
■ Processor
■ Memory (RAM)
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■ Case (chassis)
■ Power supply
■ Floppy drive
■ Hard disk
■ CD-ROM, CD-R, or DVD-ROM drive
■ Keyboard
■ Mouse
■ Video card
■ Monitor (display)
■ Sound card
■ Speakers
Motherboard
The motherboard is the core of the system. It really is the PC—everything else is connected to it,
and it controls everything in the system. Motherboards are available in several different shapes or
form factors. The motherboard usually contains the following individual components:
■ Processor socket (or slot)
■ Processor voltage regulators
■ Motherboard chipset
■ Level 2 cache (normally found in the CPU today)
■ Memory SIMM or DIMM sockets
■ Bus slots
■ ROM BIOS
■ Clock/CMOS battery
■ Super I/O chip
The chipset contains all the primary circuitry that makes up the motherboard; in essence, the
chipset is the motherboard. The chipset controls the CPU or processor bus, the L2 cache and
main memory, the PCI (Peripheral Component Interconnect) bus, the ISA (Industry Standard
Architecture) bus, system resources, and more. If the processor represents the engine of your system, the chipset represents the chassis in which the engine is installed. As such, the chipset dictates the primary features and specifications of your motherboard, including what types of
processors, memory, expansion cards, disk drives, and so on the system supports.
Note that most newer (Pentium Celeron/II/III class) systems include the L2 cache inside the
processor rather than on the motherboard. In the newest and best designs, the L2 cache is actually a part of the processor die just like the L1 cache, whereas in others it is simply a separate
chip (or chips) in the processor module.
The chipset plays a big role in determining what sorts of features a system can support. For example, which processors you can use, which types and how much memory you can install, what
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speeds you can run the machine, and what types of system buses your system can support are all
tied in to the motherboard chipset. The ROM BIOS contains the initial POST (Power-On Self Test)
program, bootstrap loader (which loads the operating system), drivers for items that are built into
the board (the actual BIOS code), and usually a system setup program (often called CMOS setup)
for configuring the system. Motherboards are covered in detail in Chapter 4.
Processor
The processor is often thought of as the “engine” of the computer. Also called the CPU (Central
Processing Unit), it is the single most important chip in the system because it is the primary
circuit that carries out the program instructions of whatever software is being run. Modern
processors contain literally millions of transistors, etched onto a tiny square of silicon called a
die, which is about the size of your thumbnail. The processor has the distinction of being one of
the most expensive parts of most computers, even though it is also one of the smallest parts. In
most modern systems, the processor costs from two to ten times more than the motherboard it is
plugged into.
Microprocessors are covered in detail in Chapter 3, “Microprocessor Types and Specifications.”
Memory (RAM)
The system memory is often called RAM (for Random Access Memory). This is the primary memory, which holds all the programs and data the processor is using at a given time. RAM requires
power to maintain storage, so when you turn off the computer everything in RAM is cleared;
when you turn it back on the memory must be reloaded with programs for the processor to run.
The initial programs for the processor come from a special type of memory called ROM (Read
Only Memory), which is not erased when the power to the system is turned off.
The ROM contains instructions to get the system to load or boot an operating system and other
programs from one of the disk drives into the main RAM memory so that the system can run
normally and perform useful work. Newer operating systems allow several programs to run at one
time, with each program or data file that is loaded using some of the main memory. Generally,
the more memory your system has, the more programs you can run simultaneously.
Memory is normally purchased and installed in a modern system in SIMM (Single Inline Memory
Module) or DIMM (Dual Inline Memory Module) form. Formerly very expensive, memory prices
have dropped recently, significantly reducing the cost of memory as compared to other parts of
the system. Even so, the cost of the recommended amount of memory for a given system is usually equal or greater than that of the motherboard.
Memory is covered in detail in Chapter 6, “Memory.”
Case (Chassis)
The case is the frame or chassis that houses the motherboard, power supply, disk drives, adapter
cards, and any other physical components in the system. There are several different styles of cases
available, from small or slim versions that sit horizontally on a desktop to huge tower types that
stand vertically on the floor, and even some that are designed to be rackmounted for industrial
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use. In addition to the physical styles, different cases are designed to accept different form factor
motherboards and power supplies. Some cases have features that make installing or removing
components easy, such as a screwless design that requires no tools to disassemble, side open panels or trays that allow easy motherboard access, removable cages or brackets that give easy access
to disk drives, and so on. Some cases include additional cooling fans for heavy duty systems, and
some are even available with air filters that ensure that the interior will remain clean and dust
free. Most cases include a power supply, but you can also purchase bare cases and power supplies
separately.
The case is covered in detail in Chapter 21, “Power Supply and Chassis/Case.”
Power Supply
The power supply is what feeds electrical power to every single part in the PC. As such, it has a
very important job, but it is one of the least glamorous parts of the system so it receives little
attention. Unfortunately, this often means that it is one of the components that is most skimped
on when a system is constructed. The main function of the supply is to convert the 110v AC wall
current into the 3.3v, 5v, or 12fv power that the system requires for operation.
The power supply is covered in detail in Chapter 21.
Floppy Disk Drive
The floppy drive is a simple, inexpensive, low capacity removable media magnetic storage device.
For many years floppy disks were the primary medium for software distribution and system
backup. However, with the advent of CD-ROM and DVD-ROM discs as the primary method of
installing or loading new software in a system, and with inexpensive high capacity tape drives for
backup, the floppy drive is not used very often in most modern systems, except perhaps by a system builder, installer, or technician. Because the floppy drive is the first device from which a PC
attempts to boot, it is still the primary method that is used for loading initial operating systems’
startup software and core hardware diagnostics. Recent advancements in technology have created
new types of floppy drives with up to 120MB or more of storage, making the drive much more
usable for temporary backups or for moving files from system to system.
Floppy disk drives are covered in detail in Chapter 11, “Floppy Disk Storage.”
Hard Disk Drive
The hard disk is the primary archival storage memory for the system. It contains copies of all programs and data that are not currently active in main memory. A hard drive is so named because
it consists of spinning platters of aluminum or ceramic that are coated with a magnetic medium.
Hard drives can be created with many different storage capacities, depending on the density, size,
and number of platters. Most desktop systems today use drives with 3 1/2-inch platters, whereas
most laptop or notebook computers use 2 1/2-inch platter drives.
Hard disk drives are also covered in detail in Chapter 10, “Hard Disk Storage.”
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CD-ROM Drive
CD- (Compact Disc) and DVD- (Digital Versatile Disc) ROM (Read Only Memory) drives are relatively high capacity removable media optical drives. They are primarily a read-only medium,
which means the drives can only read information, and the data on the discs cannot altered or
rewritten. There are writable or rewritable versions of the discs and drives available, but they are
much more expensive than their read-only counterparts, and therefore are not included standard
in most PCs. CD-ROM and DVD-ROM are the most popular media for distributing software or
large amounts of data because they are very inexpensive when produced in quantity and they
can hold a great deal of information.
CD-ROM drives are covered in detail in Chapter 13, “Optical Storage.”
Keyboard
The keyboard is the primary device on a PC that is used by a human being to communicate with
and control a system. Keyboards are available in a large number of different languages, layouts,
sizes, shapes, and with numerous special features or characteristics. One of the best features of
the PC as designed by IBM is that it was one of the first personal computers to use a detached
keyboard. Most systems prior to the PC had the keyboard as an integral part of the system chassis, which severely limited flexibility. Because the PC uses a detached keyboard with a standardized connector and signal design, in most cases it is possible to connect any PC compatible
keyboard you want to your system, which gives you the freedom to choose the one that suits you
best.
Keyboards are covered in detail in Chapter 17, “Input Devices.”
Mouse
With the advent of computer operating systems that used a Graphical User Interface (GUI), it
became necessary to have a device that enabled a user to point at or select items that were shown
on the screen. Although there are many different types of pointing devices on the market today,
the first and most popular device for this purpose is the mouse. By moving the mouse across a
desk or tabletop, a corresponding pointer can be moved across the computer screen, allowing
items to be more easily selected or manipulated than they can with a keyboard alone. Standard
mice, as used on PCs, have two buttons: one for selecting items under the pointer, and the other
for activating menus. Mice are also available with a third button, a wheel, or a stick, which can
be used to scroll the display or for other special functions.
The mouse is covered in detail in Chapter 17.
Video Card
The video card controls the information you see on the monitor. All video cards have four basic
parts: a video chip or chipset, Video RAM, a DAC (Digital to Analog Converter), and a BIOS. The
video chip actually controls the information on the screen by writing data to the video RAM.
The DAC reads the video RAM and converts the digital data there into analog signals to drive the
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monitor. The BIOS holds the primary video driver that allows the display to function during boot
time and at a DOS prompt in basic text mode. More enhanced drivers are then usually loaded
from disk to enable advanced video modes for Windows or applications software.
Video cards are covered in detail in Chapter 15, “Video Hardware.”
Monitor (Display)
In most systems, the monitor is housed in its own protective case, separate from the system case
and chassis. In portable systems and some low-cost PCs, however, the monitor is built into the
system case. Monitors are generally classified by three major criteria: diagonal size in inches, resolution in pixels, and refresh rate in hertz (Hz). Desktop monitors usually range from 14” to 21”
diagonal measure (although as you will see in Chapter 8, “The SCSI Interface,” the actual viewable area is smaller than the advertised measure). LCD monitors in portable systems range from
11” to 14”. Resolution ranges from 640×480 pixels (horizontal measurement first, and then vertical) to 1600×1200 pixels. Each pixel in the monitor is made up of a trio of dots, one each for the
colors red, blue, and green. An average monitor is capable of refreshing 60 times per second
(60Hz), whereas higher quality monitors might refresh at 100Hz. The refresh rate measures how
often the display of the screen is redrawn from the contents of the video adapter memory. Both
the resolution and refresh rate of the monitor are tied to the capability of the system video
adapter. Most monitors are capable of supporting several different resolutions and refresh rates
(with the common exception of LCD screens in portables).
Monitors are covered in detail in Chapter 15.
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3
35 35
Microprocessor
Types and
Specifications
SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE
CHAPTER 3
Processor Specifications
SSE (Streaming SIMD Extensions)
Dual Independent Bus (DIB) Architecture
Processor Manufacturing
PGA Chip Packaging
Single Edge Contact (SEC) and Single Edge Processor (SEP)
Packaging
Processor Sockets
Processor Slots
CPU Operating Voltages
Heat and Cooling Problems
Intel-Compatible Processors (AMD and Cyrix)
P1 (086) First-Generation Processors
P2 (286) Second-Generation Processors
P3 (386) Third-Generation Processors
P4 (486) Fourth-Generation Processors
P5 (586) Fifth-Generation Processors
Intel P6 (686) Sixth-Generation Processors
P7 (786) Seventh-Generation Processors
Processor Troubleshooting Techniques
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Microprocessors
The brain or engine of the PC is the processor (sometimes called microprocessor), or Central
Processing Unit (CPU). The CPU performs the system’s calculating and processing. The processor
is easily the most expensive single component in the system, costing up to four or more times
greater than the motherboard it plugs into. Intel is generally credited with creating the first
microprocessor in 1971 with the introduction of a chip called the 4004. Today they have almost
total control over the processor market, at least for PC systems. This means that all
PC-compatible systems use either Intel processors or Intel-compatible processors from a handful
of competitors (such as AMD or Cyrix).
Intel’s dominance in the processor market had not always been assured. Although they are generally credited with inventing the processor and introducing the first one on the market, by the
late 70s the two most popular processors for PCs were not from Intel (although one was a clone
of an Intel processor). Personal computers of that time primarily used the Z-80 by Zilog and the
6502 by MOS Technologies. The Z-80 was noted for being an improved and less expensive clone
of the Intel 8080 processor, similar to the way companies today such as AMD, Cyrix, IDT, and
Rise Technologies have cloned Intel’s Pentium processors.
Back then I had a system containing both of those processors, consisting of a 1MHz (yes, that’s
one as in 1MHz!) 6502-based Apple main system with a Microsoft Softcard (Z-80 card) plugged
into one of the slots. The Softcard contained a 2MHz Z-80 processor. This allowed me to run software for both types of processors on the one system. The Z-80 was used in systems of the late 70s
and early 80s that ran the CP/M operating system, while the 6502 was best known for its use in
the early Apple computers (before the Mac).
The fate of both Intel and Microsoft were dramatically changed in 1981 when IBM introduced
the IBM PC, which was based on a 4.77MHz Intel 8088 processor running the Microsoft Disk
Operating System (DOS) 1.0. Since that fateful decision was made, PC-compatible systems have
used a string of Intel or Intel compatible processors, each new one capable of running the software of the processor before it, from the 8088 to the current Pentium III. The following sections
cover the different types of processor chips that have been used in personal computers since the
first PC was introduced almost two decades ago. These sections provide a great deal of technical
detail about these chips and explain why one type of CPU chip can do more work than another
in a given period of time.
Pre-PC Microprocessor History
It is interesting to note that the microprocessor had only existed for 10 years prior to the creation
of the PC! The microprocessor was invented by Intel in 1971. The PC was created by IBM in
1981. Now nearly 20 years later, we are still using systems based on the design of that first PC
(and mostly backward compatible with it). The processors powering our PCs today are still backward compatible with the one selected by IBM in 1981.
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The story of the development of the first microprocessor, the Intel 4004, can be read in Chapter
1, “Personal Computer Background.” The 4004 processor was introduced on November 15, 1971,
and originally ran at a clock speed of 108KHz (108,000 cycles per second, or 0.108MHz). The
4004 contained 2,300 transistors and was built on a 10 micron process. This means that each
line, trace, or transistor could be spaced about 10 microns (millionths of a meter) apart. Data was
transferred four bits at a time, and the maximum addressable memory was only 640 bytes. The
4004 was designed for use in a calculator, but proved to be useful for many other functions
because of its inherent programmability.
In April 1972, Intel released the 8008 processor, which originally ran at a clock speed of 200KHz
(0.2MHz). The 8008 processor contained 3,500 transistors and was built on the same 10 micron
process as the previous processor. The big change in the 8008 was that it had an 8-bit data bus,
which meant it could move data 8 bits at a time—twice as much as the previous chip. It could
also address more memory, up to 16KB. This chip was primarily used in dumb terminals and
general-purpose calculators.
The next chip in the lineup was the 8080, introduced in April 1974, running at a clock rate of
2MHz. Due mostly to the faster clock rate, the 8080 processor had 10 times the performance of
the 8008. The 8080 chip contained 6,000 transistors and was built on a 6 micron process. Like
the previous chip, the 8080 had an 8-bit data bus, so it could transfer 8 bits of data at a time. The
8080 could address up to 64KB of memory, significantly more than the previous chip.
It was the 8080 that helped start the PC revolution, as this was the processor chip used in what is
generally regarded as the first personal computer, the Altair 8800. The CP/M operating system
was written for the 8080 chip, and Microsoft was founded and delivered their first product:
Microsoft BASIC for the Altair. These initial tools provided the foundation for a revolution in
software because thousands of programs were written to run on this platform.
In fact, the 8080 became so popular that it was cloned. A company called Zilog formed in late
1975, joined by several ex-Intel 8080 engineers. In July of 1976, they released the Z-80 processor,
which was a vastly improved version of the 8080. It was not pin compatible, but instead combined functions such as the memory interface and RAM refresh circuitry, which allowed cheaper
and simpler systems to be designed. The Z-80 also incorporated a superset of 8080 instructions,
meaning it could run all 8080 programs. It also included new instructions and new internal registers, so software that was designed for the Z-80 would not necessarily run on the older 8080. The
Z-80 ran initially at 2.5MHz (later versions ran up to 10MHz), and contained 8,500 transistors.
The Z-80 could access 64KB of memory.
Radio Shack selected the Z-80 for the TRS-80 Model 1, their first PC. The chip was also the first to
be used by many pioneering systems including the Osborne and Kaypro machines. Other companies followed suit, and soon the Z-80 was the standard processor for systems running the CP/M
operating system and the popular software of the day.
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Intel released the 8085, their follow up to the 8080, in March of 1976. Even though it pre-dated
the Z-80 by several months, it never achieved the popularity of the Z-80 in personal computer
systems. It was popular as an embedded controller, finding use in scales and other computerized
equipment. The 8085 ran at 5MHz and contained 6,500 transistors. It was built on a 3 micron
process and incorporated an 8-bit data bus.
Along different architectural lines, MOS Technologies introduced the 6502 in 1976. This chip was
designed by several ex-Motorola engineers who had worked on Motorola’s first processor, the
6800. The 6502 was an 8-bit processor like the 8080, but it sold for around $25, whereas the 8080
cost about $300 when it was introduced. The price appealed to Steve Wozniak who placed the
chip in his Apple I and Apple II designs. The chip was also used in systems by Commodore and
other system manufacturers. The 6502 and its successors were also used in computer games,
including the original Nintendo Entertainment System (NES) among others. Motorola went on to
create the 68000 series, which became the basis for the Apple Macintosh line of computers.
Today those systems use the PowerPC chip, also by Motorola, and a successor to the original
68000 series.
All these previous chips set the stage for the first PC chips. Intel introduced the 8086 in June
1978. The 8086 chip brought with it the original x86 instruction set that is still present on x86compatible chips such as the Pentium III. A dramatic improvement over the previous chips, the
8086 was a full 16-bit design with 16-bit internal registers and a 16-bit data bus. This meant that
it could work on 16-bit numbers and data internally and also transfer 16-bits at a time in and out
of the chip. The 8086 contained 29,000 transistors and initially ran at up to 5MHz. The chip also
used 20-bit addressing, meaning it could directly address up to 1MB of memory. Although not
directly backward compatible with the 8080, the 8086 instructions and language was very similar
and allowed older programs to be ported over quickly to run. This later proved important to help
jumpstart the PC software revolution with recycled CP/M (8080) software.
Although the 8086 was a great chip, it was expensive at the time and more importantly required
an expensive 16-bit support chips and board design. To help bring costs down, in 1979, Intel
released a crippled version of the 8086 called the 8088. The 8088 processor used the same internal core as the 8086, had the same 16-bit registers, and could address the same 1MB of memory,
but the external data bus was reduced to 8 bits. This allowed support chips from the older 8-bit
8085 to be used, and far less expensive boards and systems could be made. It is for these reasons
that IBM chose the crippled chip, the 8088, for the first PC.
This decision would affect history in several ways. The 8088 was fully software compatible with
the 8086, so it could run 16-bit software. Also, because the instruction set was very similar to the
previous 8085 and 8080, programs written for those older chips could be quickly and easily modified to run. This allowed a large library of programs to be quickly released for the IBM PC, thus
helping it become a success. The overwhelming blockbuster success of the IBM PC left in its wake
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the legacy of requiring backward compatibility with it. In order to maintain the momentum,
Intel has pretty much been forced to maintain backward compatibility with the 8088/8086 in
most of the processors they have released since then.
In some ways the success of the PC, and the Intel architecture it contains, has limited the growth
of the personal computer. In other ways, however, its success has caused a huge number of programs, peripherals, and accessories to be developed, and the PC to become a de facto standard in
the industry. The original 8088 processor used in the first PC contained close to 30,000 transistors and ran at less than 5MHz. The most recent processors from Intel contain close to 30 million
transistors and run at over 500MHz. Intel has already demonstrated processors running at 1GHz.
According to Moore’s Law, these will be commonplace in only a few years, along with transistor
counts in the hundreds of millions.
Processor Specifications
Many confusing specifications often are quoted in discussions of processors. The following sections discuss some of these specifications, including the data bus, address bus, and speed. The
next section includes a table that lists the specifications of virtually all PC processors.
Processors can be identified by two main parameters: how wide they are and how fast they are.
The speed of a processor is a fairly simple concept. Speed is counted in megahertz (MHz), which
means millions of cycles per second—and faster is better! The width of a processor is a little more
complicated to discuss because there are three main specifications in a processor that are
expressed in width. They are
■ Data input and output bus
■ Internal registers
■ Memory address bus
Table 3.1 lists the primary specifications for the Intel family of processors used in IBM and compatible PCs. Table 3.2 lists the Intel compatible processors from AMD, Cyrix, Nexgen, IDT, and
Rise. The following sections explain these specifications in detail.
Note that most Pentium II and III processors include 512KB of 1/2-core speed L2 cache on the
processor card, while the Xeon includes 512KB, 1MB, or 2MB of full-core speed L2 cache. The
Celeron and Pentium II PE processors, as well as the K6-3 from AMD, all include on-die L2 cache,
which runs at the full core speed of the processor. Most all future processors will contain the L2
cache directly in the CPU die and run it at full core speed.
The transistor count figures do not include the standard 256KB or 512KB L2 cache built in to the
Pentium Pro and Pentium II CPU packages. The L2 cache contains an additional 15.5 (256KB), 31
(512KB), or optionally 62 million (1MB) transistors!
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Intel Processor Specifications
Voltage
Internal
Register
Size
Data
Bus
Width
Max.
Memory
L1
Cache
1x
5v
16-bit
8-bit
1MB
-
8086
286
386SX
386SL
1x
1x
1x
1x
5v
5v
5v
3.3v
16-bit
16-bit
32-bit
32-bit
16-bit
16-bit
16-bit
16-bit
1MB
16MB
16MB
16MB
0KB1
386DX
486SX
486SX2
487SX
486DX
486SL2
486DX2
486DX4
486Pentium OD
1x
1x
2x
1x
1x
1x
2x
2-3x
2.5x
5v
5v
5v
5v
5v
3.3v
5v
3.3v
5v
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
4GB
4GB
4GB
4GB
4GB
4GB
4GB
4GB
4GB
8KB
8KB
8KB
8KB
8KB
8KB
16KB
2×16KB
Pentium
Pentium
Pentium
Pentium
512KB
1MB
Pentium
Pentium
Pentium
Pentium
Pentium
1MB
2MB
Pentium
Pentium
1MB
2MB
60/66
75-200
MMX
Pro
1x
1.5-3x
1.5-4.5x
2-3x
5v
3.3-3.5v
1.8-2.8v
3.3v
32-bit
32-bit
32-bit
32-bit
64-bit
64-bit
64-bit
64-bit
4GB
4GB
4GB
64GB
2×8KB
2×8KB
2×16KB
2×8KB
II
II
II
II
II
3.5-4.5x
3.5-4.5x
3.5-7x
3.5-6x
4-4.5x
1.8-2.8v
1.8-2.8v
1.8-2v
1.6v
1.8-2.8v
32-bit
32-bit
32-bit
32-bit
32-bit
64-bit
64-bit
64-bit
64-bit
64-bit
64GB
64GB
64GB
64GB
64GB
2×16KB
2×16KB
2×16KB
2×16KB
2×16KB
4.5-6x
5-6x
1.8-2v
1.8-2v
32-bit
32-bit
64-bit
64-bit
64GB
64GB
2×16KB
2×16KB
Data
Bus
Width
Max.
Memory
L1
Cache
64-bit
64-bit
64-bit
64-bit
64-bit
64-bit
64-bit
64-bit
64-bit
64-bit
4GB
4GB
4GB
4GB
4GB
4GB
4GB
4GB
4GB
4GB
16+8KB
2×32KB
2×32KB
2×32KB
16KB
64KB
2×16KB
2×32KB
2×32KB
2×8KB
Processor
CPU
Clock
8088
MMX
Celeron
Celeron
PE3
Xeon
III
III Xeon
Table 3.2
Intel Compatible Processors
Processor
CPU
Clock
Voltage
Internal
Register
Size
AMD K5
AMD-K6
AMD-K6-2
AMD-K6-3
Cyrix 6x86
Cyrix 6x86MX/MII
Nexgen Nx586
IDT Winchip
IDT Winchip2/2A
Rise mP6
1.5-1.75x
2.5-4.5x
3.5-5x
4-5x
2x
2-3.5x
2x
3-4x
2.33-4x
2-3.5x
3.5v
2.2-3.2v
2.2-2.4v
2.2-2.4v
2.5-3.5v
2.9v
4v
3.3-3.5v
3.3-3.5v
2.8v
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
32-bit
FPU = Floating-Point Unit (internal math coprocessor)
WT = Write-Through cache (caches reads only)
WB = Write-Back cache (caches both reads and writes)
Bus = Processor external bus speed (motherboard speed)
Core = Processor internal core speed (CPU speed)
MMX = Multimedia extensions, 57 additional instructions for graphics and sound processing
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L1
Cache
Type
L2
Cache
L2
Cache
Speed
Integral
FPU
Multimedia
Instructions
No. of
Transistors
Date
Introduced
-
-
-
-
-
29,000
June ‘79
WT
-
Bus
Bus
-
-
29,000
134,000
275,000
855,000
June ‘78
Feb. ‘82
June ‘88
Oct. ‘90
WT
WT
WT
WT
WT
WT
WT
WB
-
Bus
Bus
Bus
Bus
Bus
Bus
Bus
Bus
Bus
Yes
Yes
Opt.
Yes
Yes
Yes
-
275,000
1.185M
1.185M
1.2M
1.2M
1.4M
1.2M
1.6M
3.1M
Oct. ‘85
April ‘91
April ‘94
April ‘91
April ‘89
Nov. ‘92
March ‘92
Feb. ‘94
Jan. ‘95
WB
WB
WB
WB
256KB
Bus
Bus
Bus
Core
Yes
Yes
Yes
Yes
MMX
-
3.1M
3.3M
4.5M
5.5M
March ‘93
Oct. ‘94
Jan. ‘97
Nov. ‘95
WB
WB
WB
WB
WB
512KB
0KB
128KB
256KB
512KB
1/2 Core
Core
Core
Core
Yes
Yes
Yes
Yes
Yes
MMX
MMX
MMX
MMX
MMX
7.5M
7.5M
19M
27.4M
7.5M
May ‘97
April ‘98
Aug. ‘98
Jan. ‘99
April ‘98
WB
WB
512KB
512KB
1/2 Core
Core
Yes
Yes
SSE
SSE
9.5M
9.5M
Feb. ‘99
March ‘99
L1
Cache
Type
L2
Cache
L2
Cache
Speed
Integral
FPU
Multimedia
Instructions
No. of
Transistors
Date
Introduced
WB
WB
WB
WB
WB
WB
WB
WB
WB
WB
256KB
-
Bus
Bus
Bus
Core
Bus
Bus
Bus
Bus
Bus
Bus
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
MMX
3DNow
3DNow
MMX
MMX
3DNow
MMX
4.3M
8.8M
9.3M
21.3M
3M
6.5M
3.5M
5.4M
5.9M
3.6M
March ‘96
April ‘97
May ‘98
Feb. ‘99
Feb. ‘96
May ‘97
March ‘94
Oct. ‘97
Sept. ‘98
Oct. ‘98
41
3DNow = MMX plus 21 additional instructions for graphics and sound processing
SSE = Streaming SIMD (Single Instruction Multiple Data) Extensions, MMX plus 70 additional instructions for
graphics and sound processing
1 The 386SL contains an integral-cache controller, but the cache memory must be provided outside the chip.
2 Intel later marketed SL Enhanced versions of the SX, DX, and DX2 processors. These processors were available in both 5v and 3.3v versions and included power-management capabilities.
3 The Enhanced mobile PII has on-die L2 cache similar to the Celeron.
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Note
Note in Table 3.1, that the Pentium Pro processor includes 256KB, 512KB, or 1MB of full core speed L2 cache in
a separate die within the chip. The Pentium II/III processors include 512KB of 1/2 core speed L2 cache on the
processor card. The Celeron and Pentium II PE processors include full core speed L2 cache integrated directly
within the processor die.
The transistor count figures do not include the external (off-die) 256KB, 512KB, 1MB, or 2MB L2 cache built in to
the Pentium Pro and Pentium II/III or Xeon CPU packages. The external L2 cache contains an additional 15.5
(256KB), 31 (512KB), 62 million (1MB), or 124 million (2MB) transistors!
Processor Speed Ratings
A common misunderstanding about processors is their different speed ratings. This section covers
processor speed in general, and then provides more specific information about Intel processors.
A computer system’s clock speed is measured as a frequency, usually expressed as a number of
cycles per second. A crystal oscillator controls clock speeds using a sliver of quartz sometimes
contained in what looks like a small tin container. Newer systems include the oscillator circuitry
in the motherboard chipset, so it might not be a visible separate component on newer boards. As
voltage is applied to the quartz, it begins to vibrate (oscillate) at a harmonic rate dictated by the
shape and size of the crystal (sliver). The oscillations emanate from the crystal in the form of a
current that alternates at the harmonic rate of the crystal. This alternating current is the clock
signal that forms the time base on which the computer operates. A typical computer system runs
millions of these cycles per second, so speed is measured in megahertz. (One hertz is equal to one
cycle per second.) An alternating current signal is like a sine wave, with the time between the
peaks of each wave defining the frequency (see Figure 3.1).
Clock Cycles
One cycle
Voltage
Figure 3.1
Time
Alternating current signal showing clock cycle timing.
Note
The hertz was named for the German physicist Heinrich Rudolf Hertz. In 1885, Hertz confirmed the electromagnetic theory, which states that light is a form of electromagnetic radiation and is propagated as waves.
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A single cycle is the smallest element of time for the processor. Every action requires at least one
cycle and usually multiple cycles. To transfer data to and from memory, for example, a modern
processor such as the Pentium II needs a minimum of three cycles to set up the first memory
transfer, and then only a single cycle per transfer for the next three to six consecutive transfers.
The extra cycles on the first transfer are normally called wait states. A wait state is a clock tick in
which nothing happens. This ensures that the processor isn’t getting ahead of the rest of the
computer.
◊◊ See “SIMMs and DIMMs,” p. 437.
The time required to execute instructions also varies:
■ 8086 and 8088. The original 8086 and 8088 processors take an average of 12 cycles to execute a single instruction.
■ 286 and 386. The 286 and 386 processors improve this rate to about 4.5 cycles per instruction.
■ 486. The 486 and most other fourth generation Intel compatible processors such as the
AMD 5x86 drop the rate further, to about two cycles per instruction.
■ Pentium. The Pentium architecture and other fifth generation Intel compatible processors
such as those from AMD and Cyrix include twin instruction pipelines and other improvements that provide for operation at one or two instructions per cycle.
■ Pentium Pro, Pentium II/III, Celeron and Xeon. These Intel P6 class processors, as well as other
sixth generation processors such as those from AMD and Cyrix, can execute as many as
three or more instructions per cycle.
Different instruction execution times (in cycles) make it difficult to compare systems based purely
on clock speed, or number of cycles per second. How can two processors that run at the same
clock rate perform differently with one running “faster” than the other? The answer is simple:
efficiency.
The main reason why the 486 was considered fast relative to a 386 is that it executes twice as
many instructions in the same number of cycles. The same thing is true for a Pentium; it executes about twice as many instructions in a given number of cycles as a 486. This means that
given the same clock speed, a Pentium will be twice as fast as a 486, and consequently a 133MHz
486 class processor (such as the AMD 5x86-133) is not even as fast as a 75MHz Pentium! That is
because Pentium megahertz are “worth” about double what 486 megahertz are worth in terms of
instructions completed per cycle. The Pentium II and III are about 50 percent faster than an
equivalent Pentium at a given clock speed because they can execute about that many more
instructions in the same number of cycles.
Comparing relative processor performance, you can see that a 600MHz Pentium III is about equal
to a (theoretical) 900MHz Pentium, which is about equal to an 1,800MHz 486, which is about
equal to a 3,600MHz 386 or 286, which is about equal to a 7,200MHz 8088. The original PCs’
8088 ran at only 4.77MHz; today, we have systems that are comparatively about 1,500 times
faster. As you can see, you have to be careful in comparing systems based on pure MHz alone,
because many other factors affect system performance.
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Evaluating CPU performance can be tricky. CPUs with different internal architectures do things
differently and may be relatively faster at certain things and slower at others. To fairly compare
different CPUs at different clock speeds, Intel has devised a specific series of benchmarks called
the iCOMP (Intel Comparative Microprocessor Performance) index that can be run against
processors to produce a relative gauge of performance. The iCOMP index benchmark has been
updated twice and released in original iCOMP, iCOMP 2.0, and now iCOMP 3.0 versions.
Table 3.3 shows the relative power, or iCOMP 2.0 index, for several processors.
Table 3.3
Intel iCOMP 2.0 Index Ratings
Processor
iCOMP
2.0 Index
Processor
iCOMP
2.0 Index
Pentium 75
67
Pentium Pro 200
220
Pentium 100
90
Celeron 300
226
Pentium 120
100
Pentium II 233
267
Pentium 133
111
Celeron 300A
296
Pentium 150
114
Pentium II 266
303
Pentium 166
127
Celeron 333
318
332
Pentium 200
142
Pentium II 300
Pentium-MMX 166
160
Pentium II Overdrive 300
351
Pentium Pro 150
168
Pentium II 333
366
Pentium-MMX 200
182
Pentium II 350
386
Pentium Pro 180
197
Pentium II Overdrive 333
387
Pentium-MMX 233
203
Pentium II 400
440
Celeron 266
213
Pentium II 450
483
The iCOMP 2.0 index is derived from several independent benchmarks and is a stable indication
of relative processor performance. The benchmarks balance integer with floating point and multimedia performance.
Recently Intel discontinued the iCOMP 2.0 index and released the iCOMP 3.0 index. iCOMP 3.0
is an updated benchmark that incorporates an increasing use of 3D, multimedia, and Internet
technology and software, as well as the increasing use of rich data streams and compute-intensive
applications, including 3D, multimedia, and Internet technology. iCOMP 3.0 combines six
benchmarks: WinTune 98 Advanced CPU Integer test, CPUmark 99, 3D WinBench 99-3D
Lighting and Transformation Test, MultimediaMark 99, Jmark 2.0 Processor Test, and WinBench
99-FPU WinMark. These newer benchmarks take advantage of the SSE (Streaming SIMD
Extensions), additional graphics and sound instructions built in to the PIII. Without taking
advantage of these new instructions, the PIII would benchmark at about the same speed as a PII
at the same clock rate.
The following table shows the iCOMP Index 3.0 ratings for newer Intel processors.
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Processor
iCOMP 3.0 Index
Pentium II 450MHz
1240
Pentium III 450MHz
1500
Pentium III 500MHz
1650
Pentium III 550MHz
1780
Chapter 3
45
Considerations When Interpreting iCOMP Scores
Each processor’s rating is calculated at the time the processor is introduced, using a particular, well-configured,
commercially available system. Relative iCOMP Index 3.0 scores and actual system performance might be
affected by future changes in software design and configuration. Relative scores and actual system performance
also may be affected by differences in components or characteristics of microprocessors such as L2 cache, bus
speed, extended multimedia or graphics instructions, or improvements in the microprocessor manufacturing process.
Differences in hardware components other than microprocessors used in the test systems also can affect how
iCOMP scores relate to actual system performance. iCOMP 3.0 ratings cannot be compared with earlier versions
of the iCOMP index because different benchmarks and weightings are used in calculating the result.
Processor Speeds and Markings Versus Motherboard
Speed
Another confusing factor when comparing processor performance is that virtually all modern
processors since the 486DX2 run at some multiple of the motherboard speed. For example, a
Celeron 466 runs at a multiple of seven times the motherboard speed of 66MHz, while a Pentium
III 550 runs at five and a half times the motherboard speed of 100MHz. Up until early 1998, most
motherboards ran at 66MHz or less because that is all Intel supported with their processors until
then. Starting in April 1998, Intel released both processors and motherboard chipsets designed to
run at 100MHz. Cyrix has a few processors designed to run on 75MHz motherboards, and many
Pentium motherboards are capable of running that speed as well, although technically Intel
never supported it. AMD also has versions of the K6-2 designed to run at motherboard speeds of
100MHz.
By late 1999, motherboards running at 133MHz should be available, which is the next step in
board speed.
Normally, you can set the motherboard speed and multiplier setting via jumpers or other configuration mechanism (such as CMOS setup) on the motherboard.
Modern systems use a variable-frequency synthesizer circuit usually found in the main motherboard chipset to control the motherboard and CPU speed. Most Pentium motherboards will have
three or four speed settings. The processors used today are available in a variety of versions that
run at different frequencies based on a given motherboard speed. For example, most of the
Pentium chips run at a speed that is some multiple of the true motherboard speed. For example,
Pentium processors and motherboards run at the speeds shown in Table 3.4.
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For information on specific AMD or Cyrix processors, see their respective sections later in this
chapter.
Table 3.4
Intel Processor and Motherboard Speeds
CPU Type
CPU Speed
(MHz)
Clock
Multiplier
Motherboard Speed
(MHz)
Pentium
60
1x
60
Pentium
66
1x
66
Pentium
75
1.5x
50
Pentium
90
1.5x
60
Pentium
100
1.5x
66
Pentium
120
2x
60
Pentium
133
2x
66
Pentium
150
2.5x
60
Pentium/Pentium Pro
166
2.5x
66
Pentium/Pentium Pro
180
3x
60
Pentium/Pentium Pro
200
3x
66
Pentium/Pentium II
233
3.5x
66
Pentium(Mobile)/Pentium-II/Celeron
266
4x
66
Pentium II/Celeron
300
4.5x
66
Pentium II/Celeron
333
5x
66
Pentium II/Celeron
366
5.5x
66
Pentium Celeron
400
6x
66
Pentium Celeron
433
6.5x
66
Pentium Celeron
466
7x
66
Pentium Celeron
500
7.5x
66
Pentium II
350
3.5x
100
Pentium II/Xeon
400
4x
100
Pentium II/III/Xeon
450
4.5x
100
Pentium III/Xeon
500
5x
100
Pentium III/Xeon
533
4x
133
Pentium III/Xeon
550
5.5x
100
Pentium III/Xeon
600
4.5x
133
If all other variables are equal—including the type of processor, the number of wait states (empty
cycles) added to different types of memory accesses, and the width of the data bus—you can
compare two systems by their respective clock rates. However, the construction and design of the
memory controller (contained in the motherboard chipset) as well as the type and amount of
memory installed can have an enormous effect on a system’s final execution speed.
In building a processor, a manufacturer tests it at different speeds, temperatures, and pressures.
After the processor is tested, it receives a stamp indicating the maximum safe speed at which the
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47
unit will operate under the wide variation of temperatures and pressures encountered in normal
operation. The rating system usually is simple. For example, the top of the processor in one of
my systems is marked like this:
A80486DX2–66
The A is Intel’s indicator that this chip has a Ceramic Pin Grid Array form factor, or an indication
of the physical packaging of the chip.
The 80486DX2 is the part number, which identifies this processor as a clock-doubled 486DX
processor.
The -66 at the end indicates that this chip is rated to run at a maximum speed of 66MHz.
Because of the clock doubling, the maximum motherboard speed is 33MHz. This chip would be
acceptable for any application in which the chip runs at 66MHz or slower. For example, you
could use this processor in a system with a 25MHz motherboard, in which case the processor
would happily run at 50MHz.
Most 486 motherboards also had a 40MHz setting, in which case the DX2 would run at 80MHz
internally. Because this is 14MHz beyond its rated speed, many would not work; or if it worked at
all, it would be only for a short time. On the other hand, I have found that most of the newer
chips marked with –66 ratings seem to run fine (albeit somewhat hotter) at the 40/80MHz settings. This is called overclocking and can end up being a simple, cost-effective way to speed up
your system. However, I would not recommend this for mission-critical applications where the
system reliability is of the utmost importance; a system pushed beyond specification like this can
often exhibit erratic behavior under stress.
Note
One good source of online overclocking information is located at http://www.sysopt.com. It includes, among
other things, fairly thorough overclocking FAQs and an ongoing survey of users who have successfully (and sometimes unsuccessfully) overclocked their CPUs. Note that many of the newer Intel processors incorporate fixed bus
multipliers, which effectively prevent or certainly reduce the ability to overclock. Unfortunately this can be overridden with a simple hardware fix, and many counterfeit processor vendors are selling remarked (overclocked) chips.
Sometimes, however, the markings don’t seem to indicate the speed directly. In the older 8086,
for example, -3 translates to 6MHz operation. This marking scheme is more common in some of
the older chips, which were manufactured before some of the marking standards used today were
standardized.
The Processor Heat Sink Might Hide the Rating
Most processors have heat sinks on top of them, which can prevent you from reading the rating printed on the
chip.
A heat sink is a metal device that draws heat away from an electronic device. Most processors running at 50MHz
and faster should have a heat sink installed to prevent the processor from overheating.
Fortunately, most CPU manufacturers are placing marks on the top and bottom of the processor. If the heat sink is
difficult to remove from the chip, you can take the heat sink and chip out of the socket together and read the markings on the bottom of the processor to determine what you have.
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Cyrix P-Ratings
Cyrix/IBM 6x86 processors use a PR (Performance Rating) scale that is not equal to the true clock
speed in megahertz. For example, the Cyrix 6x86MX/MII-PR366 actually runs at only 250MHz
(2.5 × 100MHz). This is a little misleading—you must set up the motherboard as if a 250MHz
processor were being installed, not the 366MHz you might suspect. Unfortunately this leads people to believe these systems are faster than they really are. Table 3.5 shows the relationship
between the Cyrix 6x86, 6x86MX, and M-II P-Ratings versus the actual chip speeds in MHz.
Table 3.5
Cyrix P-Ratings Versus Actual Chip Speeds in MHz
Cyrix CPU
Type
P-Rating
Actual CPU
Speed (MHz)
Clock
Multiplier
Motherboard
Speed (MHz)
6x86
6x86
6x86
6x86
6x86
6x86
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
6x86MX
M-II
M-II
M-II
M-II
PR90
PR120
PR133
PR150
PR166
PR200
PR133
PR133
PR150
PR150
PR166
PR166
PR166
PR166
PR200
PR200
PR200
PR200
PR233
PR233
PR233
PR266
PR266
PR266
PR300
PR300
PR333
PR366
80
100
110
120
133
150
100
110
120
125
133
137.5
150
150
150
165
166
180
166
187.5
200
207.5
225
233
225
233
250
250
2x
2x
2x
2x
2x
2x
2x
2x
2x
2.5x
2x
2.5x
3x
2.5x
2x
3x
2.5x
3x
2x
2.5x
3x
2.5x
3x
3.5x
3x
3.5x
3x
2.5x
40
50
55
60
66
75
50
55
60
50
66
55
50
60
75
55
66
60
83
75
66
83
75
66
75
66
83
100
Note that a given P-Rating can mean several different actual CPU speeds, for example a Cyrix
6x86MX-PR200 might actually be running at 150MHz, 165MHz, 166MHz, or 180MHz, but not at
200MHz.
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49
This P-Rating was supposed to indicate speed in relation to an Intel Pentium processor, but the
processor they are comparing to is the original non-MMX, small L1 cache version running on an
older motherboard platform with an older chipset and slower technology memory. The P-Rating
does not compare well against the Celeron, Pentium II, or Pentium III processors. In that case
these chips are more comparative at their true speed. In other words, the MII-PR366 really runs at
only 250MHz, and compares well against Intel processors running at closer to that speed. I consider calling a chip an MII-366 when it really runs at only 250MHz very misleading, to say the
least.
AMD P-Ratings
Although both AMD and Cyrix concocted this misleading P-Rating system, AMD thankfully only
used it for a short time and only on the older K5 processor. They still have the PR designation
stamped on their newer chips, but all K6 processors have PR numbers that match their actual
CPU speed in MHz. Table 3.6 shows the P-Rating and actual speeds of the AMD K5 and K6
processors.
Table 3.6
AMD P-Ratings Versus Actual Chip Speeds in MHz
Cyrix CPU
Type
P-Rating
Actual CPU
Speed (MHz)
Clock
Multiplier
Motherboard
Speed (MHz)
K5
K5
K5
K5
K5
K5
K6
K6
K6
K6
K6
K6-2
K6-2
K6-2
K6-2
K6-2
K6-2
K6-2
K6-2
K6-2
K6-2
K6-2
K6-2
K6-3
K6-3
PR75
PR90
PR100
PR120
PR133
PR166
PR166
PR200
PR233
PR266
PR300
PR233
PR266
PR300
PR300
PR333
PR333
PR350
PR366
PR380
PR400
PR450
PR475
PR400
PR450
75
90
100
90
100
116.7
166
200
233
266
300
233
266
300
300
333
333
350
366
380
400
450
475
400
450
1.5x
1.5x
1.5x
1.5x
1.5x
1.75x
2.5x
3x
3.5x
4x
4.5x
3.5x
4x
4.5x
3x
5x
3.5x
3.5x
5.5x
4x
4x
4.5x
5x
4x
4.5x
50
60
66
60
66
66
66
66
66
66
66
66
66
66
100
66
95
100
66
95
100
100
95
100
100
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Data Bus
Perhaps the most common ways to describe a processor is by the speed at which it runs and the
width of the processor’s external data bus. This defines the number of data bits that can be
moved into or out of the processor in one cycle. A bus is a series of connections that carry common signals. Imagine running a pair of wires from one end of a building to another. If you connect a 110v AC power generator to the two wires at any point and place outlets at convenient
locations along the wires, you have constructed a power bus. No matter which outlet you plug
the wires into, you have access to the same signal, which in this example is 110v AC power. Any
transmission medium that has more than one outlet at each end can be called a bus. A typical
computer system has several internal and external buses.
The processor bus discussed most often is the external data bus—the bundle of wires (or pins)
used to send and receive data. The more signals that can be sent at the same time, the more data
can be transmitted in a specified interval and, therefore, the faster (and wider) the bus. A wider
data bus is like having a highway with more lanes, which allows for greater throughput.
Data in a computer is sent as digital information consisting of a time interval in which a single
wire carries 5v to signal a 1 data bit, or 0v to signal a 0 data bit. The more wires you have, the
more individual bits you can send in the same time interval. A chip such as the 286 or 386SX,
which has 16 wires for transmitting and receiving such data, has a 16-bit data bus. A 32-bit chip,
such as the 386DX and 486, has twice as many wires dedicated to simultaneous data transmission
as a 16-bit chip; a 32-bit chip can send twice as much information in the same time interval as a
16-bit chip. Modern processors such as the Pentium series have 64-bit external data buses. This
means that Pentium processors including the original Pentium, Pentium Pro, and Pentium II can
all transfer 64 bits of data at a time to and from the system memory.
A good way to understand this flow of information is to consider a highway and the traffic it carries. If a highway has only one lane for each direction of travel, only one car at a time can move
in a certain direction. If you want to increase traffic flow, you can add another lane so that twice
as many cars pass in a specified time. You can think of an 8-bit chip as being a single-lane highway because one byte flows through at a time. (One byte equals eight individual bits.) The 16-bit
chip, with two bytes flowing at a time, resembles a two-lane highway. You may have four lanes in
each direction to move a large number of automobiles; this structure corresponds to a 32-bit data
bus, which has the capability to move four bytes of information at a time. Taking this further, a
64-bit data bus is like having an 8-lane highway moving data in and out of the chip!
Just as you can describe a highway by its lane width, you can describe a chip by the width of its
data bus. When you read an advertisement that describes a 32-bit or 64-bit computer system, the
ad usually refers to the CPU’s data bus. This number provides a rough idea of the chip’s performance potential (and, therefore, the system).
Perhaps the most important ramification of the data bus in a chip is that the width of the data
bus also defines the size of a bank of memory. This means that a 32-bit processor, such as the 486
class chips, reads and writes memory 32 bits at a time. Pentium class processors, including the
Pentium II, read and write memory 64 bits at a time. Because standard 72-pin SIMMs (Single
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Inline Memory Modules) are only 32 bits wide, they must be installed one at a time in most 486
class systems; they’re installed two at a time in most Pentium class systems. Newer DIMMs (Dual
Inline Memory Modules) are 64 bits wide, so they are installed one at a time in Pentium class systems. Each DIMM is equal to a complete bank of memory in Pentium systems, which makes system configuration easy, because they can then be installed or removed one at a time.
◊◊ See “Memory Banks,” p. 451.
Internal Registers (Internal Data Bus)
The size of the internal registers indicate how much information the processor can operate on at
one time and how it moves data around internally within the chip. This is sometimes also
referred to as the internal data bus. The register size is essentially the same as the internal data
bus size. A register is a holding cell within the processor; for example, the processor can add
numbers in two different registers, storing the result in a third register. The register size determines the size of data the processor can operate on. The register size also describes the type of
software or commands and instructions a chip can run. That is, processors with 32-bit internal
registers can run 32-bit instructions that are processing 32-bit chunks of data, but processors with
16-bit registers cannot. Most advanced processors today—chips from the 386 to the Pentium II—
use 32-bit internal registers and can therefore run the same 32-bit operating systems and software.
Some processors have an internal data bus (made up of data paths and storage units called registers) that is larger than the external data bus. The 8088 and 386SX are examples of this structure.
Each chip has an internal data bus twice the width of the external bus. These designs, which
sometimes are called hybrid designs, usually are low-cost versions of a “pure” chip. The 386SX,
for example, can pass data around internally with a full 32-bit register size; for communications
with the outside world, however, the chip is restricted to a 16-bit–wide data path. This design
enables a systems designer to build a lower-cost motherboard with a 16-bit bus design and still
maintain software and instruction set compatibility with the full 32-bit 386.
Internal registers often are larger than the data bus, which means that the chip requires two
cycles to fill a register before the register can be operated on. For example, both the 386SX and
386DX have internal 32-bit registers, but the 386SX has to “inhale” twice (figuratively) to fill
them, whereas the 386DX can do the job in one “breath.” The same thing would happen when
the data is passed from the registers back out to the system bus.
The Pentium is an example of this type of design. All Pentiums have a 64-bit data bus and 32-bit
registers—a structure that might seem to be a problem until you understand that the Pentium has
two internal 32-bit pipelines for processing information. In many ways, the Pentium is like two
32-bit chips in one. The 64-bit data bus provides for very efficient filling of these multiple registers. Multiple pipelines are called superscalar architecture, which was introduced with the Pentium
processor.
◊◊ See “Pentium Processors,” p.129.
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More advanced sixth-generation processors such as the Pentium Pro and Pentium II/III have as
many as six internal pipelines for executing instructions. Although some of these internal pipes
are dedicated to special functions, these processors can still execute as many as three instructions
in one clock cycle.
Address Bus
The address bus is the set of wires that carry the addressing information used to describe the
memory location to which the data is being sent or from which the data is being retrieved. As
with the data bus, each wire in an address bus carries a single bit of information. This single bit is
a single digit in the address. The more wires (digits) used in calculating these addresses, the
greater the total number of address locations. The size (or width) of the address bus indicates the
maximum amount of RAM that a chip can address.
The highway analogy can be used to show how the address bus fits in. If the data bus is the highway and the size of the data bus is equivalent to the number of lanes, the address bus relates to
the house number or street address. The size of the address bus is equivalent to the number of
digits in the house address number. For example, if you live on a street in which the address is
limited to a two-digit (base 10) number, no more than 100 distinct addresses (00–99) can exist for
that street (10 to the power of 2). Add another digit, and the number of available addresses
increases to 1,000 (000–999), or 10 to the power of 3.
Computers use the binary (base 2) numbering system, so a two-digit number provides only four
unique addresses (00, 01, 10, and 11) calculated as 2 to the power of 2. A three-digit number provides only eight addresses (000–111), which is 2 to the third power. For example, the 8086 and
8088 processors use a 20-bit address bus that calculates as a maximum of 2 to the 20th power or
1,048,576 bytes (1MB) of address locations. Table 3.7 describes the memory-addressing capabilities of Intel processors.
Table 3.7 Intel and Intel Compatible Processor Memory-Addressing
Capabilities
Processor Family
Address Bus
Bytes
KB
MB
GB
8088/8086
20-bit
1,048,576
1,024
1
—
286/386SX
24-bit
16,777,216
16,384
16
—
386DX/486/P5 Class
32-bit
4,294,967,296
4,194,304
4,096
4
P6 Class
36-bit
68,719,476,736
67,108,864
65,536
64
The data bus and address bus are independent, and chip designers can use whatever size they
want for each. Usually, however, chips with larger data buses have larger address buses. The sizes
of the buses can provide important information about a chip’s relative power, measured in two
important ways. The size of the data bus is an indication of the chip’s information-moving capability, and the size of the address bus tells you how much memory the chip can handle.
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Internal Level 1 (L1) Cache
All modern processors starting with the 486 family include an integrated (L1) cache and controller. The integrated L1 cache size varies from processor to processor, starting at 8KB for the
original 486DX and now up to 32KB, 64KB, or more in the latest processors.
Since L1 cache is always built in to the processor die, it runs at the full core speed of the processor
internally. By full core speed, I mean this cache runs at the higher clock multiplied internal
processor speed rather than the external motherboard speed. This cache basically is an area of
very fast memory built in to the processor and is used to hold some of the current working set of
code and data. Cache memory can be accessed with no wait states because it is running at the
same speed as the processor core.
Using cache memory reduces a traditional system bottleneck because system RAM often is much
slower than the CPU. This prevents the processor from having to wait for code and data from
much slower main memory therefore improving performance. Without the L1 cache, a processor
frequently would be forced to wait until system memory caught up.
L1 cache is even more important in modern processors because it is often the only memory in
the entire system that can truly keep up with the chip. Most modern processors are clock multiplied, which means they are running at a speed that is really a multiple of the motherboard they
are plugged into. The Pentium II 333MHz, for example, runs at a very high multiple of five times
the true motherboard speed of 66MHz. Because the main memory is plugged in to the motherboard, it can also run at only 66MHz maximum. The only 333MHz memory in such a system is
the L1 cache built into the processor core. In this example, the Pentium II 333MHz processor has
32KB of integrated L1 cache in two separate 16KB blocks.
◊◊ See “Memory Speeds,” p. 424.
If the data that the processor wants is already in the internal cache, the CPU does not have to
wait. If the data is not in the cache, the CPU must fetch it from the Level 2 cache or (in less
sophisticated system designs) from the system bus, meaning main memory directly.
In order to understand the importance of cache, you need to know the relative speeds of processors and memory. The problem with this is that processor speed is normally expressed in MHz
(millions of cycles per second), while memory speeds are often expressed in nanoseconds (billionths of a second per cycle).
Both are really time or frequency based measurements, and a chart comparing them can be found
in Chapter 6, “Memory,” Table 6.3. In this table you will note that a 200MHz processor equates
to five nanosecond cycling, which means you would need 5ns memory to keep pace with a
200MHz CPU. Also note that the motherboard of a 200MHz system will normally run at 66MHz,
which corresponds to a speed of 15ns per cycle, and require 15ns memory to keep pace. Finally
note that 60ns main memory (common on many Pentium class systems) equates to a clock speed
of approximately 16MHz. So in a typical Pentium 200 system, you have a processor running at
200MHz (5ns per cycle), a motherboard running at 66MHz (15ns per cycle), and main memory
running at 16MHz (60ns per cycle).
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To learn how the L1 and L2 cache work, consider the following analogy.
This story involves a person (in this case you) eating food to act as the processor requesting and
operating on data from memory. The kitchen where the food is prepared is the main memory
(SIMM/DIMM) RAM. The cache controller is the waiter, and the L1 cache is the table you are
seated at. L2 cache will be introduced as a food cart, which is positioned between your table and
the kitchen.
Okay, here’s the story. Say you start to eat at a particular restaurant every day at the same time.
You come in, sit down, and order a hot dog. To keep this story proportionately accurate, let’s say
you normally eat at the rate of one bite (byte? <g>) every five seconds (200MHz = 5ns cycling). It
also takes 60 seconds for the kitchen to produce any given item that you order (60ns main
memory).
So, when you first arrive, you sit down, order a hot dog, and you have to wait for 60 seconds for
the food to be produced before you can begin eating. Once the waiter brings the food, you start
eating at your normal rate. Pretty quickly you finish the hot dog, so you call the waiter and order
a hamburger. Again you wait 60 seconds while the hamburger is being produced. When it arrives
again you begin eating at full speed. After you finish the hamburger, you order a plate of fries.
Again you wait, and after it is delivered 60 seconds later you eat it at full speed. Finally, you
decide to finish the meal and order cheesecake for dessert. After another 60-second wait, you can
again eat dessert at full speed. Your overall eating experience consists of mostly a lot of waiting,
followed by short bursts of actual eating at full speed.
After coming into the restaurant for two consecutive nights at exactly 6 p.m. and ordering the
same items in the same order each time, on the third night the waiter begins to think; “I know
this guy is going to be here at 6 p.m., order a hot dog, a hamburger, fries, and then cheesecake.
Why don’t I have these items prepared in advance and surprise him, maybe I’ll get a big tip.” So
you enter the restaurant, order a hot dog, and the waiter immediately puts it on your plate, with
no waiting! You then proceed to finish the hot dog and right as you were about to request the
hamburger, the waiter deposits one on your plate. The rest of the meal continues in the same
fashion, and you eat the entire meal, taking a bite every five seconds, and never have to wait for
the kitchen to prepare the food. Your overall eating experience this time consists of all eating,
with no waiting for the food to be prepared, due primarily to the intelligence and thoughtfulness
of your waiter.
This analogy exactly describes the function of the L1 cache in the processor. The L1 cache itself is
the table that can contain one or more plates of food. Without a waiter, the space on the table is
a simple food buffer. When stocked, you can eat until the buffer is empty, but nobody seems to
be intelligently refilling it. The waiter is the cache controller who takes action and adds the intelligence to decide what dishes are to be placed on the table in advance of your needing them. Like
the real cache controller, he uses his skills to literally guess what food you will require next, and
if and when he guesses right, you never have to wait.
Let’s now say on the fourth night you arrive exactly on time and start off with the usual hot dog.
The waiter, by now really feeling confident, has the hot dog already prepared when you arrive, so
there is no waiting.
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Just as you finish the hot dog, and right as he is placing a hamburger on your plate, you say
“Gee, I’d really like a bratwurst now; I didn’t actually order this hamburger.” The waiter guessed
wrong, and the consequence is that this time you have to wait the full 60 seconds as the kitchen
prepares your brat. This is known as a cache miss, where the cache controller did not correctly fill
the cache with the data the processor actually needed next. The result is waiting, or in the case of
a sample 200MHz Pentium system, the system essentially throttles back to 16MHz (RAM speed)
whenever there is a cache miss. According to Intel, the L1 cache in most of their processors has
approximately a 90 percent hit ratio. This means that the cache has the correct data 90 percent of
the time and consequently the processor runs at full speed, 200MHz in this example, 90 percent
of the time. However, 10 percent of the time the cache controller guesses wrong and the data has
to be retrieved out of the significantly slower main memory, meaning the processor has to wait.
This essentially throttles the system back to RAM speed, which in this example was 60ns or
16MHz.
Level 2 (L2) Cache
To mitigate the dramatic slowdown every time there is a cache miss, a secondary or L2 cache can
be employed.
Using the restaurant analogy I used to explain L1 cache in the previous section, I’ll equate the L2
cache to a cart of additional food items placed strategically such that the waiter can retrieve food
from it in 15 seconds. In an actual Pentium class system, the L2 cache is mounted on the motherboard, which means it runs at motherboard speed—66MHz or 15ns in this example. Now if you
ask for an item the waiter did not bring in advance to your table, instead of making the long trek
back to the kitchen to retrieve the food and bring it back to you 60 seconds later, he can first
check the cart where he has placed additional items. If the requested item is there, he will return
with it in only 15 seconds. The net effect in the real system is that instead of slowing down from
200MHz to 16MHz waiting for the data to come from the 60ns main memory, the data can
instead be retrieved from the 15ns (66MHz) L2 cache instead. The effect is that the system slows
down from 200MHz to 66MHz.
Most L2 caches have a hit ratio also in the 90 percent range, which means that if you look at the
system as a whole, 90 percent of the time it will be running at full speed (200MHz in this example) by retrieving data out of the L1 cache. Ten percent of the time it will slow down to retrieve
the data from the L2 cache. Ninety percent of that time the data will be in the L2, and 10 percent
of that time you will have to go to the slow main memory to get the data due to an L2 cache
miss. This means that our sample system runs at full processor speed 90 percent of the time
77(200MHz in this case), motherboard speed 9 percent of the time (66MHz in this case), and
RAM speed about 1 percent of the time (16MHz in this case). You can clearly see the importance
of both the L1 and L2 caches; without them the system will be using main memory more often,
which is significantly slower than the processor.
In Pentium (P5) class systems, the L2 cache is normally found on the motherboard and must
therefore run at motherboard speed. Intel made a dramatic improvement to this in the P6 class
systems by migrating the L2 cache from the motherboard directly into the processor. In the Xeon
and Celeron processors, the L2 cache runs at full processor core speed, which means there is no
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waiting or slowing down after an L1 cache miss. In the mainstream Pentium II processors, for
economy reasons, the L2 cache runs at half the core processor speed, which is still significantly
faster than the motherboard.
Cache Organization
The organization of the cache memory in the 486 and Pentium family is called a four-way set
associative cache, which means that the cache memory is split into four blocks. Each block also is
organized as 128 or 256 lines of 16 bytes each.
To understand how a four-way set associative cache works, consider a simple example. In the simplest cache design, the cache is set up as a single block into which you can load the contents of a
corresponding block of main memory. This procedure is similar to using a bookmark to locate the
current page of a book that you are reading. If main memory equates to all the pages in the book,
the bookmark indicates which pages are held in cache memory. This procedure works if the
required data is located within the pages marked with the bookmark, but it does not work if you
need to refer to a previously read page. In that case, the bookmark is of no use.
An alternative approach is to maintain multiple bookmarks to mark several parts of the book
simultaneously. Additional hardware overhead is associated with having multiple bookmarks, and
you also have to take time to check all the bookmarks to see which one marks the pages of data
you need. Each additional bookmark adds to the overhead, but also increases your chance of
finding the desired pages.
If you settle on marking four areas in the book, you have essentially constructed a four-way set
associative cache. This technique splits the available cache memory into four blocks, each of
which stores different lines of main memory. Multitasking environments, such as Windows, are
good examples of environments in which the processor needs to operate on different areas of
memory simultaneously and in which a four-way cache would improve performance greatly.
The contents of the cache must always be in sync with the contents of main memory to ensure
that the processor is working with current data. For this reason, the internal cache in the 486
family is a write-through cache. Write-through means that when the processor writes information
out to the cache, that information is automatically written through to main memory as well.
By comparison, the Pentium and later chips have an internal write-back cache, which means that
both reads and writes are cached, further improving performance. Even though the internal 486
cache is write-through, the system can employ an external write-back cache for increased performance. In addition, the 486 can buffer up to four bytes before actually storing the data in RAM,
improving efficiency in case the memory bus is busy.
Another feature of improved cache designs is that they are non-blocking. This is a technique for
reducing or hiding memory delays by exploiting the overlap of processor operations with data
accesses. A non-blocking cache allows program execution to proceed concurrently with cache
misses as long as certain dependency constraints are observed. In other words, the cache can handle a cache miss much better and allow the processor to continue doing something
non-dependent on the missing data.
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Chapter 3
The cache controller built into the processor also is responsible for watching the memory bus
when alternative processors, known as busmasters, are in control of the system. This process of
watching the bus is referred to as bus snooping. If a busmaster device writes to an area of memory
that also is stored in the processor cache currently, the cache contents and memory no longer
agree. The cache controller then marks this data as invalid and reloads the cache during the next
memory access, preserving the integrity of the system.
A secondary external L2 cache of extremely fast static RAM (SRAM) chips also is used in most 486
and Pentium-based systems. It further reduces the amount of time that the CPU must spend waiting for data from system memory. The function of the secondary processor cache is similar to
that of the onboard cache. The secondary processor cache holds information that is moving to
the CPU, thereby reducing the time that the CPU spends waiting and increasing the time that
the CPU spends performing calculations. Fetching information from the secondary processor
cache rather than from system memory is much faster because of the SRAM chips’ extremely fast
speed—15 nanoseconds (ns) or less.
Pentium systems incorporate the secondary cache on the motherboard, while Pentium Pro and
Pentium II systems have the secondary cache inside the processor package. By moving the L2
cache into the processor, systems are capable of running at speeds higher than the motherboard—up to as fast as the processor core.
As clock speeds increase, cycle time decreases. Most SIMM memory used in Pentium and earlier
systems was 60ns, which works out to be only about 16MHz! Standard motherboard speeds are
now 66MHz, 100MHz, or 133MHz, and processors are available at 600MHz or more. Newer systems don’t use cache on the motherboard any longer, as the faster SDRAM or RDRAM used in
modern Pentium Celeron/II/III systems can keep up with the motherboard speed. The trend
today is toward integrating the L2 cache into the processor die just like the L1 cache. This allows
the L2 to run at full core speed because it is now a part of the core. Cache speed is always more
important than size. The rule is that a smaller but faster cache is always better than a slower but
bigger cache. Table 3.8 illustrates the need for and function of L1 (internal) and L2 (external)
caches in modern systems.
Table 3.8
CPU Speeds Relative to Cache, SIMM/DIMM, and Motherboard
CPU Type:
Pentium
Pentium Pro
Pentium II 333
CPU speed:
233MHz
200MHz
333MHz
L1 cache speed:
4ns (233MHz)
5ns (200MHz)
3ns (333MHz)
L2 cache speed:
15ns (66MHz)
5ns (200MHz)
6ns (167MHz)
Motherboard speed:
66MHz
66MHz
66MHz
SIMM/DIMM speed:
60ns (16MHz)
60ns (16MHz)
15ns (66MHz)
SIMM/DIMM type:
FPM/EDO
FPM/EDO
SDRAM
(continues)
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Continued
CPU Type:
Celeron 500
Pentium III 500
Pentium III 600
CPU speed:
500 Hz
500MHz
600MHz
L1 cache speed:
2ns (500MHz)
2ns (500 Hz)
1.7ns (600MHz)
L2 cache speed:
2ns (500MHz)
4ns (250MHz)
1.7ns (600MHz)
Motherboard speed:
66MHz
100MHz
133MHz
SIMM/DIMM speed:
15ns (66MHz)
10ns (100MHz)
7.5ns (133MHz)
SIMM/DIMM type:
SDRAM
SDRAM
SDRAM/RDRAM
As you can see, having two levels of cache between the very fast CPU and the much slower main
memory helps minimize any wait states the processor might have to endure. This allows the
processor to keep working closer to its true speed.
Processor Modes
All Intel 32-bit and later processors, from the 386 on up, can run in several modes. Processor
modes refer to the various operating environments and affect the instructions and capabilities of
the chip. The processor mode controls how the processor sees and manages the system memory
and the tasks that use it.
Three different modes of operation possible are
■ Real mode (16-bit software)
■ Protected mode (32-bit software)
■ Virtual Real mode (16-bit programs within a 32-bit environment)
Real Mode
The original IBM PC included an 8088 processor that could execute 16-bit instructions using 16bit internal registers, and could address only 1MB of memory using 20 address lines. All original
PC software was created to work with this chip and was designed around the 16-bit instruction
set and 1MB memory model. For example, DOS and all DOS software, Windows 1.x through 3.x,
and all Windows 1.x through 3.x applications are written using 16-bit instructions. These 16-bit
operating systems and applications are designed to run on an original 8088 processor.
√√ See “Internal Registers,” p. 51.
√√ See “Address Bus,” p. 52.
Later processors such as the 286 could also run the same 16-bit instructions as the original 8088,
but much faster. In other words, the 286 was fully compatible with the original 8088 and could
run all 16-bit software just the same as an 8088, but, of course, that software would run faster.
The 16-bit instruction mode of the 8088 and 286 processors has become known as real mode. All
software running in real mode must use only 16-bit instructions and live within the 20-bit (1MB)
memory architecture it supports. Software of this type is normally single-tasking, which means
that only one program can run at a time. There is no built-in protection to keep one program
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from overwriting another program or even the operating system in memory, which means that if
more than one program is running, it is possible for one of them to bring the entire system to a
crashing halt.
Protected (32-bit) Mode
Then came the 386, which was the PC industry’s first 32-bit processor. This chip could run an
entirely new 32-bit instruction set. To take full advantage of the 32-bit instruction set you needed
a 32-bit operating system and a 32-bit application. This new 32-bit mode was referred to as protected mode, which alludes to the fact that software programs running in that mode are protected from overwriting one another in memory. Such protection helps make the system much
more crash-proof, as an errant program cannot very easily damage other programs or the operating system. In addition, a crashed program can be terminated, while the rest of the system continues to run unaffected.
Knowing that new operating systems and applications—which take advantage of the 32-bit protected mode—would take some time to develop, Intel wisely built in a backward compatible real
mode into the 386. That allowed it to run unmodified 16-bit operating systems and applications.
It ran them quite well—much faster than any previous chip. For most people, that was enough;
they did not necessarily want any new 32-bit software—they just wanted their existing 16-bit
software to run faster. Unfortunately, that meant the chip was never running in the 32-bit protected mode, and all the features of that capability were being ignored.
When a high-powered processor such as a Pentium III is running DOS (real mode), it acts like a
“Turbo 8088.” Turbo 8088 means that the processor has the advantage of speed in running any
16-bit programs; it otherwise can use only the 16-bit instructions and access memory within the
same 1MB memory map of the original 8088. This means if you have a 128MB Pentium III system running Windows 3.x or DOS, you are effectively using only the first megabyte of memory,
leaving the other 127MB largely unused!
New operating systems and applications that ran in the 32-bit protected mode of the modern
processors were needed. Being stubborn, we resisted all the initial attempts at getting switched
over to a 32-bit environment. It seems that as a user community, we are very resistant to change
and would be content with our older software running faster rather than adopting new software
with new features. I’ll be the first one to admit that I was one of those stubborn users myself!
Because of this resistance, 32-bit operating systems such as UNIX or variants such as Linux, OS/2,
and even Windows NT and Windows 2000 have had a very hard time getting any mainstream
share in the PC marketplace. Out of those, Windows 2000 is the only one that will likely become
a true mainstream product, and that is mainly because Microsoft has coerced us in that direction
with Windows 95 and 98. Windows 3.x was the last full 16-bit operating system. In fact, it was
not a complete operating system because it ran on top of DOS.
Microsoft realized how stubborn the installed base of PC users was so it developed Windows 95 as
a bridge to a full 32-bit world. Windows 95 is a mostly 32-bit operating system, but it retains
enough 16-bit capability to fully run our old 16-bit applications. Windows 95 came out in August
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1995, a full 10 years later than the introduction of the first 32-bit PC processor! It has taken us
only 10 years to migrate to software that can fully use the processors we have in front of us.
Virtual Real Mode
The key to the backward compatibility of the Windows 95 32-bit environment is the third mode
in the processor: virtual real mode. Virtual real is essentially a virtual real mode 16-bit environment that runs inside 32-bit protected mode. When you run a DOS prompt window inside
Windows 95/98, you have created a virtual real mode session. Because protected mode allows true
multitasking, you can actually have several real mode sessions running, each with its own software running on a virtual PC. This can all run simultaneously, even while other 32-bit applications are running.
Note that any program running in a virtual real mode window can access up to only 1MB of
memory, which that program will believe is the first and only megabyte of memory in the system. In other words, if you run a DOS application in a virtual real window, it will have a 640KB
limitation on memory usage. That is because there is only 1MB of total RAM in a 16-bit environment, and the upper 384KB is reserved for system use. The virtual real window fully emulates an
8088 environment, so that aside from speed, the software runs as if it were on an original real
mode-only PC. Each virtual machine gets its own 1MB address space, an image of the real hardware BIOS routines, and emulation of all other registers and features found in real mode.
Virtual real mode is used when you use a DOS window or run a DOS or Windows 3.x 16-bit program in Windows 95/98. When you start a DOS application, Windows 95 creates a virtual DOS
machine under which it can run.
One interesting thing to note is that all Intel (and Intel compatible—such as AMD and Cyrix)
processors power up in real mode. If you load a 32-bit operating system, it will automatically
switch the processor into 32-bit mode and take control from there.
Some DOS and Windows 3.x applications misbehave, which means they do things that even virtual real mode will not support. Diagnostics software is a perfect example of this. Such software
will not run properly in a real mode (virtual real) window under Windows 95/98 or NT, and
Windows 2000. In that case, you can still run your Pentium II in the original no-frills real mode
by interrupting the boot process and commanding the system to boot plain DOS. This is accomplished on most Windows 95/98/NT systems by pressing the F8 key when you see the prompt
Starting Windows... on the screen. You will then see the Startup menu; you can select one of
the command prompt choices, which tell the system to boot plain 16-bit real mode DOS. The
choice of Safe Mode Command Prompt is best if you are going to run true hardware diagnostics,
which do not normally run in protected mode and should be run with a minimum of drivers and
other software loaded.
Although real mode is used by DOS and “standard” DOS applications, there are special programs
available that “extend” DOS and allow access to extended memory (over 1MB). These are sometimes called DOS extenders and are usually included as a part of any DOS or Windows 3.x software that uses them. The protocol that describes how to make DOS work in protected mode is
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called DPMI (DOS protected mode interface). DPMI was used by Windows 3.x to access extended
memory for use with Windows 3.x applications. It allowed them to use more memory even
though they were still 16-bit programs. DOS extenders are especially popular in DOS games,
because they allow them to access much more of the system memory than the standard 1MB
most real mode programs can address. These DOS extenders work by switching the processor in
and out of real mode, or in the case of those that run under Windows, they use the DPMI interface built in to Windows, allowing them to share a portion of the system’s extended memory.
Another exception in real mode is that the first 64KB of extended memory is actually accessible
to the PC in real mode, despite the fact that it’s not supposed to be possible. This is the result of a
bug in the original IBM AT with respect to the 21st memory address line, known as A20 (A0 is
the first address line). By manipulating the A20 line, real mode software can gain access to the
first 64KB of extended memory—the first 64KB of memory past the first megabyte. This area of
memory is called the high memory area (HMA).
SMM (Power Management)
Spurred on primarily by the goal of putting faster and more powerful processors in laptop computers, Intel has created power management circuitry. This circuitry enables processors to conserve energy use and lengthen battery life. This was introduced initially in the Intel 486SL
processor, which is an enhanced version of the 486DX processor. Subsequently, the
power-management features were universalized and incorporated into all Pentium and later
processors. This feature set is called SMM, which stands for System Management Mode.
SMM circuitry is integrated into the physical chip but operates independently to control the
processor’s power use based on its activity level. It allows the user to specify time intervals after
which the CPU will be partially or fully powered down. It also supports the suspend/resume feature that allows for instant power on and power off, used mostly with laptop PCs. These settings
are normally controlled via system BIOS settings.
Superscalar Execution
The fifth-generation Pentium and newer processors feature multiple internal instruction execution pipelines, which enable them to execute multiple instructions at the same time. The 486
and all preceding chips can perform only a single instruction at a time. Intel calls the capability
to execute more than one instruction at a time superscalar technology. This technology provides
additional performance compared with the 486.
◊◊ See “Pentium Processor,” p. 129.
Superscalar architecture usually is associated with high-output RISC (Reduced Instruction Set
Computer) chips. An RISC chip has a less complicated instruction set with fewer and simpler
instructions. Although each instruction accomplishes less, overall the clock speed can be higher,
which can usually increase performance. The Pentium is one of the first CISC (Complex
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Instruction Set Computer) chips to be considered superscalar. A CISC chip uses a more rich, fullfeatured instruction set, which has more complicated instructions. As an example, say you
wanted to instruct a robot to screw in a light bulb. Using CISC instructions you would say
1. Pick up the bulb.
2. Insert it into the socket.
3. Rotate clockwise until tight.
Using RISC instructions you would say something more along the lines of
1. Lower hand.
2. Grasp bulb.
3. Raise hand.
4. Insert bulb into socket.
5. Rotate clockwise one turn.
6. Is bulb tight? If not repeat step 5.
7. End.
Overall many more RISC instructions are required to do the job because each instruction is simpler and does less. The advantage is that there are fewer overall commands the robot (or processor) has to deal with, and it can execute the individual commands more quickly, and thus in
many cases execute the complete task (or program) more quickly as well. The debate goes on
whether RISC or CISC is really better, but in reality there is no such thing as a pure RISC or CISC
chip.
Intel and compatible processors have generally been regarded as CISC chips, although the fifth
and sixth generation versions have many RISC attributes, and internally break CISC instructions
down into RISC versions.
MMX Technology
MMX technology is named for multi-media extensions, or matrix math extensions, depending on
whom you ask. Intel states that it is actually not an acronym and stands for nothing special;
however, the internal origins are probably one of the preceding. MMX technology was introduced in the later fifth-generation Pentium processors (see Figure 3.2) as a kind of add-on that
improves video compression/decompression, image manipulation, encryption, and I/O processing—all of which are used in a variety of today’s software.
MMX consists of two main processor architectural improvements. The first is very basic; all MMX
chips have a larger internal L1 cache than their non-MMX counterparts. This improves the performance of any and all software running on the chip, regardless of whether it actually uses the
MMX-specific instructions.
The other part of MMX is that it extends the processor instructions set with 57 new commands
or instructions, as well as a new instruction capability called Single Instruction, Multiple Data
(SIMD).
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Figure 3.2 An Intel Pentium MMX chip shown from the top and bottom (exposing the die).
Photograph used by permission of Intel Corporation.
Modern multimedia and communication applications often use repetitive loops that, while occupying 10 percent or less of the overall application code, can account for up to 90 percent of the
execution time. SIMD enables one instruction to perform the same function on multiple pieces of
data, similar to a teacher telling an entire class to “sit down,” rather than addressing each student
one at a time. SIMD allows the chip to reduce processor-intensive loops common with video,
audio, graphics, and animation.
Intel also added 57 new instructions specifically designed to manipulate and process video,
audio, and graphical data more efficiently. These instructions are oriented to the highly parallel
and often repetitive sequences often found in multimedia operations. Highly parallel refers to the
fact that the same processing is done on many different data points, such as when modifying a
graphic image.
Intel licensed the MMX capabilities to competitors such as AMD and Cyrix, who were then able
to upgrade their own Intel-compatible processors with MMX technology.
SSE (Streaming SIMD Extensions)
The Pentium III processor introduced in February 1999 included an update to MMX called
Streaming SIMD Extensions (SSE). SSE includes 70 new instructions for graphics and sound processing over what MMX provided. SSE is similar to MMX, in fact, it was originally called MMX-2
before it was released. Besides adding more MMX style instructions, the SSE instructions allow for
floating-point calculations, and now use a separate unit within the processor instead of sharing
the standard floating-point unit as MMX did.
The Streaming SIMD Extensions consist of 70 new instructions, including Single Instruction
Multiple Data (SIMD) floating-point, additional SIMD integer, and cacheability control instructions. Some of the technologies that benefit from the Streaming SIMD Extensions include
advanced imaging, 3D, streaming audio and video (DVD playback), and speech recognition applications. The benefits of SSE include the following:
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■ Higher resolution and higher quality image viewing and manipulation
■ High quality audio, MPEG2 video, and simultaneous MPEG2 encoding and decoding
■ Reduced CPU utilization for speech recognition, as well as higher accuracy and faster
response times
The SSE instructions are particularly useful with MPEG2 decoding, which is the standard scheme
used on DVD video discs. This means that SSE equipped processors should be capable of doing
MPEG2 decoding in software at full speed without requiring an additional hardware MPEG2
decoder card. SSE-equipped processors are much better and faster than previous processors when
it comes to speech recognition.
Note that for any of the SSE instructions to be beneficial, they must be encoded in the software,
which means that SSE-aware applications must be used to see the benefits. Most software companies writing graphics and sound-related software have updated those applications to be SSE-aware
and utilize the features of SSE. The processors, which include SSE, will also include MMX, so standard MMX-enabled applications will still run as they did on processors without SSE.
Dynamic Execution
First used in the P6 or sixth-generation processors, dynamic execution is an innovative combination of three processing techniques designed to help the processor manipulate data more efficiently. Those techniques are multiple branch prediction, data flow analysis, and speculative
execution. Dynamic execution enables the processor to be more efficient by manipulating data in
a more logically ordered fashion rather than simply processing a list of instructions, and it is one
of the hallmarks of all sixth-generation processors.
The way software is written can dramatically influence a processor’s performance. For example,
performance will be adversely affected if the processor is frequently required to stop what it is
doing and jump or branch to a point elsewhere in the program. Delays also occur when the
processor cannot process a new instruction until the current instruction is completed. Dynamic
execution allows the processor to not only dynamically predict the order of instructions, but execute them out of order internally, if necessary, for an improvement in speed.
Multiple Branch Prediction
Multiple branch prediction predicts the flow of the program through several branches. Using a
special algorithm, the processor can anticipate jumps or branches in the instruction flow. It uses
this to predict where the next instructions can be found in memory with an accuracy of 90 percent or greater. This is possible because while the processor is fetching instructions, it is also looking at instructions further ahead in the program.
Data Flow Analysis
Data flow analysis analyzes and schedules instructions to be executed in an optimal sequence,
independent of the original program order. The processor looks at decoded software instructions
and determines whether they are available for processing or are instead dependent on other
instructions to be executed first. The processor then determines the optimal sequence for processing and executes the instructions in the most efficient manner.
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Speculative Execution
Speculative execution increases performance by looking ahead of the program counter and executing instructions that are likely to be needed later. Because the software instructions being
processed are based on predicted branches, the results are stored in a pool for later referral. If they
are to be executed by the resultant program flow, the already completed instructions are retired
and the results are committed to the processor’s main registers in the original program execution
order. This technique essentially allows the processor to complete instructions in advance, and
then grab the already completed results when necessary.
Dual Independent Bus (DIB) Architecture
The Dual Independent Bus (DIB) architecture was first implemented in the first sixth-generation
processor. DIB was created to improve processor bus bandwidth and performance. Having two
(dual) independent data I/O buses enables the processor to access data from either of its buses
simultaneously and in parallel, rather than in a singular sequential manner (as in a single-bus
system). The second or backside bus in a processor with DIB is used for the L2 cache, allowing it
to run at much greater speeds than if it were to share the main processor bus.
Note
The DIB architecture is explained more fully in Chapter 4, “Motherboards and Buses.” To see the typical Pentium
system architecture, see Figure 4.34.
Two buses make up the DIB architecture: the L2 cache bus and the processor-to-main-memory, or
system, bus. The P6 class processors from the Pentium Pro to the Celeron and Pentium II/III
processors can use both buses simultaneously, eliminating a bottleneck there. The Dual
Independent Bus architecture enables the L2 cache of the 500MHz Celeron processor, for example, to run seven and a half times faster than the L2 cache of older Pentium processors. Because
the backside or L2 cache bus is coupled to the speed of the processor core, as the frequency of
future P6 class processors (Celeron, Pentium II/III) increases, so will the speed of the L2 cache.
The key to implementing DIB was to move the L2 cache memory off of the motherboard and
into the processor package. L1 cache has always been directly a part of the processor die, but L2
was larger and had to be external. By moving the L2 cache into the processor, the L2 cache could
run at speeds more like the L1 cache, much faster than the motherboard or processor bus. To
move the L2 cache into the processor initially, modifications had to be made to the CPU socket
or slot. There are two socket-based processors that fully support DIB. The Pentium Pro, which
plugs into Socket 8, and the Celeron, which is available in Socket 370 or Slot 1 versions. In the
Pentium Pro, the L2 cache is contained within the chip package but on separate die(s). This,
unfortunately, made the chip expensive and difficult to produce, although it did mean that the
L2 cache ran at full processor speed. The Celeron updates this design and includes both the L1
and L2 caches directly on the processor die. This allows the L1 and L2 to both run at full processor speed, and makes the chip much less expensive to produce.
The Pentium II/III adopted an initially less expensive and easier-to-manufacture approach called
the Single Edge Contact (SEC) or Single Edge Processor (SEP) package, which are covered in more
detail later in this chapter.
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Most Pentium II/III processors run the L2 cache at exactly 1/2-core speed, but that can easily be
scaled up or down in the future. For example the 300MHz and faster Pentium IIPE (Performance
Enhanced) processors used in laptop or mobile applications and the 600MHz Pentium III have
on-die L2 cache like the Celeron, which runs at full core speed. Also, most have 512KB of L2
cache internally, but the PII/III processors with on-die L2 cache only use 256KB. Even so, they are
faster than the 512KB versions, because it is better to have a cache that is twice as fast than one
that is twice as large.
Cache design can be easily changed in the future because Intel makes Xeon versions of the PII
and PIII that include 512KB, 1MB, or even 2MB of full core speed L2 cache. These aren’t on-die,
but consist of special high-speed Intel manufactured cache chips located within the cartridge. The
flexibility of the P6 processor design will allow Intel to make Pentium IIIs with any amount of
cache they like.
The Pentium II/III SEC processor connects to a motherboard via a single-edge connector instead
of the multiple pins used in existing Pin Grid Array (PGA) socket packages.
DIB also allows the system bus to perform multiple simultaneous transactions (instead of singular
sequential transactions), accelerating the flow of information within the system and boosting
performance. Overall DIB architecture offers up to three times the bandwidth performance over a
single-bus architecture processor.
Processor Manufacturing
Processors are manufactured primarily from silicon, the second most common element on
Earth—only oxygen is more abundant. Silicon is the primary ingredient in beach sand; however,
in that form it isn’t pure enough to be used in chips.
To be made into chips, raw silicon is purified, melted down, and then processed in special ovens
where a seed crystal is used to grow large cylindrical crystals called boules (see Figure 3.3). Each
boule is larger than eight inches in diameter and over 50 inches long, weighing hundreds of
pounds.
Seed Crystal
Boule
Molten Silicon
Figure 3.3
Growing a pure silicon boule in a high pressure, high temperature oven.
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The boule is then ground into a perfect 200mm-diameter cylindrical ingot (the current standard),
with a flat cut on one side for positioning accuracy and handling. Each ingot is then cut with a
high-precision diamond saw into over a thousand circular wafers, each less than a millimeter
thick (see Figure 3.4). Each wafer is polished to a mirror-smooth surface.
Shroud
Diamond
saw blade
Bed
Figure 3.4
Slicing a silicon ingot into wafers with a diamond saw.
Chips are manufactured from the wafers using a process called photolithography. Through this
photographic process, transistors and circuit and signal pathways are created in semiconductors
by depositing different layers of various materials on the chip, one after the other. Where two
specific circuits intersect, a transistor or switch can be formed.
The photolithographic process starts when an insulating layer of silicon dioxide is grown on the
wafer through a vapor deposition process. Then a coating of photoresist material is applied and
an image of that layer of the chip is projected through a mask onto the now light-sensitive surface.
Doping is the term used to describe chemical impurities added to silicon (which is naturally a
non-conductor), creating a material with semiconductor properties. The projector uses a specially
created mask, which is essentially a negative of that layer of the chip etched in chrome on a
quartz plate. The Pentium III currently uses five masks and has as many layers, although other
processors may have six or more layers. Each processor design requires as many masks as layers to
produce the chips.
As the light passes through the first mask, the light is focused on the wafer surface, imprinting it
with the image of that layer of the chip. Each individual chip image is called a die. A device
called a stepper then moves the wafer over a little bit and the same mask is used to imprint
another chip die immediately next to the previous one. After the entire wafer is imprinted with
chips, a caustic solution washes away the areas where the light struck the photoresist, leaving the
mask imprints of the individual chip vias (interconnections between layers) and circuit pathways.
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Then, another layer of semiconductor material is deposited on the wafer with more photoresist
on top, and the next mask is used to produce the next layer of circuitry. Using this method, the
layers of each chip are built one on top of the other, until the chips are completed.
The final masks add the metallization layers, which are the metal interconnects used to tie all the
individual transistors and other components together. Most chips use aluminum interconnects
today, although many will be moving to copper in the future. Copper is a better conductor than
aluminum and will allow smaller interconnects with less resistance, meaning smaller and faster
chips can be made. The reason copper hasn’t been used up until recently is that there were difficult corrosion problems to overcome during the manufacturing process that were not as much a
problem with aluminum.
A completed circular wafer will have as many chips imprinted on it as can possibly fit. Because
each chip is normally square or rectangular, there are some unused portions at the edges of the
wafer, but every attempt is made to use every square millimeter of surface.
The standard wafer size used in the industry today is 200mm in diameter, or just under 8 inches.
This results in a wafer of about 31,416 square millimeters. The current Pentium II 300MHz
processor is made up of 7.5 million transistors using a 0.35 micron (millionth of a meter) process.
This process results in a die of exactly 14.2mm on each side, which is 202 square millimeters of
area. This means that about 150 total Pentium II 300MHz chips on the .35 micron process can be
made from a single 200mm-diameter wafer.
The trend in the industry is to go to both larger wafers and a smaller chip die process. Process
refers to the size of the individual circuits and transistors on the chip. For example, the Pentium
II 333MHz and faster processors are made on a newer and smaller .25 micron process, which
reduces the total chip die size to only 10.2mm on each side, or a total chip area of 104 square
millimeters. On the same 200mm (8-inch) wafer as before, Intel can make about 300 Pentium II
chips using this process, or double the amount over the larger .35 micron process 300MHz version.
The Pentium III is currently built on a .25 micron process and has a die size of 128 square millimeters, which is about 11.3mm on each side. This is slightly larger than the Pentium II because
the III has about two million more transistors.
In the future, processes will move from .25 micron to .18, and then .13 micron. This will allow
for more than double the number of chips to be made on existing wafers, or more importantly,
will allow more transistors to be incorporated into the die, yet it will not be larger overall than
die today. This means the trend for incorporating L2 cache within the die will continue, and
transistor counts will rise up to 100 million per chip or more in the future.
The trend in wafers is to move from the current 200mm (8-inch) diameter to a bigger, 300mm
(12-inch) diameter wafer. This will increase surface area dramatically over the smaller 200mm
design and boost chip production to about 675 chips per wafer. Intel and other manufacturers
expect to have 300mm wafer production in place just after the year 2000. After that happens,
chip prices should continue to drop dramatically as supply increases.
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Note that not all the chips on each wafer will be good, especially as a new production line starts.
As the manufacturing process for a given chip or production line is perfected, more and more of
the chips will be good. The ratio of good to bad chips on a wafer is called the yield. Yields well
under 50 percent are common when a new chip starts production; however, by the end of a
given chip’s life, the yields are normally in the 90 percent range. Most chip manufacturers guard
their yield figures and are very secretive about them because knowledge of yield problems can
give their competitors an edge. A low yield causes problems both in the cost per chip and in
delivery delays to their customers. If a company has specific knowledge of competitors’ improving yields, they can set prices or schedule production to get higher market share at a critical
point. For example, AMD was plagued by low-yield problems during 1997 and 1998, which cost
them significant market share. They have been solving the problems, but it shows that yields are
an important concern.
After a wafer is complete, a special fixture tests each of the chips on the wafer and marks the bad
ones to be separated out later. The chips are then cut from the wafer using either a high-powered
laser or diamond saw.
After being cut from the wafers, the individual die are then retested, packaged, and retested
again. The packaging process is also referred to as bonding, because the die is placed into a chip
housing where a special machine bonds fine gold wires between the die and the pins on the chip.
The package is the container for the chip die, and it essentially seals it from the environment.
After the chips are bonded and packaged, final testing is done to determine both proper function
and rated speed. Different chips in the same batch will often run at different speeds. Special test
fixtures run each chip at different pressures, temperatures, and speeds, looking for the point at
which the chip stops working. At this point, the maximum successful speed is noted and the
final chips are sorted into bins with those that tested at a similar speed. For example, the
Pentium III 450, 500, and 550 are all exactly the same chip made using the same die. They were
sorted at the end of the manufacturing cycle by speed.
One interesting thing about this is that as a manufacturer gains more experience and perfects a
particular chip assembly line, the yield of the higher speed versions goes way up. This means that
out of a wafer of 150 total chips, perhaps more than 100 of them check out at 550MHz, while
only a few won’t run at that speed. The paradox is that Intel often sells a lot more of the lower
priced 450 and 500MHz chips, so they will just dip into the bin of 550MHz processors and label
them as 450 or 500 chips and sell them that way. People began discovering that many of the
lower-rated chips would actually run at speeds much higher than they were rated, and the business of overclocking was born. Overclocking describes the operation of a chip at a speed higher
than it was rated for. In many cases, people have successfully accomplished this because, in
essence, they had a higher-speed processor already—it was marked with a lower rating only
because it was sold as the slower version.
Intel has seen fit to put a stop to this by building overclock protection into most of their newer
chips. This is usually done in the bonding or cartridge manufacturing process, where the chips
are intentionally altered so they won’t run at any speeds higher than they are rated. Normally
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this involves changing the bus frequency (BF) pins on the chip, which control the internal multipliers the chip uses. Even so, enterprising individuals have found ways to run their motherboards
at bus speeds higher than normal, so even though the chip won’t allow a higher multiplier, you
can still run it at a speed higher than it was designed.
Be Wary of PII and PIII Overclocking Fraud
Also note that unscrupulous individuals have devised a small logic circuit that bypasses the overclock protection,
allowing the chip to run at higher multipliers. This small circuit can be hidden in the PII or PIII cartridge, and then
the chip can be remarked or relabeled to falsely indicate it is a higher speed version. This type of chip remarketing
fraud is far more common in the industry than people want to believe. In fact, if you purchase your system or
processor from a local computer flea market type show, you have an excellent chance of getting a remarked chip.
I recommend purchasing processors only from more reputable direct distributors or dealers. Contact Intel, AMD, or
Cyrix, for a list of their reputable distributors and dealers.
I recently installed a 200MHz Pentium processor in a system that is supposed to run at a 3x multiplier based off a 66MHz motherboard speed. I tried changing the multiplier to 3.5x but the chip
refused to go any faster; in fact, it ran at the same or lower speed than before. This is a sure sign
of overclock protection inside, which is to say that the chip won’t support any higher level of
multiplier. My motherboard included a jumper setting for an unauthorized speed of 75MHz,
which when multiplied by 3x resulted in an actual processor speed of 225MHz. This worked like
a charm, and the system is now running fast and clean. Note that I am not necessarily
recommending overclocking for everybody; in fact, I normally don’t recommend it at all for any
important systems. If you have a system you want to fool around with, it is interesting to try.
Like my cars, I always seem to want to hotrod my computers.
PGA Chip Packaging
PGA packaging has been the most common chip package used until recently. It was used starting
with the 286 processor in the 1980s and is still used today for Pentium and Pentium Pro processors. PGA takes its name from the fact that the chip has a grid-like array of pins on the bottom of
the package. PGA chips are inserted into sockets, which are often of a ZIF (Zero Insertion Force)
design. A ZIF socket has a lever to allow for easy installation and removal of the chip.
Most Pentium processors use a variation on the regular PGA called SPGA (Staggered Pin Grid
Array), where the pins are staggered on the underside of the chip rather than in standard rows
and columns. This was done to move the pins closer together and decrease the overall size of the
chip when a large number of pins is required. Figure 3.5 shows a Pentium Pro that uses the dualpattern SPGA (on the right) next to an older Pentium 66 that uses the regular PGA. Note that the
right half of the Pentium Pro shown here has additional pins staggered among the other rows
and columns.
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Single Edge Contact (SEC) and Single Edge Processor (SEP) Packaging
Figure 3.5
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71
PGA on Pentium 66 (left) and dual-pattern SPGA on Pentium Pro (right).
Single Edge Contact (SEC) and Single Edge
Processor (SEP) Packaging
Abandoning the chip-in-a-socket approach used by virtually all processors until this point, the
Pentium II/III chips are characterized by their Single Edge Contact (SEC) cartridge design. The
processor, along with several L2 cache chips, is mounted on a small circuit board (much like an
oversized memory SIMM), which is then sealed in a metal and plastic cartridge. The cartridge is
then plugged into the motherboard through an edge connector called Slot 1, which looks very
much like an adapter card slot.
By placing the processor and L2 cache as separate chips inside a cartridge, they now have a CPU
module that is easier and less expensive to make than the Pentium Pro that preceded it. The
Single Edge Contact (SEC) cartridge is an innovative—if a bit unwieldy—package design that
incorporates the backside bus and L2 cache internally. Using the SEC design, the core and L2
cache are fully enclosed in a plastic and metal cartridge. These subcomponents are surface
mounted directly to a substrate (or base) inside the cartridge to enable high-frequency operation.
The SEC cartridge technology allows the use of widely available, high-performance industry
standard Burst Static RAMs (BSRAMs) for the dedicated L2 cache. This greatly reduces the cost
compared to the proprietary cache chips used inside the CPU package in the Pentium Pro.
A less expensive version of the SEC is called the Single Edge Processor (SEP) package. The SEP
package is basically the same circuit board containing processor and (optional) cache as the
Pentium II, but without the fancy plastic cover. The SEP package plugs directly into the same Slot
1 connector used by the standard Pentium II. Four holes on the board allow for the heat sink to
be installed.
Slot 1 is the connection to the motherboard and has 242 pins. The Slot 1 dimensions are shown
in Figure 3.6. The SEC cartridge or SEP processor is plugged into Slot 1 and secured with a processor-retention mechanism, which is a bracket that holds it in place. There may also be a retention
mechanism or support for the processor heat sink. Figure 3.7 shows the parts of the cover that
make up the SEC package. Note the large thermal plate used to aid in dissipating the heat from
this processor. The SEP package is shown in Figure 3.8.
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132.87±.25
5.231±.010
72.00
2.832
R 0.25
.010
2.54±.127
.100±.005
47.00
1.850
2.50
.098
73 CONTACT PAIRS
2.50
.098
48 CONTACT PAIRS
1.88±.10
.074±.004
9.50±.25
.374±.010
1.27
.050
4.75
.187
1.78±.03
.070±.001
2.00±.127
.079±.005
76.13 (MIN)
2.997 (MIN)
Figure 3.6
51.13 (MIN)
2.013 (MIN)
Pentium II Processor Slot 1 dimensions (metric/English).
Top View
Cover
Left Latch
Right Latch
Left
Right
Cover Side View
Thermal Plate
Left
Right
Thermal Plate Side View
Skirt
Figure 3.7
Pentium II Processor SEC package parts.
Right
Side
.94
.037
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Single Edge Contact (SEC) and Single Edge Processor (SEP) Packaging
intel
Figure 3.8
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73
®
Celeron Processor SEP package front side view.
With the Pentium III, Intel introduced a variation on the SEC packaging called SECC2 (Single
Edge Contact Cartridge version 2). This new package covers only one side of the processor board
and allows the heat sink to directly attach to the chip on the other side. This direct thermal
interface allows for better cooling, and the overall lighter package is cheaper to manufacture.
Note that a new Universal Retention System, consisting of a new design plastic upright stand, is
required to hold the SECC2 package chip in place on the board. The Universal Retention System
will also work with the older SEC package as used on most Pentium II processors, as well as the
SEP package used on the slot based Celeron processors, making it the ideal retention mechanism
for all Slot 1-based processors. Figure 3.9 shows the SECC2 package.
Top view
Heat sink thermal
interface point
Substrate view
Figure 3.9
Side
view
Cover side view
SECC2 packaging used in newer Pentium II and III processors.
The main reason for going to the SEC and SEP packages in the first place was to be able to move
the L2 cache memory off the motherboard and onto the processor in an economical and scalable
way. Using the SEC/SEP design, Intel can easily offer Pentium II/III processors with more or less
cache and faster or slower cache.
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Processor Sockets
Intel has created a set of socket designs—Socket 1 through Socket 8, and the new Socket 370—
used for their chips from the 486 through the Pentium Pro and Celeron. Each socket is designed
to support a different range of original and upgrade processors. Table 3.9 shows the specifications
of these sockets.
Table 3.9
Socket
Number
Intel 486/Pentium CPU Socket Types and Specifications
Pins
Pin Layout
Voltage
Supported Processors
Socket 1
169
17×17 PGA
5v
486 SX/SX2, DX/DX2*, DX4 Overdrive
Socket 2
238
19×19 PGA
5v
486 SX/SX2, DX/DX2*, DX4 Overdrive,
486 Pentium Overdrive
Socket 3
237
19×19 PGA
5v/3.3v
486 SX/SX2, DX/DX2, DX4,
486 Pentium Overdrive, AMD 5x86
Pentium 60/66, Overdrive
Socket 4
273
21×21 PGA
5v
Socket 5
320
37×37 SPGA
3.3/3.5v
Pentium 75-133, Overdrive
Socket 6**
235
19×19 PGA
3.3v
486 DX4, 486 Pentium Overdrive
Socket 7
321
37×37 SPGA
VRM
Pentium 75-233+, MMX, Overdrive,
AMD K5/K6, Cyrix M1/II
Socket 8
387
dual pattern SPGA
Auto VRM
Pentium Pro
PGA370
370
37×37 SPGA
Auto VRM
Celeron
Slot 1
242
Slot
Auto VRM
Pentium II/III, Celeron
Slot 2
330
Slot
Auto VRM
Pentium II/III Xeon
*Non-overdrive DX4 or AMD 5x86 also can be supported with the addition of an aftermarket 3.3v
voltage-regulator adapter.
**Socket 6 was a paper standard only and was never actually implemented in any systems.
PGA = Pin Grid Array.
SPGA = Staggered Pin Grid Array.
VRM = Voltage Regulator Module.
Sockets 1, 2, 3, and 6 are 486 processor sockets and are shown together in Figure 3.10 so you can
see the overall size comparisons and pin arrangements between these sockets. Sockets 4, 5, 7, and
8 are Pentium and Pentium Pro processor sockets and are shown together in Figure 3.11 so you
can see the overall size comparisons and pin arrangements between these sockets. More detailed
drawings of each socket are included throughout the remainder of this section with the thorough
descriptions of the sockets.
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Processor Sockets
Socket 1
Figure 3.10
Socket 4
Figure 3.11
Socket 2
Socket 3
Chapter 3
75
Socket 6
486 processor sockets.
Socket 5
Socket 7
Socket 8
Pentium and Pentium Pro processor sockets.
Socket 1
The original OverDrive socket, now officially called Socket 1, is a 169-pin PGA socket.
Motherboards that have this socket can support any of the 486SX, DX, and DX2 processors, and
the DX2/OverDrive versions. This type of socket is found on most 486 systems that originally
were designed for OverDrive upgrades. Figure 3.12 shows the pinout of Socket 1.
The original DX processor draws a maximum 0.9 amps of 5v power in 33MHz form (4.5 watts)
and a maximum 1 amp in 50MHz form (5 watts). The DX2 processor, or OverDrive processor,
draws a maximum 1.2 amps at 66MHz (6 watts). This minor increase in power requires only a
passive heat sink consisting of aluminum fins that are glued to the processor with thermal transfer epoxy. Passive heat sinks don’t have any mechanical components like fans. Heat sinks with
fans or other devices that use power are called active heat sinks. OverDrive processors rated at
40MHz or less do not have heat sinks.
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17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
A6
VSS
A10
VSS
VSS
VSS
VSS
VSS
A12
VSS
A14
NC
A23
A26
A27
NC BLAST# A3
VCC
A8
A11
VCC
VCC
VCC
VCC
A15
VCC
A18
VSS
VCC
A25
A28
ADS#
A4
S
S
R
R
PCHK# PLOCK# BREQ A2
A7
A5
A9
A13
A16
A20
A22
A24
A21
A19
A17
VSS
A31
A30
A29
D0
DPO
D1
D2
Q
VSS
VCC HLDA
Q
P
P
W/R# M/10# LOCK#
N
N
VSS
VCC
D/C#
D4
VCC
VSS
VSS
VCC
PWT
D7
D6
VSS
VSS
VCC BEO#
D14
VCC
VSS
M
L
M
L
K
K
Socket 1
PCD
BE1# BE2#
D16
D5
VCC
VSS
VCC BRDY#
DP2
D3
VSS
VSS
VCC
D12
VCC
VSS
D15
D8
DP1
D10
VCC
VSS
J
H
J
NC
G
G
BE3# RDY# KEN#
F
F
VSS
VCC HOLD
E
E
BOFF# BS8# A20M#
KEY
D17
D13
D9
NC
NC
NC
NC
D30
D28
D26
D27
VCC
VCC
CLK
D18
D11
NC
NC
VCC
NC
VCC
D31
VCC
D25
VSS
VSS
VSS
D21
D19
AHOLD INTR IGNNE# NC FERR# NC
VSS
NC
VSS
D29
VSS
D24
DP3
D23
NC
D22
D20
9
8
7
6
5
4
3
2
1
D
D
BS16# RESET FLUSH # NC
C
C
EADS# NC
NMI
UP#
B
B
A
17 16 15 14 13 12 11 10
Figure 3.12
H
A
Intel Socket 1 pinout.
Socket 2
When the DX2 processor was released, Intel was already working on the new Pentium processor.
The company wanted to offer a 32-bit, scaled-down version of the Pentium as an upgrade for systems that originally came with a DX2 processor. Rather than just increasing the clock rate, Intel
created an all new chip with enhanced capabilities derived from the Pentium.
The chip, called the Pentium OverDrive processor, plugs into a processor socket with the Socket 2
or Socket 3 design. These sockets will hold any 486 SX, DX, or DX2 processor, as well as the
Pentium OverDrive. Because this chip is essentially a 32-bit version of the (normally 64-bit)
Pentium chip, many have taken to calling it a Pentium-SX. It is available in 25/63MHz and
33/83MHz versions. The first number indicates the base motherboard speed; the second number
indicates the actual operating speed of the Pentium OverDrive chip. As you can see, it is a clockmultiplied chip that runs at 2.5 times the motherboard speed. Figure 3.13 shows the pinout configuration of the official Socket 2 design.
Notice that although the new chip for Socket 2 is called Pentium OverDrive, it is not a full-scale
(64-bit) Pentium. Intel released the design of Socket 2 a little prematurely and found that the
chip ran too hot for many systems. The company solved this problem by adding a special active
heat sink to the Pentium OverDrive processor. This active heat sink is a combination of a standard heat sink and a built-in electric fan. Unlike the aftermarket glue-on or clip-on fans for
processors that you might have seen, this one actually draws 5v power directly from the socket to
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77
drive the fan. No external connection to disk drive cables or the power supply is required. The
fan/heat sink assembly clips and plugs directly into the processor and provides for easy replacement if the fan fails.
A
B
C
D
E
F
G
H
J
K
L
M
N
P
Q
R
S
T
U
NC
RES
VSS
VCC
VSS
INIT
VSS
VSS
VCC
VCC
VCC
VSS
VSS
RES
VSS
VCC
VSS
RES
RES
BE3#
VSS
VSS
PCD
VSS
VSS
VSS
W/R#
VSS PCHK# INC
VCC
VCC M/10# VCC PLOCK# BLAST# A4
VSS
19
19
18
RES AHOLD EADS# BS16# BOFF# VSS
ADS# RES
17
17
VSS
16
INTR
RES RESET BS8#
VCC
RDY#
VCC
VCC
BE1#
VCC
VCC IGNNE# NMI FLUSH# A20M# HOLD KEN# STPCLK# BRDY# BE2# BE0# PWT
D/C# LOCK# HLDA BREQ
A3
A6
VCC
VSS
PLUG PLUG PLUG
A2
VCC
VSS
VSS
15
14
13
12
11
10
UP#
VSS FERR# INC
INC
PLUG PLUG PLUG
NC
PLUG
PLUG
A7
A8
A10
VSS
PLUG
A5
A11
VSS
VSS
A9
VCC
VSS
VSS
A13
VCC
VSS
VCC
5
4
3
2
14
VSS
INC
INC SMIACT# PLUG
VSS
VSS
VCC
INC
VCC
INC
SMI#
INC
VCC
VSS
VCC
D30
A16
VCC
VSS
VCC
VCC
D29
D31
D28
A20
VCC
VSS
VCC
A22
A15
A12
VSS
Socket 2
8
6
VSS
VSS
VCC
D26
RES
D24
D25
D27
PLUG
PLUG
A24
VCC
VSS
VSS
RES
DP3
VSS
VCC
PLUG
PLUG
A21
A18
A14
VSS
VSS
D23
VSS
VCC
KEY PLUG PLUG
PLUG PLUG PLUG
A19
VSS
INC
VSS
VCC
RES
VSS
CLK
D17
D10
D15
D12
DP2
D16
D14
D7
D4
DP0
A30
A17
VCC
A23
VCC
D21
D18
D13
VCC
D8
VCC
D3
D5
VCC
D6
VCC
D1
A29
VSS
A25
A26
VSS
D19
D11
D9
VSS
DP1
VSS
VSS
VCC
VSS
VSS
VSS
D2
D0
A31
A28
A27
RES
VSS
VCC
VSS
RES
RES
VSS
VCC
VCC
VCC
VSS
RES
RES
VSS
VCC
VSS
RES
RES
C
D
E
F
G
H
J
K
L
M
N
P
Q
R
S
T
U
VSS
PLUG
D22
D20
1
13
12
11
10
9
8
7
6
5
4
3
2
1
PLUG PLUG
A
Figure 3.13
16
15
RES
9
7
18
B
238-pin Intel Socket 2 configuration.
Another requirement of the active heat sink is additional clearance—no obstructions for an area
about 1.4 inches off the base of the existing socket to allow for heat-sink clearance. The Pentium
OverDrive upgrade will be difficult or impossible in systems that were not designed with this feature.
Another problem with this particular upgrade is power consumption. The 5v Pentium OverDrive
processor will draw up to 2.5 amps at 5v (including the fan) or 12.5 watts, which is more than
double the 1.2 amps (6 watts) drawn by the DX2 66 processor. Intel did not provide this information when it established the socket design, so the company set up a testing facility to certify systems for thermal and mechanical compatibility with the Pentium OverDrive upgrade. For the
greatest peace of mind, ensure that your system is certified compatible before you attempt this
upgrade.
Note
See Intel’s Web site (http://www.intel.com) for a comprehensive list of certified OverDrive-compatible
systems.
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Figure 3.14 shows the dimensions of the Pentium OverDrive processor and the active heat
sink/fan assembly.
Required Airspace
0.20"
1.963"
1.840"
0.40"
1.370"
OverDrive Processor
Active Fan/Heat Sink Unit
Adhesive
OverDrive Processor PGA Package
Figure 3.14
0.800" 0.970"
0.010"
0.160"
The physical dimensions of the Intel Pentium OverDrive processor and active heat sink.
Socket 3
Because of problems with the original Socket 2 specification and the enormous heat the 5v version of the Pentium OverDrive processor generates, Intel came up with an improved design. The
new processor is the same as the previous Pentium OverDrive processor, except that it runs on
3.3v and draws a maximum 3.0 amps of 3.3v (9.9 watts) and 0.2 amp of 5v (1 watt) to run the
fan—a total 10.9 watts. This configuration provides a slight margin over the 5v version of this
processor. The fan will be easy to remove from the OverDrive processor for replacement, should it
ever fail.
Intel had to create a new socket to support both the DX4 processor, which runs on 3.3v, and the
3.3v Pentium OverDrive processor. In addition to the new 3.3v chips, this new socket supports
the older 5v SX, DX, DX2, and even the 5v Pentium OverDrive chip. The design, called Socket 3,
is the most flexible upgradable 486 design. Figure 3.15 shows the pinout specification of Socket 3.
Notice that Socket 3 has one additional pin and several others plugged compared with Socket 2.
Socket 3 provides for better keying, which prevents an end user from accidentally installing the
processor in an improper orientation. However, one serious problem exists: This socket cannot
automatically determine the type of voltage that will be provided to it. A jumper is likely to be
added on the motherboard near the socket to enable the user to select 5v or 3.3v operation.
Caution
Because this jumper must be manually set, however, a user could install a 3.3v processor in this socket when it is
configured for 5v operation. This installation will instantly destroy a very expensive chip when the system is powered on. So, it is up to the end user to make sure that this socket is properly configured for voltage, depending on
which type of processor is installed. If the jumper is set in 3.3v configuration and a 5v processor is installed, no
harm will occur, but the system will not operate properly unless the jumper is reset for 5v.
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A
B
C
D
E
F
G
H
J
K
L
M
N
P
Q
R
S
T
U
NC
RES
VSS
VCC
VSS
INIT
VSS
VSS
VCC
VCC
VCC
VSS
VSS
RES
VSS
VCC
VSS
RES
RES
RES AHOLD EADS# BS16# BOFF# VSS
BE3#
VSS
VSS
PCD
VSS
VSS
VSS
W/R#
VSS PCHK# INC
VSS
RDY#
VCC
VCC
BE1#
VCC
VCC
VCC M/10# VCC PLOCK# BLAST# A4
VSS
A3
A6
VCC
19
19
18
ADS# RES
17
16
13
12
11
10
RES RESET BS8#
VCC
VCC IGNNE# NMI FLUSH# A20M# HOLD KEN# STPCLK# BRDY# BE2# BE0# PWT
D/C# LOCK# HLDA BREQ
VSS
PLUG PLUG PLUG
A2
VCC
VSS
VSS
UP#
VSS FERR# INC
INC
PLUG PLUG PLUG
NC
PLUG
PLUG
A7
A8
A10
VSS
PLUG
A5
A11
VSS
VSS
A9
VCC
VSS
VSS
A13
VCC
VSS
VCC
5
4
3
2
14
VSS
INC
INC SMIACT# PLUG
VSS
VSS
VCC
INC
VCC
INC
SMI#
INC
VCC
VSS
VCC
D30
A16
VCC
VSS
VCC
VCC
D29
D31
D28
A20
VCC
VSS
VCC
VSS
VSS
VCC
D26
A22
A15
A12
VSS
RES
D24
D25
D27
PLUG
PLUG
A24
VCC
VSS
VSS
RES
DP3
VSS
VCC
PLUG
PLUG
A21
A18
A14
VSS
VSS
D23
VSS
VCC
KEY PLUG PLUG
PLUG PLUG PLUG
A19
VSS
INC
VSS
VCC
RES
VSS
CLK
D17
D10
VCC
A23
VCC
Socket 3
8
6
D15
D12
DP2
D16
D14
D7
D4
DP0
A30
A17
PLUG D22
D21
D18
D13
VCC
D8
VCC
D3
D5
VCC
D6
VCC
D1
A29
VSS
A25
A26
VSS
PLUG
D19
D11
D9
VSS
DP1
VSS
VSS
VCC
VSS
VSS
VSS
D2
D0
A31
A28
A27
RES
VSS
RES
RES
VSS
VCC
VCC
VCC
VSS
RES
RES
VSS
VCC
VSS
RES
RES
E
F
G
H
J
K
L
M
N
P
Q
R
S
T
U
D20
1
13
12
11
10
9
8
7
6
5
4
3
2
1
KEY PLUG PLUG VCC
A
Figure 3.15
16
15
RES
9
7
18
17
INTR
15
14
79
B
C
D
237-pin Intel Socket 3 configuration.
Socket 4
Socket 4 is a 273-pin socket that was designed for the original Pentium processors. The original
Pentium 60MHz and 66MHz version processors had 273 pins and would plug into Socket 4—a
5v-only socket, because all the original Pentium processors run on 5v. This socket will accept the
original Pentium 60MHz or 66MHz processor, and the OverDrive processor. Figure 3.16 shows the
pinout specification of Socket 4.
Somewhat amazingly, the original Pentium 66MHz processor consumes up to 3.2 amps of 5v
power (16 watts), not including power for a standard active heat sink (fan). The 66MHz
OverDrive processor that replaced it consumes a maximum 2.7 amps (13.5 watts), including
about 1 watt to drive the fan. Even the original 60MHz Pentium processor consumes up to 2.91
amps at 5v (14.55 watts). It might seem strange that the replacement processor, which is twice as
fast, consumes less power than the original, but this has to do with the manufacturing processes
used for the original and OverDrive processors.
Although both processors will run on 5v, the original Pentium processor was created with a circuit size of 0.8 micron, making that processor much more power-hungry than the newer 0.6
micron circuits used in the OverDrive and the other Pentium processors. Shrinking the circuit
size is one of the best ways to decrease power consumption. Although the OverDrive processor
for Pentium-based systems will draw less power than the original processor, additional clearance
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may have to be allowed for the active heat sink assembly that is mounted on top. As in other
OverDrive processors with built-in fans, the power to run the fan will be drawn directly from the
chip socket, so no separate power-supply connection is required. Also, the fan will be easy to
replace should it ever fail.
1
A
B
C
D
E
F
G
H
J
K
L
M
INV
IV
2
3
4
M/10# EWBE# VCC
BP2
BP3
D6
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21
VCC
VCC
VCC
VCC
DP2
D23
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
DP5
D43
D45
VSS
VSS
VSS
VSS
D17
D24
VSS
VSS
VSS
VSS
VSS
VSS
VSS
VSS
D41
D47
D48
B
C
VCC IERR# PM1/BP1 D4
DP1
D18
D22
D25
D29
D31
D26
D9
D10
D12
D19
D21
D33
D36
D34
D50
D52
VCC PMO/BPO D0
D13
D15
D16
D20
DP3
D27
D32
D28
D30
D14
D40
D39
D37
D35
DP4
D38
D42
D44
VCC
VSS
D1
D2
D11
Plug
D46
DP6
D54
DP7
VCC
VSS
D3
D8
D51
D49
D57
VCC
VCC
VSS
D5
D7
D53
D55
VSS
VCC
VCC
VSS FERR# DPO
D63
D59
VSS
D56
VSS
IU
KEN# CACHE#
D58
D62
VSS
VCC
VSS
VSS
NA# BOFF#
CLK
D61
VSS
VCC
RESET D60
VSS
VCC
Socket 4
VSS AHOLD NC BRDY#
A
D
E
F
G
H
J
K
L
M
VSS WB/WT# EADS# HITM#
PEN# FRCMC# VSS
VCC
VCC
VSS
W/R#
NC
INTR
NMI
VSS
VCC
P
VCC
VSS
AP
ADS#
SMI#
TMS
VSS
VCC
P
Q
VCC VSS
HLDA BE1#
VCC
NC
VSS
VCC
Q
R
VCC
VSS PCHK# SCYC
R/S#
NC
VSS
VCC
R
S
VCC
VSS
NC IGNNE# TDO
S
T
VCC VSS BUSCHK# TCK SMIACT# BE4#
U
V
N
W
Plug
Plug TRST#
BT0
A26
A19
A17
A15
A13
A11
A9
A7
A3
NC
IBT
INIT
TDI
T
VCC FLUSH# PRDY BE0# A20M# BE2# BE6#
A24
A22
A20
A18
A16
A14
A12
A10
A8
A6
A5
A25
A23
A21
U
BE3# BREQ LOCK# D/C# HOLD
VSS
VSS
VSS
VSS
VSS
VSS
VSS
VSS
VSS
VSS
VSS
A31
A29
A27
V
BT1
W
BE7# HIT# APCHK# PCD
1
Figure 3.16
PWT BE5#
N
2
3
4
A28
BT2
VSS
A30
VCC
VCC
VCC
VCC
5
6
7
8
9
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
A4
BT3
10 11 12 13 14 15 16 17 18 19 20 21
273-pin Intel Socket 4 configuration.
Socket 5
When Intel redesigned the Pentium processor to run at 75, 90, and 100MHz, the company went
to a 0.6 micron manufacturing process and 3.3v operation. This change resulted in lower power
consumption: only 3.25 amps at 3.3v (10.725 watts). Therefore, the 100MHz Pentium processor
can use far less power than even the original 60MHz version. The newest 120 and higher
Pentium, Pentium Pro, and Pentium II chips use an even smaller die 0.35 micron process. This
results in lower power consumption and allows the extremely high clock rates without overheating.
The Pentium 75 and higher processors actually have 296 pins, although they plug into the official Intel Socket 5 design, which calls for a total 320 pins. The additional pins are used by the
Pentium OverDrive for Pentium processors. This socket has the 320 pins configured in a staggered Pin Grid Array, in which the individual pins are staggered for tighter clearance.
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81
Several OverDrive processors for existing Pentiums are currently available. If you have a first-generation Pentium 60 or 66 with a Socket 4, you can purchase a standard Pentium OverDrive chip
that effectively doubles the speed of your old processor. An OverDrive chip with MMX technology is available for second-generation 75MHz, 90MHz, and 100MHz Pentiums using Socket 5 or
Socket 7. Processor speeds after upgrade are 125MHz for the Pentium 75, 150MHz for the
Pentium 90, and 166MHz for the Pentium 100. MMX greatly enhances processor performance,
particularly under multimedia applications, and is discussed in the section “Pentium-MMX
Processors,” later in this chapter. Figure 3.17 shows the standard pinout for Socket 5.
The Pentium OverDrive for Pentium processors has an active heat sink (fan) assembly that draws
power directly from the chip socket. The chip requires a maximum 4.33 amps of 3.3v to run the
chip (14.289 watts) and 0.2 amp of 5v power to run the fan (1 watt), which means total power
consumption of 15.289 watts. This is less power than the original 66MHz Pentium processor
requires, yet it runs a chip that is as much as four times faster!
1 2
3
4 5 6
PLUG
VSS
D41
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
D22
D18
D15
NC
A
A
VCC
B
C
INC
D47
D52
G
H
J
VCC
L
N
R
S
U
W
Y
Z
AA
AE
AF
AG
AH
AJ
AL
AM
AN
VCC
NC
D30
VSS
D28
VCC
D24
D26
VSS
D23
NC
D21
D19
VCC
D16
D17
DP1
VSS
EWBE#
PICD0
D60
VCC
DP7
TDO
TCK
VCC
Socket 5
HLDA
INIT
A23
NC
A27
PLUG
ADS#
PLUG
VSS
HIT#
VSS
A20M#
EADS#
W/R#
VCC5
INC
3
4 5 6
VSS
FLUSH#
VCC
BE1#
HITM# BUSCHK# BE0#
VSS
VCC
VSS
BE3#
BE2#
VSS
VCC
NC
BE5#
BE4#
VSS
VCC
VSS
BE7#
BE6#
VSS
VCC
CLK
SCYC
VCC
VSS
VCC
VSS
RESET
NC
NC
VSS
VCC
VSS
A17
A18
VSS
VCC
VSS
A19
A20
A15
A16
VSS
VCC
VCC
A13
A14
VSS
VCC
VSS
VCC
VSS
A9
A12
VSS
VCC
A31
A5
A11
A8
A10
AB
AD
VCC
A25
VSS
A28
A3
A4
A6
AC
A22
A29
A7
VCC
VCC
A26
320-pin Intel Socket 5 configuration.
AF
AG
AH
AJ
AL
AM
VSS
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
Socket 5
AE
AK
VSS
A30
NC
Y
Z
AA
VSS
A24
W
VCC
VSS
A21
U
X
VSS
RS#
INTR
PCD
VCC
VSS
SMI#
NMI
R
S
V
VSS
IGNNE#
Q
T
VCC
FRCMC# VCC
PEN#
DC#
PWT
ADSC#
VCC5
NC
NC
BF
PCHK#
AP
INC
VSS
NC
PRDY
LOCK#
VCC
VSS
STPCLK# VSS
PBREO# APCHK#
BREQ
NC
N
P
VSS
VCC
J
L
M
VCC
VSS
NC
G
H
K
VCC
VSS
TDI
NC
HOLD
VSS
VCC
TRST# CPUTYP VCC
NA#
SMIACT#
VSS
PICD1
E
F
VCC
VSS
TMS
PBGNT#
VSS
VCC
D2
D0
C
D
D4
D1
PICCLK
KEN#
PHITM#
VSS
VCC
D6
D5
D3
PLUG
B
D9
DP0
D7
BOFF#
VSS
VCC
D8
VSS
PHIT# WB/WT#
VCC
D10
D12
BRDY#
VSS
D11
D14
PLUG
INV
BRDYC#
VCC
D13
AHOLD
VSS
VCC
1 2
Figure 3.17
DP2
D20
BP3
CACHE#
VCC
AK
VSS
DP3
D25
VSS
MI/O#
VSS
AD
VSS
D33
D27
VSS
PM1BP1
BP2
VCC
AB
AC
D42
D35
D29
VSS
IERR#
VSS
X
D37
D31
VSS
PM0BP0 FERR#
VCC
V
D39
D32
VSS
D62
D63
VSS
T
D40
D34
VSS
D58
D61
VCC
D36
VSS
D59
VSS
P
Q
D57
VCC
VSS
DP5
D56
VSS
M
VSS
D53
VSS
VCC
VSS
D38
D46
D51
D55
VSS
K
D44
D49
DP6
VCC
VSS
DP4
D48
D54
F
VSS
D45
D50
D
E
D43
AN
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Socket 6
The last 486 socket was created especially for the DX4 and the 486 Pentium OverDrive processor.
Socket 6 is a slightly redesigned version of Socket 3, which has an additional two pins plugged for
proper chip keying. Socket 6 has 235 pins and will accept only 3.3v 486 or OverDrive processors.
This means that Socket 6 will accept only the DX4 and the 486 Pentium OverDrive processor.
Because this socket provides only 3.3v, and because the only processors that plug into it are
designed to operate on 3.3v, there’s no chance that damaging problems will occur, such as those
with the Socket 3 design. In practice, Socket 6 has seen very limited use. Figure 3.18 shows the
Socket 6 pinout.
A
B
C
D
E
F
G
H
J
K
L
M
N
P
Q
R
S
T
U
VSS
VCC
VSS
INIT
VSS
VSS
VCC
VCC
VCC
VSS
VSS
RES
VSS
VCC
VSS
RES
RES
RES AHOLD EADS# BS16# BOFF# VSS
BE3#
VSS
VSS
PCD
VSS
VSS
VSS
W/R#
VSS PCHK# INC
VSS
RDY#
VCC
VCC
BE1#
VCC
VCC
VCC M/10# VCC PLOCK# BLAST# A4
VSS
A3
A6
VCC
19
19
PLUG RES
18
ADS# RES
17
16
17
INTR
RES RESET BS8#
VCC
VCC IGNNE# NMI FLUSH# A20M# HOLD KEN# STPCLK# BRDY# BE2# BE0# PWT
D/C# LOCK# HLDA BREQ
VSS
15
14
13
12
11
10
UP#
INC
PLUG PLUG PLUG
PLUG PLUG PLUG
A2
VCC
VSS
VSS
NC
PLUG
PLUG
A7
A8
A10
VSS
PLUG
A5
A11
VSS
VSS
A9
VCC
VSS
VSS
A13
VCC
VSS
VCC
5
4
3
2
14
VSS
INC
INC SMIACT# PLUG
VSS
VSS
VCC
INC
VCC
INC
SMI#
INC
VCC
VSS
VCC
D30
A16
VCC
VSS
VCC
VCC
D29
D31
D28
A20
VCC
VSS
VCC
VSS
VSS
VCC
D26
A22
A15
A12
VSS
RES
D24
D25
D27
Socket 6
8
6
PLUG
PLUG
A24
VCC
VSS
VSS
PLUG
PLUG
A21
A18
A14
VSS
PLUG PLUG PLUG
A19
VSS
INC
VSS
RES
DP3
VSS
VCC
VSS
D23
VSS
VCC PLUG PLUG PLUG
VCC
RES
VSS
CLK
D17
D10
D15
D12
DP2
D16
D14
D7
D4
DP0
A30
A17
VCC
A23
VCC
D18
D13
VCC
D8
VCC
D3
D5
VCC
D6
VCC
D1
A29
VSS
A25
A26
VSS
D11
D9
VSS
DP1
VSS
VSS
VCC
VSS
VSS
VSS
D2
D0
A31
A28
A27
RES
VSS
RES
RES
VSS
VCC
VCC
VCC
VSS
RES
RES
VSS
VCC
VSS
RES
RES
E
F
G
H
J
K
L
M
N
P
Q
R
S
T
U
PLUG D22
PLUG
D20
D21
D19
1
13
12
11
10
9
8
7
6
5
4
3
2
1
KEY PLUG PLUG VCC
A
Figure 3.18
16
15
RES
VSS FERR# INC
9
7
18
B
C
D
235-pin Intel Socket 6 configuration.
Socket 7 (and Super7)
Socket 7 is essentially the same as Socket 5 with one additional key pin in the opposite inside
corner of the existing key pin. Socket 7, therefore, has 321 pins total in a 21×21 SPGA arrangement. The real difference with Socket 7 is not the socket but with the companion VRM (Voltage
Regulator Module) that must accompany it.
The VRM is a small circuit board that contains all the voltage regulation circuitry used to drop
the 5v power supply signal to the correct voltage for the processor. The VRM was implemented
for several good reasons. One is that voltage regulators tend to run hot and are very failure-prone.
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83
Soldering these circuits on the motherboard, as has been done with the Pentium Socket 5 design,
makes it very likely that a failure of the regulator will require a complete motherboard replacement. Although technically the regulator could be replaced, many are surface-mount soldered,
which would make the whole procedure very time-consuming and expensive. Besides, in this day
and age, when the top-of-the-line motherboards are worth only $150, it is just not cost-effective
to service them. Having a replaceable VRM plugged into a socket will make it easy to replace the
regulators should they ever fail.
Although replacability is nice, the main reason behind the VRM design is that Intel and other
manufacturers have built Pentium processors to run on a variety of voltages. Intel has several different versions of the Pentium and Pentium-MMX processors that run on 3.3v (called VR),
3.465v (called VRE), or 2.8v, while AMD, Cyrix and others use different variations. Because of
this, most newer motherboard manufacturers are either including VRM sockets or building adaptable VRMs into the motherboard.
Figure 3.19 shows the Socket 7 pinout.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
A
VSS D41 VCC2 VCC2 VCC2 VCC2 VCC2 VCC2 VCC3 VCC3 VCC3 VCC3 VCC3 VCC3 D22 D18 D15
NC
B
VCC2 D43 VSS VSS VSS VSS
VSS VSS VSS VSS
VSS VSS VSS VSS D20 D16 D13 D11
C
D32 D31 D29 D27
D25 DP2 D24
D21 D17 D14 D10
D9
D INC D47 D45 DP4 D38 D36 D34
D50 D48 D44 D40 D39 D37
D35 D33 DP3 D30
D28 D26 D23
D19 DP1 D12
D8
DP0
E
D54
D52
D49
D46
D42
VSS
VSS
VCC2
NC
VSS
VCC3
VSS
NC
VCC3
VSS
VSS
D
7
D
6
VCC3
F
DP6 D51 DP5
D5
D4
G
VCC2 D55 D53
D3
D1 VCC3
H
VSS D56
PICCLK VSS
J
VCC2 D57 D58
PICD0 D2 VCC3
K
VSS D59
D0
VSS
L
VCC2 D61 D60
VCC3 PICD1 VCC3
M
VSS D52
TCK VSS
N
VCC2 D63 DP7
TD0 TDI VCC3
P
VSS IERR#
TMS# VSS
Q
VCC2 PM0BP0 FERR#
TRST# CPUTYP VCC3
R
VSS PM1BP1
NC
VSS
S
VCC2 BP2 BP3
NC
NC VCC3
T
VSS M/0#
VCC3 VSS
U
VCC2 CACHE# INV
VCC3 VSS VCC3
V
VSS AHOLD
STPCLK# VSS
W
VCC2 EWBE# KEN#
NC
NC VCC3
X
VSS BRDY#
BF1 VSS
Y
VCC2 BRDYC# NA#
BF FRCMC# VCC3
Z
VSS B0FF#
PEN# VSS
AA
VCC2 PHIT# WB/WT#
INIT IGNNE# VCC3
AB
VSS HOLD
SMI# VSS
AC
VCC2 PHITM# PRDY
NMI RS# VCC3
AD
VSS PBGNT#
INTR VSS
AE
VCC2 PBREQ# APCHK#
A23 D/P# VCC3
AF
VSS PCHK#
A21 VSS
AG
VCC2 SMIACT# PCD
A27 A24 VCC3
AH
VSS LOCK#
KEY A26 A22
AJ
BREQ HLDA ADS# VSS VSS VCC2 VSS
NC
VSS VCC3 VSS
NC VSS VSS VCC3 VSS A31 A25 VSS
AK
AP D/C# HIT# A20M# BE1# BE3# BE5# BE7# CLK RESET A19 A17
A15
A13
A9
A5
A29 A28
AL
VCC2DET PWT HITM# BUSCHK# BE0# BE2# BE4# BE6# SCYC NC A20
A18 A16
A14
A12
A11
A7
A3
VSS
AM
ADSC# EADS# W/R# VSS VSS VSS
VSS VSS VSS VSS
VSS VSS VSS VSS VSS
A8
A4
A30
AN
VCCS VCCS INC FLUSH# VCC2 VCC2 VCC2 VCC2 VCC2 VCC2 VCC3 VCC3 VCC3 VCC3 VCC3 A10
A6
NC
VSS
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚
Figure 3.19
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚ ˚ ˚
˚ ˚
˚
˚
˚ ˚
˚ ˚ ˚
˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚
A
B
C
D
E
F
G
H
J
K
L
M
N
P
Q
R
S
T
U
V
W
X
Y
Z
AA
AB
AC
AD
AE
AF
AG
AH
AJ
AK
AL
AM
AN
Socket 7 (Pentium) Pinout (top view).
AMD, along with Cyrix and several chipset manufacturers, pioneered an improvement or extension to the Intel Socket 7 design called Super Socket 7 (or Super7), taking it from 66MHz to
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95MHz and 100MHz. This allows for faster Socket 7 type systems to be made, which are nearly as
fast as the newer Slot 1 and Socket 370 type systems using Intel processors. Super7 systems also
have support for the AGP video bus, as well as Ultra-DMA hard disk controllers, and advanced
power management.
New chipsets are required for Super7 boards. Major third-party chipset suppliers, including Acer
Laboratories Inc. (Ali), VIA Technologies, and SiS, are supporting the Super7 platform. ALi has the
Aladdin V, VIA the Apollo MVP3, and SiS the SiS530 chipset for Super7 boards. Most of the major
motherboard manufacturers are making Super7 boards in both Baby-AT and ATX form factors.
If you want to purchase a Pentium class board that can be upgraded to the next generation of
even higher speed Socket 7 processors, look for a system with a Super7 socket and an integrated
VRM that supports different voltage selections.
Socket 8
Socket 8 is a special SPGA socket featuring a whopping 387 pins! This was specifically designed
for the Pentium Pro processor with the integrated L2 cache. The additional pins are to allow the
chipset to control the L2 cache that is integrated in the same package as the processor. Figure
3.20 shows the Socket 8 pinout.
47 45 43 41 39 37 35 33 31 29 27 25 23 21 19 17 15 13 11 9 7 5 3 1
BC
BA
AY
AW
AU
AS
AQ
AN
AL
AJ
AG
AF
AE
AC
AB
AA
Y
X
W
U
T
S
Q
P
N
L
K
J
G
F
E
C
B
A
ew
p
To
Vi
2H2O
BC
BA
AY
AW
AU
AS
AQ
AN
AL
AJ
AG
AF
AE
AC
AB
AA
Y
X
W
U
T
S
Q
P
N
L
K
J
G
F
E
C
B
A
46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2
47 45 43 41 39 37 35 33 31 29 27 25 23 21 19 17 15 13 11 9 7 5 3 1
Figure 3.20
Socket 8 (Pentium Pro) Pinout showing power pin locations.
VccS
VccP
Vss
Vcc5
Other
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Socket PGA-370
In January 1999, Intel introduced a new socket for P6 class processors. The new socket is called
PGA-370, because it has 370 pins and was designed for lower cost PGA (Pin Grid Array) versions
of the Celeron and Pentium III processors. PGA-370 is designed to directly compete in the lower
end system market along with the Super7 platform supported by AMD and Cyrix. PGA-370 brings
the low cost of a socketed design, with less expensive processors, mounting systems, heat sinks,
etc. to the high performance P6 line of processors.
Initially all the Celeron and Pentium III processors were made in SECC (Single Edge Contact
Cartridge) or SEPP (Single Edge Processor Package) formats. These are essentially circuit boards
containing the processor and separate L2 cache chips on a small board that plugs into the motherboard via Slot 1. This type of design was necessary when the L2 cache chips were made a part
of the processor, but were not directly integrated into the processor die. Intel did make a multidie chip package for the Pentium Pro, but this proved to be a very expensive way to package the
chip, And, a board with separate chips was cheaper, which is why the Pentium II looks different
from the Pentium Pro.
Starting with the Celeron 300A processor introduced in August 1998, Intel began combining the
L2 cache directly on the processor die; it was no longer in separate chips. With the cache fully
integrated into the die, there was no longer a need for a board-mounted processor. Because it
costs more to make a Slot 1 board or cartridge-type processor instead of a socketed type, Intel
moved back to the socket design to reduce the manufacturing cost—especially with the Celeron,
which competes on the low end with Socket 7 chips from AMD and Cyrix.
The Socket PGA-370 pinout is shown in Figure 3.21.
The Celeron is gradually being shifted over to PGA-370, although for a time both were available.
All Celeron processors at 333MHz and lower were only available in the Slot 1 version. Celeron
processors from 366MHz–433MHz were available in both Slot 1 and Socket PGA-370 versions; all
Celeron processors from 466MHz and up are only available in the PGA-370 version.
A motherboard with a Slot 1 can be designed to accept almost any Celeron, Pentium II, or
Pentium III processor. To use the newer 466MHz and faster Celerons, which are only available in
PGA-370 form, a low-cost adapter called a “slot-ket” has been made available by several manufacturers. This is essentially a Slot 1 board containing only a PGA-370 socket, which allows you to
use a PGA-370 processor in any Slot 1 board. A typical slot-ket adapter is shown in the “Celeron”
section, later in this chapter.
◊◊ See “Celeron,” p. 174.
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1
2
AN
4
VSS
AM
AL
3
VSS
VSS
AK
5
VSS
VCC
Microprocessor Types and Specifications
6
A12#
VCC
7
8
A16#
VSS
A15#
VSS
Page 86
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
A6#
VCC
A13#
A28#
Rsvd
VSS
A9#
A3#
Rsvd
VCC
Rsvd
A11#
Rsvd
BPRI#
VSS
Rsvd
VREF6
VCC
A7#
DEFER#
VSS
REQ4#
A14#
Rsvd
Rsvd
Rsvd
VCC
VSS
REQ3#
REQ0#
Rsvd
LOCK#
TRDY#
VCC
HITM#
VREF7
DRDY#
VSS
HIT#
Rsvd
BR0#
VCC
DBSY#
PWRGD
ADS#
VSS
THRMDN
RS2#
TRST#
VCC
THRMDP
Rsvd
TDI
TDO
VSS
TCK
TMS
VID0
VID2
VCC
A21#
AG
VSS
VSS
EDGCTRL
VCC
Rsvd
VSS
A10#
A19#
VCC
A5#
VSS
A8#
VCC
A4#
VSS
BNR#
VCC
REQ1#
VSS
REQ2#
VCC
Rsvd
VSS
RS1#
VCC
VCC
VSS
RS0#
VCC
THERMTRIP#
VSS
SLP#
BSEL#
VCC
VSS
SMI#
VID3
VSS
AE
AD
A17#
INIT#
Rsvd
Z
A27#
Y
X
IGNNE#
AG
FLUSH#
AE
STPCLK#
M
J
H
D
Rsvd
VCC
VSS
AA
Z
V2.5
VCC
D15#
D8#
D5#
D12#
D10#
VCC
D2#
D14#
D13#
VCC
VREF2
VSS
D26#
VREF3
VCC
D9#
VSS
D3#
VCC
D16#
VCC
VCC
D25#
VCC
VCC
VCC
VSS
VCC
D27#
VSS
VCC
VCC
D63#
VSS
VREF1
VCC
VSS
VSS
VCC
VCOREPET
VSS
Rsvd
VCC
D62#
VSS
Rsvd
VCC
Rsvd
VSS
Rsvd
M
LINT1
K
PREQ#
H
J
VCC
Rsvd
G
Rsvd
VCC
VREF0
L
VSS
PICD0
VSS
BP2#
Rsvd
Rsvd
LINT0
PICD1
VSS
B
D33#
VSS
VCC
D35#
D31#
VSS
D29#
1
2
VCC
3
D38#
D34#
VCC
D28#
4
Figure 3.21
5
D36#
VSS
D43#
6
D39#
7
D45#
VCC
D37#
8
D42#
D41#
D49#
VSS
D44#
D52#
D40#
VCC
D51#
VSS
D59#
VSS
D47#
VCC
D55#
VCC
D48#
VSS
D54#
VSS
D57#
VCC
D58#
VCC
D46#
VSS
D50#
VSS
D53#
VCC
D56#
VCC
D60#
VSS
Rsvd
VSS
D61#
VCC
VSS
BPM1#
Rsvd
VCC
Rsvd
VSS
Rsvd
VSS
Rsvd
VCC
Rsvd
BP3#
D
C
CPUPRES#
B
A
Rsvd
PRDY#
F
E
VCC
BPM0#
P
N
Rsvd
PICCLK
D22#
Rsvd
VSS
VSS
R
Q
Rsvd
Rsvd
D32#
Rsvd
VCC
VCC
T
S
Rsvd
Rsvd
D19#
Rsvd
VSS
VSS
V
U
Rsvd
Rsvd
VSS
VCC
VCC
X
W
BCLK
VSS
Rsvd
D24#
VSS
VSS
Rsvd
PLL2
VCC
D23#
VCC
VSS
VSS
D30#
D21#
D6#
VCC
D11#
D20#
D7#
VCC
VSS
D18#
VSS
VREF4
VCC
D17#
VCC
VCC
PLL1
VSS
D1#
Rsvd
VSS
C
A
AC
AB
VCMOS
Rsvd
VSS
Rsvd
Rsvd
VCC
E
VSS
Rsvd
D4#
G
F
VCC
VCC
AD
V1.5
FERR#
Rsvd
A18#
RESET#
VSS
L
K
VSS
VSS
AF
VSS
IERR#
VSS
VCC
A26#
D0#
Q
P
N
VCC
A23#
A29#
Rsvd
S
R
VREF5
A30#
Rsvd
U
T
A20M#
VSS
A24#
VCC
Y
W
V
A31#
VSS
VSS
VCC
A20#
VCC
AA
A25#
A22#
VSS
AC
AB
Rsvd
AJ
AH
VCC
AF
VCC
AL
AK
VSS
AJ
AH
AN
AM
VID1
VSS
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
Socket PGA-370 (PGA Celeron) pinout (top view).
Zero Insertion Force (ZIF) Sockets
When Intel created the Socket 1 specification, they realized that if users were going to upgrade
processors, they had to make the process easier. They found that it typically takes 100 pounds of
insertion force to install a chip in a standard 169-pin screw Socket 1 motherboard. With this
much force involved, you easily could damage either the chip or socket during removal or reinstallation. Because of this, some motherboard manufacturers began using Low Insertion Force
(LIF) sockets, which typically required only 60 pounds of insertion force for a 169-pin chip. With
the LIF or standard socket, I usually advise removing the motherboard—that way you can support the board from behind when you insert the chip. Pressing down on the motherboard with
60–100 pounds of force can crack the board if it is not supported properly. A special tool is also
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87
required to remove a chip from one of these sockets. As you can imagine, even the low insertion
force was relative, and a better solution was needed if the average person was going to ever
replace their CPU.
Manufacturers began inserting special Zero Insertion Force (ZIF) sockets in their later Socket 1
motherboard designs. Since then, virtually all processor sockets have been of the ZIF design.
Note, however, that a given Socket X specification has nothing to do with whether it is ZIF, LIF,
or standard; the socket specification covers only the pin arrangement. These days, nearly all
motherboard manufacturers are using ZIF sockets. These sockets almost eliminate the risk
involved in upgrading because no insertion force is necessary to install the chip. Most ZIF sockets
are handle-actuated; you lift the handle, drop the chip into the socket, and then close the handle. This design makes replacing the original processor with the upgrade processor an easy task.
Because of the number of pins involved, virtually all CPU sockets from Socket 2 through the present are implemented in ZIF form. This means that since the 486 era, removing the CPU from
most motherboards does not require any tools.
Processor Slots
After introducing the Pentium Pro with its integrated L2 cache, Intel discovered that the physical
package they chose was very costly to produce. They were looking for a way to easily integrate
cache and possibly other components into a processor package, and they came up with a cartridge or board design as the best way to do this. In order to accept their new cartridges, Intel
designed two different types of slots that could be used on motherboards.
Slot 1 is a 242-pin slot that is designed to accept Pentium II, Pentium III, and most Celeron
processors. Slot 2 is a more sophisticated 330-pin slot that is designed for the Pentium II and III
Xeon processors, which are primarily for workstations and servers. Besides the extra pins, the
biggest difference between Slot 1 and Slot 2 is the fact that Slot 2 was designed to host up to
four-way or more processing in a single board. Slot 1 only allows single or dual processing
functionality.
Note that Slot 2 is also called SC330, which stands for Slot Connector with 330 pins.
Slot 1
Slot 1 is used by the SEC (Single Edge Cartridge) design used with the Pentium II processors.
Inside the cartridge is a substrate card that includes the processor and L2 cache. Unlike the
Pentium Pro, the L2 cache is mounted on the circuit board and not within the same chip package
as the processor. This allows Intel to use aftermarket SRAM chips instead of making them internally, and also allows them to make Pentium II processors with different amounts of cache easily.
For example, the Celeron versions of the Pentium II have no L2 cache, whereas other future versions will have more than the standard 512KB included in most Pentium II processors. Figure
3.22 shows the Slot 1 connector dimensions and pin layout.
√√ See “Single Edge Cartridge (SEC) and Single Edge Processor (SEP),” p. 71.
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B74
B1
B141
B73
132.87±.25
5.231±.010
72.00
2.832
R 0.25
.010
2.54±.127
.100±.005
47.00
1.850
2.50
.098
73 CONTACT PAIRS
2.50
.098 48 CONTACT PAIRS
1.88±.10
.074±.004
9.50±.25
.374±.010
1.27
.050
4.75
.187
1.78±.03
.070±.001
2.00±.127
.079±.005
76.13 (MIN)
2.997 (MIN)
51.13 (MIN)
2.013 (MIN)
A1
A74
A141
A73
Figure 3.22
.94
.037
Slot 1 connector dimensions and pin layout.
Table 3.10 lists the names of each of the pins in the Slot 1 connector.
Table 3.10
Pin No.
Slot 1 Signal Listing in Order by Pin Number
Pin Name
Pin No.
Pin Name
Pin No.
Pin Name
A1
VCC_VTT
A25
DEP#[0]
A49
D#[37]
A2
GND
A26
GND
A50
GND
A3
VCC_VTT
A27
DEP#[1]
A51
D#[33]
A4
IERR#
A28
DEP#[3]
A52
D#[35]
A5
A20M#
A29
DEP#[5]
A53
D#[31]
A6
GND
A30
GND
A54
GND
A7
FERR#
A31
DEP#[6]
A55
D#[30]
A8
IGNNE#
A32
D#[61]
A56
D#[27]
A9
TDI
A33
D#[55]
A57
D#[24]
A10
GND
A34
GND
A58
GND
A11
TDO
A35
D#[60]
A59
D#[23]
A12
PWRGOOD
A36
D#[53]
A60
D#[21]
A13
TESTHI
A37
D#[57]
A61
D#[16]
A14
GND
A38
GND
A62
GND
A15
THERMTRIP#
A39
D#[46]
A63
D#[13]
A16
Reserved
A40
D#[49]
A64
D#[11]
A17
LINT[0]/INTR
A41
D#[51]
A65
D#[10]
A18
GND
A42
GND
A66
GND
A19
PICD[0]
A43
D#[42]
A67
D#[14]
A20
PREQ#
A44
D#[45]
A68
D#[9]
A21
BP#[3]
A45
D#[39]
A69
D#[8]
A22
GND
A46
GND
A70
GND
A23
BPM#[0]
A47
Reserved
A71
D#[5]
A24
BINIT#
A48
D#[43]
A72
D#[3]
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Chapter 3
Pin No.
Pin Name
Pin No.
Pin Name
Pin No.
Pin Name
A73
D#[1]
A113
Reserved
B32
D#[63]
A74
GND
A114
GND
B33
VCC_CORE
A75
BCLK
A115
ADS#
B34
D#[56]
A76
BR0#
A116
Reserved
B35
D#[50]
A77
BERR#
A117
AP#[0]
B36
D#[54]
A78
GND
A118
GND
B37
VCC_CORE
A79
A#[33]
A119
VID[2]
B38
D#[59]
A80
A#[34]
A120
VID[1]
B39
D#[48]
A81
A#[30]
A121
VID[4]
B40
D#[52]
A82
GND
B1
EMI
B41
EMI
A83
A#[31]
B2
FLUSH#
B42
D#[41]
A84
A#[27]
B3
SMI#
B43
D#[47]
A85
A#[22]
B4
INIT#
B44
D#[44]
A86
GND
B5
VCC_VTT
B45
VCC_CORE
A87
A#[23]
B6
STPCLK#
B46
D#[36]
A88
Reserved
B7
TCK
B47
D#[40]
A89
A#[19]
B8
SLP#
B48
D#[34]
A90
GND
B9
VCC_VTT
B49
VCC_CORE
A91
A#[18]
B10
TMS
B50
D#[38]
A92
A#[16]
B11
TRST#
B51
D#[32]
A93
A#[13]
B12
Reserved
B52
D#[28]
A94
GND
B13
VCC_CORE
B53
VCC_CORE
A95
A#[14]
B14
Reserved
B54
D#[29]
A96
A#[10]
B15
Reserved
B55
D#[26]
A97
A#[5]
B16
LINT[1]/NMI
B56
D#[25]
A98
GND
B17
VCC_CORE
B57
VCC_CORE
A99
A#[9]
B18
PICCLK
B58
D#[22]
A100
A#[4]
B19
BP#[2]
B59
D#[19]
A101
BNR#
B20
Reserved
B60
D#[18]
A102
GND
B21
BSEL#
B61
EMI
A103
BPRI#
B22
PICD[1]
B62
D#[20]
A104
TRDY#
B23
PRDY#
B63
D#[17]
A105
DEFER#
B24
BPM#[1]
B64
D#[15]
A106
GND
B25
VCC_CORE
B65
VCC_CORE
A107
REQ#[2]
B26
DEP#[2]
B66
D#[12]
A108
REQ#[3]
B27
DEP#[4]
B67
D#[7]
A109
HITM#
B28
DEP#[7]
B68
D#[6]
A110
GND
B29
VCC_CORE
B69
VCC_CORE
A111
DBSY#
B30
D#[62]
B70
D#[4]
A112
RS#[1]
B31
D#[58]
B71
D#[2]
(continues)
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Table 3.10
Page 90
Microprocessor Types and Specifications
Continued
Pin No.
Pin Name
Pin No.
Pin Name
Pin No.
Pin Name
B72
D#[0]
B89
VCC_CORE
B106
LOCK#
B73
VCC_CORE
B90
A#[15]
B107
DRDY#
B74
RESET#
B91
A#[17]
B108
RS#[0]
B75
BR1#
B92
A#[11]
B109
VCC5
B76
FRCERR
B93
VCC_CORE
B110
HIT#
B77
VCC_CORE
B94
A#[12]
B111
RS#[2]
B78
A#[35]
B95
A#[8]
B112
Reserved
B79
A#[32]
B96
A#[7]
B113
VCC_L2
B80
A#[29]
B97
VCC_CORE
B114
RP#
B81
EMI
B98
A#[3]
B115
RSP#
B82
A#[26]
B99
A#[6]
B116
AP#[1]
B83
A#[24]
B100
EMI
B117
VCC_L2
B84
A#[28]
B101
SLOTOCC#
B118
AERR#
B85
VCC_CORE
B102
REQ#[0]
B119
VID[3]
B86
A#[20]
B103
REQ#[1]
B120
VID[0]
B87
A#[21]
B104
REQ#[4]
B121
VCC_L2
B88
A#[25]
B105
VCC_CORE
Slot 2 (SC330)
Slot 2 (otherwise called SC330) is used on high-end motherboards that support the Pentium II
and III Xeon processors. Figure 3.23 shows the Slot 2 connector.
Pin B1
Pin B2
Pin A2
Pin A1
Top View
Pin B165
Pin A166
Side View
Figure 3.23
Slot 2 (SC330) connector dimensions and pin layout.
The Pentium II or III is designed in a cartridge similar to, but larger than, that used for the
Pentium II. Figure 3.24 shows the Xeon cartridge.
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CPU Operating Voltages
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91
Plastic Enclosure
Primary Side Substrate
Processor and Cache
Thermal Plate Retention Clips
Pin Fasteners
Aluminum Thermal Plate
Figure 3.24
Pentium II/III Xeon cartridge.
Motherboards featuring Slot 2 are primarily found in higher end systems such as workstations or
servers, which use the Pentium II or III Xeon processors. These are Intel’s high-end chips, which
differ from the standard Pentium II/III mainly by virtue of having full core-speed L2 cache, and
more of it.
CPU Operating Voltages
One trend that is clear to anybody that has been following processor design is that the operating
voltages have gotten lower and lower. The benefits of lower voltage are threefold. The most obvious is that with lower voltage comes lower overall power consumption. By consuming less power,
the system will be less expensive to run, but more importantly for portable or mobile systems, it
will run much longer on existing battery technology. The emphasis on battery operation has driven many of the advances in lowering processor voltage, because this has a great effect on battery
life.
The second major benefit is that with less voltage and therefore less power consumption, there
will be less heat produced. Processors that run cooler can be packed into systems more tightly
and will last longer. The third major benefit is that a processor running cooler on less power can
be made to run faster. Lowering the voltage has been one of the key factors in allowing the clock
rates of processors to go higher and higher.
Until the release of the mobile Pentium and both desktop and mobile Pentium MMX, most
processors used a single voltage level to power both the core as well as run the input/output circuits. Originally, most processors ran both the core and I/O circuits at 5 volts, which was later
was reduced to 3.5 or 3.3 volts to lower power consumption. When a single voltage is used for
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Microprocessor Types and Specifications
both the internal processor core power as well as the external processor bus and I/O signals, the
processor is said to have a single or unified power plane design.
When originally designing a version of the Pentium processor for mobile or portable computers,
Intel came up with a scheme to dramatically reduce the power consumption while still remaining
compatible with the existing 3.3v chipsets, bus logic, memory, and other components. The result
was a dual-plane or split-plane power design where the processor core ran off of a lower voltage
while the I/O circuits remained at 3.3v. This was originally called Voltage Reduction Technology
(VRT) and first debuted in the Mobile Pentium processors released in 1996. Later, this dual-plane
power design also appeared in desktop processors such as the Pentium MMX, which used 2.8v to
power the core and 3.3v for the I/O circuits. Now most recent processors, whether for mobile or
desktop use, feature a dual-plane power design. Some of the more recent Mobile Pentium II
processors run on as little as 1.6v for the core while still maintaining compatibility with 3.3v
components for I/O.
Knowing the processor voltage requirements is not a big issue with Pentium Pro (Socket 8) or
Pentium II (Slot 1 or Slot 2) processors, because these sockets and slots have special voltage ID
(VID) pins that the processor uses to signal to the motherboard the exact voltage requirements.
This allows the voltage regulators built in to the motherboard to be automatically set to the correct voltage levels by merely installing the processor.
Unfortunately, this automatic voltage setting feature is not available on Socket 7 and earlier
motherboard and processor designs. This means you must normally set jumpers or otherwise
configure the motherboard according to the voltage requirements of the processor you are
installing. Pentium (Socket 4, 5, or 7) processors have run on a number of voltages, but the latest
MMX versions are all 2.8v, except for mobile Pentium processors, which are as low as 1.8v. Table
3.11 lists the voltage settings used by Intel Pentium (non-MMX) processors that use a single
power plane. This means that both the CPU core and the I/O pins run at the same voltage.
Table 3.11 shows voltages used by Socket 7 processors.
Table 3.11
Socket 7 Single- and Dual-Plane Processor Voltages
Voltage
Setting
Processor
Core
Voltage
I/O
Voltage
Voltage
Planes
VRE (3.5v)
STD (3.3v)
MMX (2.8v)
VRE (3.5v)
3.2v
2.9v
2.4v
2.2v
VRE (3.5v)
2.9v
MMX (2.8v)
2.45v
Intel Pentium
Intel Pentium
Intel MMX Pentium
AMD K5
AMD-K6
AMD-K6
AMD-K6-2/K6-3
AMD-K6/K6-2
Cyrix 6x86
Cyrix 6x86MX/M-II
Cyrix 6x86L
Cyrix 6x86LV
3.5v
3.3v
2.8v
3.5v
3.2v
2.9v
2.4v
2.2v
3.5v
2.9v
2.8v
2.45v
3.5v
3.3v
3.3v
3.5v
3.3v
3.3v
3.3v
3.3v
3.5v
3.3v
3.3v
3.3v
Single
Single
Dual
Single
Dual
Dual
Dual
Dual
Single
Dual
Dual
Dual
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Normally, the acceptable range is plus or minus five percent from the nominal intended setting.
Most Socket 7 and later Pentium motherboards supply several voltages (such as 2.5v, 2.7v, 2.8v,
and 2.9v) for compatibility with future devices. A voltage regulator built into the motherboard
converts the power supply voltage into the different levels required by the processor core. Check
the documentation for your motherboard and processor to find the appropriate settings.
The Pentium Pro and Pentium II processors automatically determine their voltage settings by
controlling the motherboard-based voltage regulator through built-in voltage ID (VID) pins.
Those are explained in more detail later in this chapter.
◊◊ See “Pentium Pro Processors,” p. 156.
◊◊ See “Pentium II Processors,” p. 162.
Note that on the STD or VRE settings, the core and I/O voltages are the same; these are single
plane voltage settings. Anytime a different voltage other than STD or VRE is set, the motherboard
defaults to a dual-plane voltage setting where the core voltage can be specifically set, while the
I/O voltage remains constant at 3.3v no matter what.
Socket 5 was only designed to supply STD or VRE settings, so any processor that can work at
those settings can work in Socket 5 as well as Socket 7. Older Socket 4 designs can only supply 5v,
plus they have a completely different pinout (fewer pins overall), so it is not possible to use a
processor designed for Socket 7 or Socket 5 in Socket 4.
Most Socket 7 and later Pentium motherboards supply several voltages (such as 2.2v, 2.4v, 2.5v,
2.7v, 2.8v, and 2.9v as well as the older STD or VRE settings) for compatibility with many processors. A voltage regulator built into the motherboard converts the power supply voltage into the
different levels required by the processor core. Check the documentation for your motherboard
and processor to find the appropriate settings.
The Pentium Pro, Celeron, and Pentium II/III processors automatically determine their voltage
settings by controlling the motherboard-based voltage regulator. That’s done through built-in
voltage ID (VID) pins.
For hot rodding purposes, many newer motherboards for these processors have override settings
that allow for manual voltage adjustment if desired. Many people have found that when attempting to overclock a processor, it often helps to increase the voltage by a tenth of a volt or so. Of
course this increases the heat output of the processor and must be accounted for with adequate
heat sinking.
Heat and Cooling Problems
Heat can be a problem in any high-performance system. The higher speed processors normally
consume more power and therefore generate more heat. The processor is usually the single most
power-hungry chip in a system, and in most situations, the fan inside your computer case might
not be capable of handling the load without some help.
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Heat Sinks
To cool a system in which processor heat is a problem, you can buy (for less than $5, in most
cases) a special attachment for the CPU chip called a heat sink, which draws heat away from the
CPU chip. Many applications may need only a larger standard heat sink with additional or longer
fins for a larger cooling area. Several heat-sink manufacturers are listed in the Vendor List, on
the CD.
A heat sink works like the radiator in your car, pulling heat away from the engine. In a similar
fashion, the heat sink conducts heat away from the processor so that it can be vented out of the
system. It does this by using a thermal conductor (usually metal) to carry heat away from the
processor into fins that expose a high amount of surface area to moving air. This allows the air to
be heated, thus cooling the heat sink and the processor as well. Just like the radiator in your car,
the heat sink depends on airflow. With no moving air, a heat sink is incapable of radiating the
heat away. To keep the engine in your car from overheating when the car is not moving, auto
engineers incorporate a fan. Likewise, there is always a fan somewhere inside your PC helping to
move air across the heat sink and vent it out of the system. Sometimes the fan included in the
power supply is enough, other times an additional fan must be added to the case, or even directly
over the processor to provide the necessary levels of cooling.
The heat sink is clipped or glued to the processor. A variety of heat sinks and attachment methods exist. Figure 3.25 shows various passive heat sinks and attachment methods.
Clips to Processor
LIF Style
Bond-on Style
ZIF Style
Figure 3.25
Passive heat sinks for socketed processors showing various attachment methods.
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Tip
According to data from Intel, heat sink clips are the number two destroyer of motherboards (screwdrivers are number one). When installing or removing a heat sink that is clipped on, make sure you don’t scrape the surface of the
motherboard. In most cases, the clips hook over protrusions in the socket, and when installing or removing the
clips, it is very easy to scratch or scrape the surface of the board right below where the clip ends attach. I like to
place a thin sheet of plastic underneath the edge of the clip while I work, especially if there are board traces that
can be scratched in the vicinity.
Heat sinks are rated for their cooling performance. Typically the ratings are expressed as a resistance to heat transfer, in degrees centigrade per watt (°C/W), where lower is better. Note that the
resistance will vary according to the airflow across the heat sink. To ensure a constant flow of air
and more consistent performance, many heat sinks incorporate fans so they don’t have to rely on
the airflow within the system. Heat sinks with fans are referred to as active heat sinks (see Figure
3.26). Active heat sinks have a power connection, often using a spare disk drive power connector,
although most newer motherboards now have dedicated heat sink power connections right on
the board.
Figure 3.26
Active heat sinks for socketed processors.
Active heat sinks use a fan or other electric cooling device, which require power to run. The fan
type is most common but some use a peltier cooling device, which is basically a solid-state refrigerator. Active heat sinks require power and normally plug into a disk drive power connector or
special 12v fan power connectors on the motherboard. If you do get a fan type heat sink, be
aware that some on the market are very poor quality. The bad ones have motors that use sleeve
bearings, which freeze up after a very short life. I only recommend fans with ball-bearing motors,
which will last about 10 times longer than the sleeve-bearing types. Of course, they cost more,
but only about twice as much, which means you’ll save money in the long run.
Figure 3.27 shows an active heat sink arrangement on a Pentium II/III type processor. This is
common on what Intel calls their “boxed processors,” which are sold individually and through
dealers.
The passive heat sinks are 100 percent reliable, as they have no mechanical components to fail.
Passive heat sinks (see Figure 3.28) are basically an aluminum-finned radiator that dissipates heat
through convection. Passive types don’t work well unless there is some airflow across the fins,
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normally provided by the power supply fan or an extra fan in the case. If your case or power supply is properly designed, you can use a less expensive passive heat sink instead of an active one.
Processor
Fan
Shroud Covering
Heatsink Fans
Heatsink
Support
Retention
Mechanism
Fan Power
Connector
Figure 3.27
processors.
Motherboard
An active (fan powered) heat sink and supports used with Pentium II/III type
S.E.C. Cartridge with
Heatsink Attached
Retention Mechanism
Heatsink
Support Base
Slot 1 Connector
Heatsink Support
Top Bar
Retention Mechanism
Attach Mounts
Figure 3.28
A passive heat sink and supports used with Pentium II/III type processors.
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Tip
To function effectively, a heat sink must be as directly attached to the processor as possible. To eliminate air gaps
and ensure a good transfer of heat, in most cases, you should put a thin coating of thermal transfer grease on the
surface of the processor where the heat sink attaches. This will dramatically decrease the thermal resistance properties and is required for maximum performance.
In order to have the best possible transfer of heat from the processor to the heat sink, most heat
sink manufacturers specify some type of thermal interface material to be placed between the
processor and the heat sink. This normally consists of a zinc-based white grease (similar to what
skiers put on their noses to block the sun), but can also be a special pad or even a type of doublestick tape. Using a thermal interface aid such as thermal grease can improve heat sink performance dramatically. Figure 3.29 shows the thermal interface pad or grease positioned between
the processor and heat sink.
Thin Lid
Heat Sink
Thermal Interface Material
Ceramic substrate
Heat Sink Clip
Die
ZIF Socket
Motherboard
Figure 3.29
Thermal interface material helps transfer heat from the processor die to the heat sink.
Most of the newer systems on the market use an improved motherboard form factor (shape)
design called ATX. Systems made from this type of motherboard and case allow for improved
cooling of the processor due to the processor being repositioned in the case near the power supply. Also, most of these cases now feature a secondary fan to further assist in cooling. Normally
the larger case mounted fans are more reliable than the smaller fans included in active heat sinks.
A properly designed case can move sufficient air across the processor, allowing for a more reliable
and less expensive passive (no fan) heat sink to be used.
◊◊ See “ATX,” p. 214.
Math Coprocessors (Floating-Point Units)
This section covers the floating-point unit (FPU) contained in the processor, which was formerly a
separate external math coprocessor in the 386 and older chips. Older central processing units
designed by Intel (and cloned by other companies) used an external math coprocessor chip.
However, when Intel introduced the 486DX, they included a built-in math coprocessor, and every
processor built by Intel (and AMD and Cyrix, for that matter) since then includes a math coprocessor. Coprocessors provide hardware for floating-point math, which otherwise would create an
excessive drain on the main CPU. Math chips speed your computer’s operation only when you are
running software designed to take advantage of the coprocessor. All the subsequent fifth and sixth
generation Intel and compatible processors (such as those from AMD and Cyrix) have featured an
integrated floating-point unit, although the Intel ones are known for having the best performance.
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Math chips (as coprocessors sometimes are called) can perform high-level mathematical operations—long division, trigonometric functions, roots, and logarithms, for example, at 10 to 100
times the speed of the corresponding main processor. The operations performed by the math chip
are all operations that make use of noninteger numbers (numbers that contain digits after the
decimal point). The need to process numbers in which the decimal is not always the last character leads to the term floating point because the decimal (point) can move (float), depending on the
operation. The integer units in the primary CPU work with integer numbers, so they perform
addition, subtraction, and multiplication operations. The primary CPU is designed to handle
such computations; these operations are not offloaded to the math chip.
The instruction set of the math chip is different from that of the primary CPU. A program must
detect the existence of the coprocessor, and then execute instructions written explicitly for that
coprocessor; otherwise, the math coprocessor draws power and does nothing else. Fortunately,
most modern programs that can benefit from the use of the coprocessor correctly detect and use
the coprocessor. These programs usually are math-intensive: spreadsheet programs, database
applications, statistical programs, and graphics programs, such as computer-aided design (CAD)
software. Word processing programs do not benefit from a math chip and therefore are not
designed to use one. Table 3.12 summarizes the coprocessors available for the Intel family of
processors.
Table 3.12 matches processors and the coprocessor it uses.
Table 3.12
Math Coprocessor Summary
Processor
Coprocessor
8086
8087
8088
8087
286
287
386SX
387SX
386DX
387DX
486SX
487SX, DX2/OverDrive*
487SX*
Built-in FPU
486SX2
DX2/OverDrive**
486DX
Built-in FPU
486DX2
Built-in FPU
486DX4/5x86
Built-in FPU
Intel Pentium/Pentium MMX
Built-in FPU
Cyrix 6x86/MI/MII
Built-in FPU
AMD K5/K6
Built-in FPU
Pentium II/III/Celeron/Xeon
Built-in FPU
FPU = Floating-point unit
*The 487SX chip is a modified pinout 486DX chip with the math coprocessor enabled. When you plug in a
487SX chip, it disables the 486SX main processor and takes over all processing.
**The DX2/OverDrive is equivalent to the SX2 with the addition of a functional FPU.
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Although virtually all processors since the 486 series have built-in floating-point units, they vary
in performance. Historically the Intel processor FPUs have dramatically outperformed those from
AMD and Cyrix, although AMD and Cyrix are achieving performance parity in their newer offerings.
Within each of the original 8087 group, the maximum speed of the math chips varies. A suffix
digit after the main number, as shown in Table 3.13, indicates the maximum speed at which a
system can run a math chip.
Table 3.13
Maximum Math Chip Speeds
Part
Speed
Part
Speed
8087
5MHz
287
6MHz
8087-3
5MHz
287-6
6MHz
8087-2
8MHz
287-8
8MHz
8087-1
10MHz
287-10
10MHz
The 387 math coprocessors, and the 486 or 487 and Pentium processors, always indicate their
maximum speed rating in MHz in the part number suffix. A 486DX2-66, for example, is rated to
run at 66MHz. Some processors incorporate clock multiplication, which means that they can run
at different speeds compared with the rest of the system.
Tip
The performance increase in programs that use the math chip can be dramatic—usually, a geometric increase in
speed occurs. If the primary applications that you use can take advantage of a math coprocessor, you should
upgrade your system to include one.
Most systems that use the 386 or earlier processors are socketed for a math coprocessor as an
option, but they do not include a coprocessor as standard equipment. A few systems on the market don’t even have a socket for the coprocessor because of cost and size considerations. These
systems are usually low cost or portable systems, such as older laptops, the IBM PS/1, and the
PCjr. For more specific information about math coprocessors, see the discussions of the specific
chips—8087, 287, 387, and 487SX—in the later sections. Table 3.14 shows the specifications of
the various math coprocessors.
Table 3.14
Older Intel Math Coprocessor Specifications
Name
Power
Consumption
Case Minimum
Temperature
Case Maximum
Temperature
No. of
Transistors
Date
Introduced
8087
3 watts
0°C, 32°F
85°C, 185°F
45,000
1980
287
3 watts
0°C, 32°F
85°C, 185°F
45,000
1982
287XL
1.5 watts
0°C, 32°F
85°C, 185°F
40,000
1990
387SX
1.5 watts
0°C, 32°F
85°C, 185°F
120,000
1988
387DX
1.5 watts
0°C, 32°F
85°C, 185°F
120,000
1987
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Most often, you can learn what CPU and math coprocessor are installed in a particular system by
checking the markings on the chip.
Processor Bugs
Processor manufacturers use specialized equipment to test their own processors, but you have to
settle for a little less. The best processor-testing device to which you have access is a system that
you know is functional; you then can use the diagnostics available from various utility software
companies or your system manufacturer to test the motherboard and processor functions.
Companies such as Diagsoft, Symantec, Micro 2000, Trinitech, Data Depot, and others offer specialized diagnostics software that can test the system, including the processor. If you don’t want
to purchase this kind of software, you can perform a quick-and-dirty processor evaluation by
using the diagnostics program supplied with your system.
Perhaps the most infamous of these is the floating-point division math bug in the early Pentium
processors. This and a few other bugs are discussed in detail later in this chapter.
Because the processor is the brain of a system, most systems don’t function with a defective
processor. If a system seems to have a dead motherboard, try replacing the processor with one
from a functioning motherboard that uses the same CPU chip. You might find that the processor
in the original board is the culprit. If the system continues to play dead, however, the problem is
elsewhere, most likely in the motherboard, memory, or power supply. See the chapters that cover
those parts of the system for more information on troubleshooting those components. I must say
that in all my years of troubleshooting and repairing PCs, I have rarely encountered defective
processors.
A few system problems are built in at the factory, although these bugs or design defects are rare.
By learning to recognize these problems, you can avoid unnecessary repairs or replacements. Each
processor section describes several known defects in that generation of processors, such as the
infamous floating-point error in the Pentium. For more information on these bugs and defects,
see the following sections, and check with the processor manufacturer for updates.
Processor Update Feature
All processors can contain design defects or errors. Many times, the effects of any given bug can
be avoided by implementing hardware or software workarounds. Intel documents these bugs and
workarounds well for their processors in their processor Specification Update manuals; this manual is available from their Web site. Most of the other processor manufacturers also have bulletins
or tips on their Web sites listing any problems or special fixes or patches for their chips.
Previously, the only way to fix a processor bug was to work around it or replace the chip with
one that had the bug fixed. Now, a new feature built into the Intel P6 processors, including the
Pentium Pro and Pentium II, can allow many bugs to be fixed by altering the microcode in the
processor. Microcode is essentially a set of instructions and tables in the processor that control
how the processor operates. These processors incorporate a new feature called reprogrammable
microcode, which allows certain types of bugs to be worked around via microcode updates. The
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microcode updates reside in the system ROM BIOS and are loaded into the processor by the system BIOS during the power on self test (POST). Each time the system is rebooted, the fix code is
reloaded, ensuring that it will have the bug fix installed anytime the processor is operating.
The easiest method for checking the microcode update is to use the Pentium Pro and Pentium II
processor update utility, which is developed and supplied by Intel. This utility can verify whether
the correct update is present for all Pentium Pro processor-based motherboards. The utility displays the processor stepping and version of the microcode update. A stepping is the processor
hardware equivalent of a new version. In software, we refer to minor version changes as 1.0, 1.1,
1.2, etc., while in processors we call these minor revisions steppings.
To install a new microcode update, however, the motherboard BIOS must contain the routines to
support the microcode update, which virtually all Pentium Pro and Pentium II BIOSes do have.
The Intel processor update utility determines whether the code is present in the BIOS, compares
the processor stepping with the microcode update currently loaded, and installs the new update,
if needed. Use of this utility with motherboards containing the BIOS microcode update routine
allows just the microcode update data to be changed; the rest of the BIOS is unchanged. A version of the update utility is provided with all Intel boxed processors. The term boxed processors
refers to processors packaged for use by system integrators, that is, people who build systems. If
you want the most current version of this utility, you have to contact an Intel processor dealer to
download it, because Intel only supplies it to their dealers.
Note that if the BIOS in your motherboard does not include the processor microcode update routine, you should get a complete system BIOS upgrade from the motherboard vendor.
When you are building a system with a Pentium Pro, Celeron, or Pentium II/III processor, you
must use the processor update utility to check that the system BIOS contains microcode updates
that are specific to particular silicon stepping of the processor you are installing. In other words,
you must ensure that the update matches the processor stepping being used.
Table 3.15 contains the current microcode update revision for each processor stepping. These
update revisions are contained in the microcode update database file that comes with the
Pentium Pro processor and Pentium II processor update utility. Processor steppings are listed in
the sections on the Pentium, Pentium Pro, and Pentium II processors later in this chapter.
Table 3.15 Processor Steppings (Revisions) and Microcode Update Revisions
Supported by the Update Database File PEP6.PDB
Processor
Stepping
Stepping
Signature
Microcode Update
Revision Required
Pentium Pro
C0
0x612
0xC6
Pentium Pro
sA0
0x616
0xC6
Pentium Pro
sA1
0x617
0xC6
Pentium Pro
sB1
0x619
0xD1
Pentium II
C0
0x633
0x32
Pentium II
C1
0x634
0x33
Pentium II
dA0
0x650
0x15
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Using the processor update utility (CHECKUP3.EXE) available from Intel, a system builder can
easily verify that the correct microcode update is present in all systems based on the P6 (Pentium
Pro, Celeron, Pentium II/III and Xeon) processors. For example, if a system contains a processor
with stepping C1 and stepping signature 0x634, the BIOS should contain the microcode update
revision 0x33. The processor update utility identifies the processor stepping, signature, and
microcode update revision that is currently in use.
If a new microcode update needs to be installed in the system BIOS, the system BIOS must contain the Intel-defined processor update routines so the processor update utility can permanently
install the latest update. Otherwise, a complete system BIOS upgrade is required from the motherboard manufacturer. It is recommended that the processor update utility be run after upgrading a
motherboard BIOS and before installing the operating system when building a system based on
any P6 processor. The utility is easy to use and executes in just a few seconds. Because the update
utility may need to load new code into your BIOS, ensure that any jumper settings on the motherboard are placed in the “enable flash upgrade” position. This enables writing to the flash
memory.
After running the utility, turn off power to the system and reboot—do not warm boot—to ensure
that the new update is correctly initialized in the processor. Also ensure that all jumpers, such as
any flash upgrade jumpers and so on, are returned to their normal position.
Intel Processor Codenames
Intel has always used codenames when talking about future processors. The codenames are normally not supposed to become public, but often they do. They can often be found in magazine
articles talking about future generation processors. Sometimes, they even appear in motherboard
manuals because the manuals are written before the processors are officially introduced. Table
3.16 lists Intel processor codenames for reference.
Table 3.16
Intel Processors and Codenames
Codename
Processor
P4
486DX
P4S
486SX
P23
486SX
P23S
487SX
P23N
487SX
P23T
486 OverDrive for the 80486 (169-pin PGA)
P4T
486 OverDrive for the 486 (168-pin PGA)
P24
486DX2
P24S
486DX2
P24D
486DX2WB (Write Back)
P24C
486DX4
P24CT
486DX4WB (Write Back)
P5
Pentium 60 or 66MHz, Socket 4, 5v
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Codename
Processor
P24T
486 Pentium OverDrive, 63 or 83MHz, Socket 3
P54C
Classic Pentium 75–200MHz, Socket 5/7, 3.3v
P55C
Pentium MMX 166–266MHz, Socket 7, 2.8v
P54CTB
Pentium MMX OverDrive 125+, Socket 5/7, 3.3v
Tillamook
Mobile Pentium MMX 0.25 micron, 166–266MHz, 1.8v
P6
Pentium Pro, Socket 8
Klamath
Original Pentium II, 0.35 micron, Slot 1
Deschutes
Pentium II, 0.25 micron, Slot 1 or 2
Covington
Celeron, PII w/ no L2 cache
Mendocino
Celeron, PII w/ 128KB L2 cache on die
Dixon
Pentium IIPE (mobile), 256KB on-die L2 cache
Katmai
Pentium III, PII w/ SSE instructions
Willamette
Pentium III w/ on-die L2
Tanner
Pentium III Xeon
Cascades
PIII, 0.18 micron, on-die L2
Chapter 3
Merced
P7, First IA-64 processor, on-die L2, 0.18 micron
McKinley
1GHz, Improved Merced, IA-64, 0.18 micron w/ copper interconnects
Foster
Improved PIII, IA-32
Madison
Improved McKinley, IA-64, 0.13 micron
103
Intel-Compatible Processors (AMD and Cyrix)
Severalcompanies—mainly AMD and Cyrix—have developed processors that are compatible with
Intel processors. These chips are fully Intel-compatible, so they emulate every processor instruction in the Intel chips. Most of the chips are pin-compatible, which means that they can be used
in any system designed to accept an Intel processor; others require a custom motherboard design.
Any hardware or software that works on Intel-based PCs will work on PCs made with these thirdparty CPU chips. A number of companies currently offer Intel-compatible chips, and I will discuss
some of the most popular ones here.
AMD Processors
Advanced Micro Devices (AMD) has become a major player in the Pentium-compatible chip market with their own line of Intel-compatible processors. AMD ran into trouble with Intel several
years ago because their 486-clone chips used actual Intel microcode. These differences have been
settled and AMD now has a five-year cross-license agreement with Intel. In 1996, AMD finalized a
deal to absorb NexGen, another maker of Intel-compatible CPUs. NexGen had been working on a
chip they called the Nx686, which was renamed the K6 and introduced by AMD. Since then,
AMD has refined the design as the K6-2 and K6-3. Their new chip, called the K7, is designed similarly to the Pentium II and III, and uses the same cartridge design. AMD currently offers a wide
variety of CPUs, from 486 upgrades to the K6 series and the new K7. Table 3.17 lists the basic
processors offered by AMD and their Intel socket.
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AMD CPU Summary
AMD CPU Type
P-Rating
Actual CPU
Speed (MHz)
Clock
Multiplier
Motherboard
Speed (MHz)
Socket
Am486DX4-100
n/a
100
3x
33
Socket 1,2,3
Am486DX4-120
n/a
120
3x
40
Socket 1,2,3
Am5x86-133
75
133
4x
33
Socket 1,2,3
K5
PR75
75
1.5x
50
Socket 5,7
K5
PR90
90
1.5x
60
Socket 5,7
K5
PR100
100
1.5x
66
Socket 5,7
K5
PR120
90
1.5x
60
Socket 5,7
K5
PR133
100
1.5x
66
Socket 5,7
K5
PR166
116.7
1.75x
66
Socket 5,7
K6
PR166
166
2.5x
66
Socket 7
K6
PR200
200
3x
66
Socket 7
K6
PR233
233
3.5x
66
Socket 7
K6
PR266
266
4x
66
Socket 7
K6
PR300
300
4.5x
66
Socket 7
K6-2
PR233
233
3.5x
66
Socket 7
K6-2
PR266
266
4x
66
Socket 7
K6-2
PR300
300
4.5x
66
Socket 7
K6-2
PR300
300
3x
100
Super7
K6-2
PR333
333
5x
66
Socket 7
K6-2
PR333
333
3.5x
95
Super7
K6-2
PR350
350
3.5x
100
Super7
K6-2
PR366
366
5.5x
66
Socket 7
K6-2
PR380
380
4x
95
Super7
K6-2
PR400
400
4x
100
Super7
K6-2
PR450
450
4.5x
100
Super7
K6-2
PR475
475
5x
95
Super7
K6-3
PR400
400
4x
100
Super7
K6-3
PR450
450
4.5x
100
Super7
Notice in the table that for the K5 PR120 through PR166 the model designation does not match the CPU clock
speed. This is called a PR rating instead and is further described earlier in this chapter.
Starting with the K6, the P-Rating equals the true MHz clock speed.
The model designations are meant to represent performance comparable with an equivalent Pentium-based system. AMD chips, particularly the new K6, have typically fared well in performance comparisons and usually
have a much lower cost. There is more information on the respective AMD chips in the sections for each different type of processor.
As you can see from the table, most of AMD’s newer processors are designed to use the Super7
interface they pioneered with Cyrix. Super7 is an extension to the standard Socket 7 design,
allowing for increased board speeds of up to 100MHz.
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Chapter 3
Cyrix
Cyrix has become an even larger player in the market since being purchased by National
Semiconductor in November 1997. Prior to that they had been a fabless company, meaning they
had no chip-manufacturing capability. All the Cyrix chips were manufactured for Cyrix first by
Texas Instruments, and then mainly IBM up through the end of 1998. Starting in 1999, National
Semiconductor has taken over manufacturing of the Cyrix processors. More recently, National
has been looking to sell the Cyrix division, as the PC business has not been what they thought it
would be. For now the future of Cyrix is a little unclear.
Like Intel, Cyrix has begun to limit its selection of available CPUs to only the latest technology.
Cyrix is currently focusing on the Pentium market with the M1 (6x86) and M2 (6x86MX) processors. The 6x86 has dual internal pipelines and a single, unified 16KB internal cache. It offers speculative and out-of-order instruction execution, much like the Intel Pentium Pro processor. The
6x86MX adds MMX technology to the CPU. The chip is Socket 7 compatible, but some require
modified chipsets and new motherboard designs. Table 3.18 lists Cyrix M1 processors and bus
speeds.
Table 3.18
Cyrix Processor Ratings Versus Actual Speeds
Cyrix CPU Type
P-Rating
Actual CPU
Speed (MHz)
Clock
Multiplier
Motherboard
Speed (MHz)
Socket
6x86
PR90
80
2x
40
Socket 5,7
6x86
PR120
100
2x
50
Socket 5,7
6x86
PR133
110
2x
55
Socket 5,7
6x86
PR150
120
2x
60
Socket 5,7
6x86
PR166
133
2x
66
Socket 5,7
6x86
PR200
150
2x
75
Super7
6x86MX
PR133
100
2x
50
Socket 7
6x86MX
PR133
110
2x
55
Socket 7
6x86MX
PR150
120
2x
60
Socket 7
6x86MX
PR150
125
2.5x
50
Socket 7
6x86MX
PR166
133
2x
66
Socket 7
6x86MX
PR166
137.5
2.5x
55
Socket 7
6x86MX
PR166
150
3x
50
Socket 7
6x86MX
PR166
150
2.5x
60
Socket 7
6x86MX
PR200
150
2x
75
Super7
6x86MX
PR200
165
3x
55
Socket 7
6x86MX
PR200
166
2.5x
66
Socket 7
6x86MX
PR200
180
3x
60
Socket 7
6x86MX
PR233
166
2x
83
Super7
6x86MX
PR233
187.5
2.5x
75
Super7
6x86MX
PR233
200
3x
66
Socket 7
(continues)
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Continued
Cyrix CPU Type
P-Rating
Actual CPU
Speed (MHz)
Clock
Multiplier
Motherboard
Speed (MHz)
Socket
6x86MX
PR266
207.5
2.5x
83
Super7
6x86MX
PR266
225
3x
75
Super7
6x86MX
PR266
233
3.5x
66
Socket 7
M-II
PR300
225
3x
75
Super7
M-II
PR300
233
3.5x
66
Socket 7
M-II
PR333
250
3x
83
Super7
M-II
PR366
250
2.5x
100
Super7
Not all motherboards support bus speeds such as 40MHz or 55MHz.
A Super7 motherboard is required to support the 100MHz bus speed
Most Super7 motherboards support bus speeds lower than 100MHz
The 6x86MX features 64KB of unified L1 cache and more than double the performance of the
previous 6x86 CPUs. The 6x86MX is offered in clock speeds ranging from 180–266MHz, and like
the 6x86, it is Socket 7 compatible. When running at speeds of 300MHz and higher, the 686MX
was renamed as the MII. Besides the higher speeds, all other functions are virtually identical. All
Cyrix chips were manufactured by other companies such as IBM, who also markets the 6x86
chips under its own name. National began manufacturing Cyrix processors during 1998, but now
that Cyrix is selling them off, the future is unclear.
Note that later versions of the 6x86MX chip have been renamed the MII to deliberately invoke
comparisons with the Pentium II, instead of the regular Pentium processor. The MII chips are not
redesigned; they are, in fact, the same 6x86MX chips as before, only running at higher clock
rates. The first renamed 6x86MX chip is the MII 300, which actually runs at only 233MHz on a
66MHz Socket 7 motherboard. There is also an MII 333, which will run at a 250MHz clock speed
on newer 100MHz Super7 motherboards.
Cyrix also has made an attempt at capturing even more of the low-end market than they already
have by introducing a processor called the MediaGX. This is a low-performance cross between a
486 and a Pentium combined with a custom motherboard chipset in a two-chip package. These
two chips contain everything necessary for a motherboard, except the Super I/O chip, and make
very low-cost PCs possible. Expect to see the MediaGX processors on the lowest end, virtually disposable-type PCs. Later versions of these chips will include more multimedia and even network
support.
IDT Winchip
Another offering in the chip market is from Integrated Device Technology (IDT). A longtime chip
manufacturer who was more well-known for making SRAM (cache memory) chips, IDT acquired
Centaur Technology, who had designed a chip called the C6 Winchip. Now with IDT’s manufacturing capability, the C6 processor became a reality.
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Featuring a very simple design, the C6 Winchip is more like a 486 than a Pentium. It does not
have the superscalar (multiple instruction pipelines) of a Pentium; it has a single high-speed
pipeline instead. Internally, it seems the C6 has little in common with other fifth- and
sixth-generation x86 processors. Even so, according to Centaur, it closely matches the performance of a Pentium MMX when running the Winstone 97 business benchmark, although that
benchmark does not focus on multimedia performance. It also has a much smaller die (88 mm2)
than a typical Pentium, which means it should cost significantly less to manufacture.
The C6 has two large internal caches (32KB each for instructions and data), and will run at 180,
200, 225, and 240MHz. The power consumption is very low—14W maximum at 200MHz for the
desktop chip, and 7.1 to 10.6W for the mobile chips. This processor will likely have some success
in the low-end market.
P-Ratings
To make it easier to understand processor performance, the P-Rating system was jointly developed by Cyrix, IBM Microelectronics, SGS-Thomson Microelectronics, and Advanced Micro
Devices. This new rating, titled the (Performance) P-Rating, equates delivered performance of
microprocessor to that of an Intel Pentium. To determine a specific P-Rating, Cyrix and AMD use
benchmarks such as Winstone 9x. Winstone 9x is a widely used, industry-standard benchmark
that runs a number of Windows-based software applications.
The idea is fine, but in some cases it can be misleading. A single benchmark or even a group of
benchmarks cannot tell the whole story on system or processor performance. In most cases, the
companies selling PR-rated processors have people believing that they are really running at the
speed indicated on the chip. For example, a Cyrix/IBM 6x86MX-PR200 does not really run at
200MHz; instead, it runs at 166MHz. I guess the idea is that it “feels” like 200MHz, or compares
to some Intel processor running at 200MHz (which one?). I am not in favor of the P-Rating system and prefer to just report the processor’s true speed in MHz. If it happens to be 166 but runs
faster than most other 166 processors, so be it—but I don’t like to number it based on some comparison like that.
Note
See “Cyrix P-Ratings” and “AMD P-Ratings” earlier in this chapter to see how P-Ratings stack up against the actual
processor speed in MHz.
The Ziff-Davis Winstone benchmark is used because it is a real-world, application-based benchmark that contains the most popular software applications (based on market share) that run on
a Pentium processor. Winstone also is a widely used benchmark and is freely distributed and
available.
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P1 (086) First-Generation Processors
8088 and 8086 Processors
Intel introduced a revolutionary new processor called the 8086 back in June of 1978. The 8086
was one of the first 16-bit processor chips on the market; at the time virtually all other processors
were 8-bit designs. The 8086 had 16-bit internal registers and could run a new class of software
using 16-bit instructions. It also had a 16-bit external data path, which meant it could transfer
data to memory 16 bits at a time.
The address bus was 20 bits wide, meaning that the 8086 could address a full 1MB (2 to the 20th
power) of memory. This was in stark contrast to most other chips of that time that had 8-bit
internal registers, an 8-bit external data bus, and a 16-bit address bus allowing a maximum of
only 64KB of RAM (2 to the 16th power).
Unfortunately, most of the personal computer world at the time was using 8-bit processors,
which ran 8-bit CP/M (Control Program for Microprocessors) operating systems and software. The
board and circuit designs at the time were largely 8-bit as well. Building a full 16-bit motherboard
and memory system would be costly, pricing such a computer out of the market.
The cost was high because the 8086 needed a 16-bit data bus rather than a less expensive 8-bit
bus. Systems available at that time were 8-bit, and slow sales of the 8086 indicated to Intel that
people weren’t willing to pay for the extra performance of the full 16-bit design. In response,
Intel introduced a kind of crippled version of the 8086, called the 8088. The 8088 essentially
deleted 8 of the 16 bits on the data bus, making the 8088 an 8-bit chip as far as data input and
output were concerned. However, because it retained the full 16-bit internal registers and the 20bit address bus, the 8088 ran 16-bit software and was capable of addressing a full 1MB of RAM.
For these reasons, IBM selected the 8-bit 8088 chip for the original IBM PC. Years later, they were
criticized for using the 8-bit 8088 instead of the 16-bit 8086. In retrospect, it was a very wise decision. IBM even covered up the physical design in their ads, which at the time indicated their new
PC had a “high-speed 16-bit microprocessor.” They could say that because the 8088 still ran the
same powerful 16-bit software the 8086 ran, just a little more slowly. In fact, programmers universally thought of the 8088 as a 16-bit chip because there was virtually no way a program could
distinguish an 8088 from an 8086. This allowed IBM to deliver a PC capable of running a new
generation of 16-bit software, while retaining a much less expensive 8-bit design for the hardware. Because of this, the IBM PC was actually priced less at its introduction than the most popular PC of the time, the Apple II. For the trivia buffs out there, the IBM PC listed for $1,265 and
included only 16KB of RAM, while a similarly configured Apple II cost $1,355.
The original IBM PC used the Intel 8088. The 8088 was introduced in June 1979, but the IBM PC
did not appear until August 1981. Back then, there was often a significant lag time between the
introduction of a new processor and systems that incorporated it. That is unlike today, when new
processors and systems using them are often released on the same day.
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The 8088 in the IBM PC ran at 4.77MHz, or 4,770,000 cycles (essentially computer heartbeats)
per second. Each cycle represents a unit of time to the system, with different instructions or operations requiring one or more cycles to complete. The average instruction on the 8088 took 12
cycles to complete.
Computer users sometimes wonder why a 640KB conventional-memory barrier exists if the 8088
chip can address 1MB of memory. The conventional-memory barrier exists because IBM reserved
384KB of the upper portion of the 1,024KB (1MB) address space of the 8088 for use by adapter
cards and system BIOS. The lower 640KB is the conventional memory in which DOS and software
applications execute.
80186 and 80188 Processors
After Intel produced the 8086 and 8088 chips, it turned its sights toward producing a more powerful chip with an increased instruction set. The company’s first efforts along this line—the
80186 and 80188—were unsuccessful. But incorporating system components into the CPU chip
was an important idea for Intel because it led to faster, better chips, such as the 286.
The relationship between the 80186 and 80188 is the same as that of the 8086 and 8088; one is a
slightly more advanced version of the other. Compared CPU to CPU, the 80186 is almost the
same as the 8088 and has a full 16-bit design. The 80188 (like the 8088) is a hybrid chip that
compromises the 16-bit design with an 8-bit external communications interface. The advantage
of the 80186 and 80188 is that they combine on a single chip 15 to 20 of the 8086–8088 series
system components—a fact that can greatly reduce the number of components in a computer
design. The 80186 and 80188 chips were used for highly intelligent peripheral adapter cards of
that age, such as network adapters.
8087 Coprocessor
Intel introduced the 8086 processor in 1976. The math coprocessor that was paired with the
chip—the 8087—often was called the numeric data processor (NDP), the math coprocessor, or
simply the math chip. The 8087 is designed to perform high-level math operations at many times
the speed of the main processor. The primary advantage of using this chip is the increased execution speed in number-crunching programs, such as spreadsheet applications.
P2 (286) Second-Generation Processors
286 Processors
The Intel 80286 (normally abbreviated as 286) processor did not suffer from the compatibility
problems that damned the 80186 and 80188. The 286 chip, first introduced in 1981, is the CPU
behind the original IBM AT. Other computer makers manufactured what came to be known as
IBM clones, many of these manufacturers calling their systems AT-compatible or AT-class computers.
When IBM developed the AT, it selected the 286 as the basis for the new system because the chip
provided compatibility with the 8088 used in the PC and the XT. That means that software
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written for those chips should run on the 286. The 286 chip is many times faster than the 8088
used in the XT, and it offered a major performance boost to PCs used in businesses. The
processing speed, or throughput, of the original AT (which ran at 6MHz) was five times greater
than that of the PC running at 4.77MHz. The die for the 286 is shown in Figure 3.30.
Figure 3.30
286 Processor die. Photograph used by permission of Intel Corporation.
286 systems are faster than their predecessors for several reasons. The main reason is that 286
processors are much more efficient in executing instructions. An average instruction takes 12
clock cycles on the 8086 or 8088, but an average 4.5 cycles on the 286 processor. Additionally,
the 286 chip can handle up to 16 bits of data at a time through an external data bus twice the
size of the 8088.
The 286 chip has two modes of operation: real mode and protected mode. The two modes are
distinct enough to make the 286 resemble two chips in one. In real mode, a 286 acts essentially
the same as an 8086 chip and is fully object-code compatible with the 8086 and 8088. (A processor
with object-code compatibility can run programs written for another processor without modification and execute every system instruction in the same manner.)
In the protected mode of operation, the 286 was truly something new. In this mode, a program
designed to take advantage of the chip’s capabilities believes that it has access to 1GB of memory
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(including virtual memory). The 286 chip, however, can address only 16MB of hardware memory.
A significant failing of the 286 chip is that it cannot switch from protected mode to real mode
without a hardware reset (a warm reboot) of the system. (It can, however, switch from real mode
to protected mode without a reset.) A major improvement of the 386 over the 286 is that software can switch the 386 from real mode to protected mode, and vice versa. See the section
“Processor Modes,” earlier in this chapter for more information.
Only a small amount of software that took advantage of the 286 chip was sold until Windows 3.0
offered standard mode for 286 compatibility; by that time, the hottest-selling chip was the 386.
Still, the 286 was Intel’s first attempt to produce a CPU chip that supported multitasking, in
which multiple programs run at the same time. The 286 was designed so that if one program
locked up or failed, the entire system didn’t need a warm boot (reset) or cold boot (power off or
on). Theoretically, what happened in one area of memory didn’t affect other programs. Before
multitasked programs could be “safe” from one another, however, the 286 chip (and subsequent
chips) needed an operating system that worked cooperatively with the chip to provide such protection.
80287 Coprocessor
The 80287, internally, is the same math chip as the 8087, although the pins used to plug them
into the motherboard are different. Both the 80287 and the 8087 operate as though they were
identical.
In most systems, the 80286 internally divides the system clock by two to derive the processor
clock. The 80287 internally divides the system-clock frequency by three. For this reason, most ATtype computers run the 80287 at one-third the system clock rate, which also is two-thirds the
clock speed of the 80286. Because the 286 and 287 chips are asynchronous, the interface between
the 286 and 287 chips is not as efficient as with the 8088 and 8087.
In summary, the 80287 and the 8087 chips perform about the same at equal clock rates. The original 80287 is not better than the 8087 in any real way—unlike the 80286, which is superior to
the 8086 and 8088. In most AT systems, the performance gain that you realize by adding the
coprocessor is much less substantial than the same type of upgrade for PC- or XT-type systems or
for the 80386.
286 Processor Problems
After you remove a math coprocessor from an AT-type system, you must rerun your computer’s
Setup program. Some AT-compatible SETUP programs do not properly unset the math coprocessor
bit. If you receive a POST error message because the computer cannot find the math chip, you
might have to unplug the battery from the system board temporarily. All Setup information will
be lost, so be sure to write down the hard drive type, floppy drive type, and memory and video
configurations before unplugging the battery. This information is critical in reconfiguring your
computer correctly.
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P3 (386) Third-Generation Processors
386 Processors
The Intel 80386 (normally abbreviated as 386) caused quite a stir in the PC industry because of
the vastly improved performance it brought to the personal computer. Compared with 8088 and
286 systems, the 386 chip offered greater performance in almost all areas of operation.
The 386 is a full 32-bit processor optimized for high-speed operation and multitasking operating
systems. Intel introduced the chip in 1985, but the 386 appeared in the first systems in late 1986
and early 1987. The Compaq Deskpro 386 and systems made by several other manufacturers
introduced the chip; somewhat later, IBM used the chip in its PS/2 Model 80. The 386 chip rose
in popularity for several years, which peaked around 1991. Obsolete 386 processor systems are
mostly retired or scrapped, having been passed down the user chain. If they are in operating condition, they can be useful for running old DOS or Windows 3.x-based applications, which they
can do quite nicely.
The 386 can execute the real-mode instructions of an 8086 or 8088, but in fewer clock cycles. The
386 was as efficient as the 286 in executing instructions, which means that the average instruction took about 4.5 clock cycles. In raw performance, therefore, the 286 and 386 actually seemed
to be at almost equal clock rates. Many 286 system manufacturers were touting their 16MHz and
20MHz 286 systems as being just as fast as 16MHz and 20MHz 386 systems, and they were right!
The 386 offered greater performance in other ways, mainly because of additional software capability (modes) and a greatly enhanced memory management unit (MMU). The die for the 386 is
shown in Figure 3.31.
The 386 can switch to and from protected mode under software control without a system reset—
a capability that makes using protected mode more practical. In addition, the 386 has a new
mode, called virtual real mode, which enables several real mode sessions to run simultaneously
under protected mode.
The protected mode of the 386 is fully compatible with the protected mode of the 286. The protected mode for both chips often is called their native mode of operation, because these chips are
designed for advanced operating systems such as OS/2 and Windows NT, which run only in protected mode. Intel extended the memory-addressing capabilities of 386 protected mode with a
new MMU that provided advanced memory paging and program switching. These features were
extensions of the 286 type of MMU, so the 386 remained fully compatible with the 286 at the
system-code level.
The 386 chip’s virtual real mode was new. In virtual real mode, the processor could run with
hardware memory protection while simulating an 8086’s real-mode operation. Multiple copies of
DOS and other operating systems, therefore, could run simultaneously on this processor, each in
a protected area of memory. If the programs in one segment crashed, the rest of the system was
protected. Software commands could reboot the blown partition.
Numerous variations of the 386 chip exist, some of which are less powerful and some of which
are less power-hungry. The following sections cover the members of the 386-chip family and
their differences.
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Figure 3.31
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113
386 processor die. Photograph used by permission of Intel Corporation.
386DX Processors
The 386DX chip was the first of the 386 family members that Intel introduced. The 386 is a full
32-bit processor with 32-bit internal registers, a 32-bit internal data bus, and a 32-bit external
data bus. The 386 contains 275,000 transistors in a VLSI (very large scale integration) circuit. The
chip comes in a 132-pin package and draws approximately 400 milliamperes (ma), which is less
power than even the 8086 requires. The 386 has a smaller power requirement because it is made
of CMOS (complementary metal oxide semiconductor) materials. The CMOS design enables
devices to consume extremely low levels of power.
The Intel 386 chip was available in clock speeds ranging from 16–33MHz; other manufacturers,
primarily AMD and Cyrix, offered comparable versions with speeds up to 40MHz.
The 386DX can address 4GB of physical memory. Its built in virtual memory manager enables
software designed to take advantage of enormous amounts of memory to act as though a system
has 64TB of memory. (A terabyte (TB) is 1,099,511,627,776 bytes of memory, or about 1,000GB.)
386SX Processors
The 386SX was designed for systems designers who were looking for 386 capabilities at 286 system prices. Like the 286, the 386SX is restricted to only 16 bits when communicating with other
system components, such as memory. Internally, however, the 386SX is identical to the DX chip;
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the 386SX has 32-bit internal registers and can therefore run 32-bit software. The 386SX uses a
24-bit memory-addressing scheme like that of the 286, rather than the full 32-bit memory
address bus of the standard 386. The 386SX, therefore, can address a maximum 16MB of physical
memory rather than the 4GB of physical memory that the 386DX can address. Before it was discontinued, the 386SX was available in clock speeds ranging from 16–33MHz.
The 386SX signaled the end of the 286 because of the 386SX chip’s superior MMU and the addition of the virtual real mode. Under a software manager such as Windows or OS/2, the 386SX can
run numerous DOS programs at the same time. The capability to run 386-specific software is
another important advantage of the 386SX over any 286 or older design. For example, Windows
3.1 runs nearly as well on a 386SX as it does on a 386DX.
Note
One common fallacy about the 386SX is that you can plug one into a 286 system and give the system 386 capabilities. This is not true; the 386SX chip is not pin-compatible with the 286 and does not plug into the same socket.
Several upgrade products, however, have been designed to adapt the chip to a 286 system. In terms of raw
speed, converting a 286 system to a 386 CPU chip results in little performance gain—286 motherboards are built
with a restricted 16-bit interface to memory and peripherals. A 16MHz 386SX is not markedly faster than a
16MHz 286, but it does offer improved memory management capabilities on a motherboard designed for it, and
the capability to run 386-specific software.
386SL Processors
The 386SL is another variation on the 386 chip. This low-power CPU had the same capabilities as
the 386SX, but it was designed for laptop systems in which low power consumption was needed.
The SL chips offered special power-management features that were important to systems that ran
on batteries. The SL chip also offered several sleep modes to conserve power.
The chip included an extended architecture that contained a System Management Interrupt
(SMI), which provided access to the power-management features. Also included in the SL chip
was special support for LIM (Lotus Intel Microsoft) expanded memory functions and a cache controller. The cache controller was designed to control a 16–64KB external processor cache.
These extra functions account for the higher transistor count in the SL chips (855,000) compared
with even the 386DX processor (275,000). The 386SL was available in 25MHz clock speed.
Intel offered a companion to the 386SL chip for laptops called the 82360SL I/O subsystem. The
82360SL provided many common peripheral functions such as serial and parallel ports, a direct
memory access (DMA) controller, an interrupt controller, and power-management logic for the
386SL processor. This chip subsystem worked with the processor to provide an ideal solution for
the small size and low power-consumption requirements of portable and laptop systems.
80387 Coprocessor
Although the 80387 chips ran asynchronously, 386 systems were designed so that the math chip
runs at the same clock speed as the main CPU. Unlike the 80287 coprocessor, which was merely
an 8087 with different pins to plug into the AT motherboard, the 80387 coprocessor was a highperformance math chip designed specifically to work with the 386.
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All 387 chips used a low power-consumption CMOS design. The 387 coprocessor had two basic
designs: the 387DX coprocessor, which was designed to work with the 386DX processor, and the
387SX coprocessor, which was designed to work with the 386SX, SL, or SLC processors.
Intel originally offered several speeds for the 387DX coprocessor. But when the company
designed the 33MHz version, a smaller mask was required to reduce the lengths of the signal
pathways in the chip. This increased the performance of the chip by roughly 20 percent.
Note
Because Intel lagged in developing the 387 coprocessor, some early 386 systems were designed with a socket
for a 287 coprocessor. Performance levels associated with that union, however, leave much to be desired.
Installing a 387DX is easy, but you must be careful to orient the chip in its socket properly; otherwise, the chip will be destroyed. The most common cause of burned pins on the 387DX is
incorrect installation. In many systems, the 387DX was oriented differently from other large
chips. Follow the manufacturer’s installation instructions carefully to avoid damaging the 387DX;
Intel’s warranty does not cover chips that are installed incorrectly.
Several manufacturers developed their own versions of the Intel 387 coprocessors, some of which
were touted as being faster than the original Intel chips. The general compatibility record of these
chips was very good.
Weitek Coprocessors
In 1981, several Intel engineers formed the Weitek Corporation. Weitek developed math
coprocessors for several systems, including those based on Motorola processor designs. Intel originally contracted Weitek to develop a math coprocessor for the Intel 386 CPU, because Intel was
behind in its own development of the 387 math coprocessor. The result was the Weitek 1167, a
custom math coprocessor that uses a proprietary Weitek instruction set, which is incompatible
with the Intel 387.
To use the Weitek coprocessor, your system must have the required additional socket, which was
different from the standard Intel coprocessor sockets.
80386 Bugs
Some early 16MHz Intel 386DX processors had a small bug that appeared as a software problem.
The bug, which apparently was in the chip’s 32-bit multiply routine, manifested itself only when
you ran true 32-bit code in a program such as OS/2 2.x, UNIX/386, or Windows in enhanced
mode. Some specialized 386 memory-management software systems also may invoke this subtle
bug, but 16-bit operating systems (such as DOS and OS/2 1.x) probably will not.
The bug usually causes the system to lock up. Diagnosing this problem can be difficult because
the problem generally is intermittent and software-related. Running tests to find the bug is difficult; only Intel, with proper test equipment, can determine whether your chip has a bug. Some
programs can diagnose the problem and identify a defective chip, but they cannot identify all
defective chips. If a program indicates a bad chip, you certainly have a defective one; if the program passes the chip, you still might have a defective one.
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Intel requested that its 386 customers return possibly defective chips for screening, but many
vendors did not return them. Intel tested returned chips and replaced defective ones. The defective chips later were sold to bargain liquidators or systems houses that wanted chips that would
not run 32-bit code. The defective chips were stamped with a 16-bit SW Only logo, indicating
that they were authorized to run only 16-bit software.
Chips that passed the test, and all subsequent chips produced as bug-free, were marked with a
double-sigma code (SS). 386DX chips that are not marked with either of these designations have
not been tested by Intel and might be defective.
The following marking indicates that a chip has not yet been screened for the defect; it might be
either good or bad.
80386-16
The following marking indicates that the chip has been tested and has the 32-bit multiply bug.
The chip works with 16-bit software (such as DOS) but not with 32-bit, 386-specific software
(such as Windows or OS/2).
80386-16
16-bit SW Only
The following mark on a chip indicates that it has been tested as defect-free. This chip fulfills all
the capabilities promised for the 80386.
80386-16
SS
This problem was discovered and corrected before Intel officially added DX to the part number.
So, if you have a chip labeled as 80386DX or 386DX, it does not have this problem.
Another problem with the 386DX can be stated more specifically. When 386-based versions of
XENIX or other UNIX implementations are run on a computer that contains a 387DX math
coprocessor, the computer locks up under certain conditions. The problem does not occur in the
DOS environment, however. For the lockup to occur, all the following conditions must be in
effect:
■ Demand page virtual memory must be active.
■ A 387DX must be installed and in use.
■ DMA (direct memory access) must occur.
■ The 386 must be in a wait state.
When all these conditions are true at the same instant, the 386DX ends up waiting for the
387DX and vice versa. Both processors will continue to wait for each other indefinitely. The problem is in certain versions of the 386DX, not in the 387DX math coprocessor.
Intel published this problem (Errata 21) immediately after it was discovered to inform its OEM
customers. At that point, it became the responsibility of each manufacturer to implement a fix in
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its hardware or software product. Some manufacturers, such as Compaq and IBM, responded by
modifying their motherboards to prevent these lockups from occurring.
The Errata 21 problem occurs only in the B stepping version of the 386DX and not in the later D
stepping version. You can identify the D stepping version of the 386DX by the letters DX in the
part number (for example, 386DX-20). If DX is part of the chip’s part number, the chip does not
have this problem.
P4 (486) Fourth-Generation Processors
486 Processors
In the race for more speed, the Intel 80486 (normally abbreviated as 486) was another major leap
forward. The additional power available in the 486 fueled tremendous growth in the software
industry. Tens of millions of copies of Windows, and millions of copies of OS/2, have been sold
largely because the 486 finally made the GUI of Windows and OS/2 a realistic option for people
who work on their computers every day.
Four main features make a given 486 processor roughly twice as fast as an equivalent MHz 386
chip. These features are
■ Reduced instruction-execution time. A single instruction in the 486 takes an average of only
two clock cycles to complete, compared with an average of more than four cycles on the
386. Clock-multiplied versions such as the DX2 and DX4 further reduced this to about two
cycles per instruction.
■ Internal (Level 1) cache. The built-in cache has a hit ratio of 90–95 percent, which describes
how often zero-wait-state read operations will occur. External caches can improve this ratio
further.
■ Burst-mode memory cycles. A standard 32-bit (4-byte) memory transfer takes two clock cycles.
After a standard 32-bit transfer, more data up to the next 12 bytes (or three transfers) can
be transferred with only one cycle used for each 32-bit (4-byte) transfer. Thus, up to 16
bytes of contiguous, sequential memory data can be transferred in as little as five cycles
instead of eight cycles or more. This effect can be even greater when the transfers are only
8 bits or 16 bits each.
◊◊ See “Burst EDO,” p. 428.
■ Built-in (synchronous) enhanced math coprocessor (some versions). The math coprocessor runs
synchronously with the main processor and executes math instructions in fewer cycles
than previous designs did. On average, the math coprocessor built into the DX-series chips
provides two to three times greater math performance than an external 387 chip.
The 486 chip is about twice as fast as the 386, which means that a 386DX-40 is about as fast as a
486SX-20. This made the 486 a much more desirable option, primarily because it could more easily be upgraded to a DX2 or DX4 processor at a later time. You can see why the arrival of the 486
rapidly killed off the 386 in the marketplace.
Before the 486, many people avoided GUIs because they didn’t have time to sit around waiting
for the hourglass, which indicates that the system is performing behind-the-scenes operations
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that the user cannot interrupt. The 486 changed that situation. Many people believe that the 486
CPU chip spawned the widespread acceptance of GUIs.
With the release of its faster Pentium CPU chip, Intel began to cut the price of the 486 line to
entice the industry to shift over to the 486 as the mainstream system. Intel later did the same
thing with its Pentium chips, spelling the end of the 486 line. The 486 is now offered by Intel
only for use in embedded microprocessor applications, used primarily in expansion cards.
Most of the 486 chips were offered in a variety of maximum speed ratings, varying from 16MHz
up to 120MHz. Additionally, 486 processors have slight differences in overall pin configurations.
The DX, DX2, and SX processors have a virtually identical 168-pin configuration, whereas the
OverDrive chips have either the standard 168-pin configuration or a specially modified 169-pin
OverDrive (sometimes also called 487SX) configuration. If your motherboard has two sockets, the
primary one likely supports the standard 168-pin configuration, and the secondary (OverDrive)
socket supports the 169-pin OverDrive configuration. Most newer motherboards with a single ZIF
socket support any of the 486 processors except the DX4. The DX4 is different because it requires
3.3v to operate instead of 5v, like most other chips up to that time.
A processor rated for a given speed always functions at any of the lower speeds. A 100MHz-rated
486DX4 chip, for example, runs at 75MHz if it is plugged into a 25MHz motherboard. Note that
the DX2/OverDrive processors operate internally at two times the motherboard clock rate,
whereas the DX4 processors operate at two, two and a half, or three times the motherboard clock
rate. Table 3.19 shows the different speed combinations that can result from using the DX2 or
DX4 processors with different motherboard clock speeds.
Table 3.19
Speeds
Intel DX2 and DX4 Operating Speeds Versus Motherboard Clock
DX2
(2× mode)
Speed
DX4(2.5× mode)
Speed
DX4
(3× mode)
Speed
DX4
16MHz
Motherboard
32MHz
32MHz
40MHz
48MHz
40MHz
Motherboard
80MHz
80MHz
100MHz
120MHz
20MHz
Motherboard
40MHz
40MHz
50MHz
60MHz
50MHz
Motherboard
n/a
100MHz
n/a
n/a
25MHz
Motherboard
50MHz
50MHz
63MHz
75MHz
33MHz
Motherboard
66MHz
66MHz
83MHz
100MHz
Processor speed
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The internal core speed of the DX4 processor is controlled by the CLKMUL (Clock Multiplier) signal at pin R-17 (Socket 1) or S-18 (Socket 2, 3, or 6). The CLKMUL input is sampled only during a
reset of the CPU, and defines the ratio of the internal clock to the external bus frequency CLK
signal at pin C-3 (Socket 1) or D-4 (Socket 2, 3, or 6). If CLKMUL is sampled low, the internal
core speed will be two times the external bus frequency. If driven high or left floating (most
motherboards would leave it floating), triple speed mode is selected. If the CLKMUL signal is connected to the BREQ (Bus Request) output signal at pin Q-15 (Socket 1) or R-16 (Socket 2, 3, or 6),
the CPU internal core speed will be two and a half times the CLK speed. To summarize, here is
how the socket has to be wired for each DX4 speed selection:
CPU Speed
CLKMUL (Sampled Only at CPU Reset)
2x
Low
2.5x
Connected to BREQ
3x
High or Floating
You will have to determine how your particular motherboard is wired and whether it can be
changed to alter the CPU core speed in relation to the CLK signal. In most cases, there would be
one or two jumpers on the board near the processor socket. The motherboard documentation
should cover these settings if they can be changed.
One interesting capability here is to run the DX4-100 chip in a doubled mode with a 50MHz
motherboard speed. This would give you a very fast memory bus, along with the same 100MHz
processor speed, as if you were running the chip in a 33/100MHz tripled mode.
Note
One caveat is that if your motherboard has VL-Bus slots, they will have to be slowed down to 33 or 40MHz to
operate properly.
Many VL-Bus motherboards can run the VL-Bus slots in a buffered mode, add wait states, or even
selectively change the clock only for the VL-Bus slots to keep them compatible. In most cases,
they will not run properly at 50MHz. Consult your motherboard—or even better, your chipset
documentation—to see how your board is set up.
Caution
If you are upgrading an existing system, be sure that your socket will support the chip that you are installing. In particular, if you are putting a DX4 processor in an older system, you need some type of adapter to regulate the voltage down to 3.3v. If you put the DX4 in a 5v socket, you will destroy the chip! See the earlier section on
processor sockets for more information.
The 486-processor family is designed for greater performance than previous processors because it
integrates formerly external devices, such as cache controllers, cache memory, and math
coprocessors. Also, 486 systems were the first designed for true processor upgradability. Most 486
systems can be upgraded by simple processor additions or swaps that can effectively double the
speed of the system.
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486DX Processors
The original Intel 486DX processor was introduced on April 10, 1989, and systems using this chip
first appeared during 1990. The first chips had a maximum speed rating of 25MHz; later versions
of the 486DX were available in 33MHz- and 50MHz-rated versions. The 486DX originally was
available only in a 5v, 168-pin PGA version, but now is also available in 5v, 196-pin PQFP
(Plastic Quad Flat Pack) and 3.3v, 208-pin SQFP (Small Quad Flat Pack). These latter form factors
are available in SL Enhanced versions, which are intended primarily for portable or laptop applications in which saving power is important.
Two main features separate the 486 processor from older processors:
■ The 486DX integrates functions such as the math coprocessor, cache controller, and cache
memory into the chip.
■ The 486 also was designed with upgradability in mind; double-speed OverDrive are
upgrades available for most systems.
The 486DX processor is fabricated with low-power CMOS (complementary metal oxide semiconductor) technology. The chip has a 32-bit internal register size, a 32-bit external data bus, and a
32-bit address bus. These dimensions are equal to those of the 386DX processor. The internal register size is where the “32-bit” designation used in advertisements comes from. The 486DX chip
contains 1.2 million transistors on a piece of silicon no larger than your thumbnail. This figure is
more than four times the number of components on 386 processors and should give you a good
indication of the 486 chip’s relative power. The die for the 486 is shown in Figure 3.32.
The standard 486DX contains a processing unit, a floating-point unit (math coprocessor), a
memory-management unit, and a cache controller with 8KB of internal-cache RAM. Due to the
internal cache and a more efficient internal processing unit, the 486 family of processors can execute individual instructions in an average of only two processor cycles. Compare this figure with
the 286 and 386 families, both of which execute an average 4.5 cycles per instruction. Compare it
also with the original 8086 and 8088 processors, which execute an average 12 cycles per instruction. At a given clock rate (MHz), therefore, a 486 processor is roughly twice as efficient as a 386
processor; a 16MHz 486SX is roughly equal to a 33MHz 386DX system; and a 20MHz 486SX is
equal to a 40MHz 386DX system. Any of the faster 486s are way beyond the 386 in performance.
The 486 is fully instruction-set–compatible with previous Intel processors, such as the 386, but
offers several additional instructions (most of which have to do with controlling the internal
cache).
Like the 386DX, the 486 can address 4GB of physical memory and manage as much as 64TB of
virtual memory. The 486 fully supports the three operating modes introduced in the 386: real
mode, protected mode, and virtual real mode.
■ In real mode, the 486 (like the 386) runs unmodified 8086-type software.
■ In protected mode, the 486 (like the 386) offers sophisticated memory paging and program
switching.
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■ In virtual real mode, the 486 (like the 386) can run multiple copies of DOS or other operating systems while simulating an 8086’s real mode operation. Under an operating system
such as Windows or OS/2, therefore, both 16-bit and 32-bit programs can run simultaneously on this processor with hardware memory protection. If one program crashes, the rest
of the system is protected, and you can reboot the blown portion through various means,
depending on the operating software.
Figure 3.32
486 processor die. Photograph used by permission of Intel Corporation.
The 486DX series has a built-in math coprocessor that sometimes is called an MCP (math
coprocessor) or FPU (floating-point unit). This series is unlike previous Intel CPU chips, which
required you to add a math coprocessor if you needed faster calculations for complex mathematics. The FPU in the 486DX series is 100 percent software-compatible with the external 387 math
coprocessor used with the 386, but it delivers more than twice the performance. It runs in synchronization with the main processor and executes most instructions in half as many cycles as
the 386.
486SL
The 486SL was a short-lived, standalone chip. The SL enhancements and features became available in virtually all the 486 processors (SX, DX, and DX2) in what are called SL enhanced versions. SL enhancement refers to a special design that incorporates special power-saving features.
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The SL enhanced chips originally were designed to be installed in laptop or notebook systems
that run on batteries, but they found their way into desktop systems, as well. The SL enhanced
chips featured special power-management techniques, such as sleep mode and clock throttling, to
reduce power consumption when necessary. These chips were available in 3.3v versions, as well.
Intel designed a power-management architecture called system management mode (SMM). This
mode of operation is totally isolated and independent from other CPU hardware and software.
SMM provides hardware resources such as timers, registers, and other I/O logic that can control
and power down mobile-computer components without interfering with any of the other system
resources. SMM executes in a dedicated memory space called system management memory,
which is not visible and does not interfere with operating system and application software. SMM
has an interrupt called system management interrupt (SMI), which services power-management
events and is independent from, and higher priority than, any of the other interrupts.
SMM provides power management with flexibility and security that were not available previously.
For example, an SMI occurs when an application program tries to access a peripheral device that
is powered down for battery savings, which powers up the peripheral device and reexecutes the
I/O instruction automatically.
Intel also designed a feature called suspend/resume in the SL processor. The system manufacturer
can use this feature to provide the portable computer user with instant-on-and-off capability. An
SL system typically can resume (instant on) in one second from the suspend state (instant off) to
exactly where it left off. You do not need to reboot, load the operating system, load the application program, and then load the application data. Simply push the Suspend/Resume button and
the system is ready to go.
The SL CPU was designed to consume almost no power in the suspend state. This feature means
that the system can stay in the suspend state possibly for weeks and yet start up instantly right
where it left off. An SL system can keep working data in normal RAM memory safe for a long
time while it is in the suspend state, but saving to a disk still is prudent.
486SX
The 486SX, introduced in April 1991, was designed to be sold as a lower cost version of the 486.
The 486SX is virtually identical to the full DX processor, but the chip does not incorporate the
FPU or math coprocessor portion.
As you read earlier in this chapter, the 386SX was a scaled-down (some people would say crippled) 16-bit version of the full-blown 32-bit 386DX. The 386SX even had a completely different
pinout and was not interchangeable with the more powerful DX version. The 486SX, however, is
a different story. The 486SX is, in fact, a full-blown 32-bit 486 processor that is basically
pin-compatible with the DX. A few pin functions are different or rearranged, but each pin fits
into the same socket.
The 486SX chip is more a marketing quirk than new technology. Early versions of the 486SX chip
actually were DX chips that showed defects in the math-coprocessor section. Instead of being
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scrapped, the chips were packaged with the FPU section disabled and sold as SX chips. This
arrangement lasted for only a short time; thereafter, SX chips got their own mask, which is different from the DX mask. (A mask is the photographic blueprint of the processor and is used to etch
the intricate signal pathways into a silicon chip.) The transistor count dropped to 1.185 million
(from 1.2 million) to reflect this new mask.
The 486SX chip is twice as fast as a 386DX with the same clock speed. Intel marketed the 486SX
as being the ideal chip for new computer buyers, because fewer entry-level programs of that day
used math-coprocessor functions.
The 486SX was normally available in 16, 20, 25, and 33MHz-rated speeds, and there was also a
486 SX/2 that ran at up to 50 or 66MHz. The 486SX normally comes in a 168-pin version,
although other surface-mount versions are available in SL enhanced models.
Despite what Intel’s marketing and sales information implies, no technical provision exists for
adding a separate math coprocessor to a 486SX system; neither is a separate math coprocessor
chip available to plug in. Instead, Intel wanted you to add a new 486 processor with a built-in
math unit and disable the SX CPU that already was on the motherboard. If this situation sounds
confusing, read on, because this topic brings you to the most important aspect of 486 design:
upgradability.
487SX
The 487SX math coprocessor, as Intel calls it, really is a complete 25MHz 486DX CPU with an
extra pin added and some other pins rearranged. When the 487SX is installed in the extra socket
provided in a 486SX CPU-based system, the 487SX turns off the existing 486SX via a new signal
on one of the pins. The extra key pin actually carries no signal itself and exists only to prevent
improper orientation when the chip is installed in a socket.
The 487SX takes over all CPU functions from the 486SX and also provides math coprocessor
functionality in the system. At first glance, this setup seems rather strange and wasteful, so perhaps further explanation is in order. Fortunately, the 487SX turned out to be a stopgap measure
while Intel prepared its real surprise: the OverDrive processor. The DX2/OverDrive speed-doubling chips, which are designed for the 487SX 169-pin socket, have the same pinout as the
487SX. These upgrade chips are installed in exactly the same way as the 487SX; therefore, any
system that supports the 487SX also supports the DX2/OverDrive chips.
Although in most cases you can upgrade a system by removing the 486SX CPU and replacing it
with a 487SX (or even a DX or DX2/OverDrive), Intel originally discouraged this procedure.
Instead, Intel recommended that PC manufacturers include a dedicated upgrade (OverDrive)
socket in their systems, because several risks were involved in removing the original CPU from a
standard socket. (The following section elaborates on those risks.) Now Intel recommends—or
even insists on—the use of a single processor socket of a ZIF design, which makes upgrading an
easy task physically.
√√ See “Zero Insertion Force (ZIF) Sockets,” p. 86.
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Very few early 486 systems had a socket for the Weitek 4167 coprocessor chip for 486 systems
that existed in November 1989.
DX2/OverDrive and DX4 Processors
On March 3, 1992, Intel introduced the DX2 speed-doubling processors. On May 26, 1992, Intel
announced that the DX2 processors also would be available in a retail version called OverDrive.
Originally, the OverDrive versions of the DX2 were available only in 169-pin versions, which
meant that they could be used only with 486SX systems that had sockets configured to support
the rearranged pin configuration.
On September 14, 1992, Intel introduced 168-pin OverDrive versions for upgrading 486DX systems. These processors could be added to existing 486 (SX or DX) systems as an upgrade, even if
those systems did not support the 169-pin configuration. When you use this processor as an
upgrade, you install the new chip in your system, which subsequently runs twice as fast.
The DX2/OverDrive processors run internally at twice the clock rate of the host system. If the
motherboard clock is 25MHz, for example, the DX2/OverDrive chip runs internally at 50MHz;
likewise, if the motherboard is a 33MHz design, the DX2/OverDrive runs at 66MHz. The
DX2/OverDrive speed doubling has no effect on the rest of the system; all components on the
motherboard run the same as they do with a standard 486 processor. Therefore, you do not have
to change other components (such as memory) to accommodate the double-speed chip. The
DX2/OverDrive chips have been available in several speeds. Three different speed-rated versions
have been offered:
■ 40MHz DX2/OverDrive for 16MHz or 20MHz systems
■ 50MHz DX2/OverDrive for 25MHz systems
■ 66MHz DX2/OverDrive for 33MHz systems
Notice that these ratings indicate the maximum speed at which the chip is capable of running.
You could use a 66MHz-rated chip in place of the 50MHz- or 40MHz-rated parts with no problem, although the chip will run only at the slower speeds. The actual speed of the chip is double
the motherboard clock frequency. When the 40MHz DX2/OverDrive chip is installed in a 16MHz
486SX system, for example, the chip will function only at 32MHz—exactly double the motherboard speed. Intel originally stated that no 100MHz DX2/OverDrive chip would be available for
50MHz systems—which technically has not been true, because the DX4 could be set to run in a
clock-doubled mode and used in a 50MHz motherboard (see the discussion of the DX4 processor
in this section).
The only part of the DX2 chip that doesn’t run at double speed is the bus interface unit, a region
of the chip that handles I/O between the CPU and the outside world. By translating between the
differing internal and external clock speeds, the bus interface unit makes speed doubling transparent to the rest of the system. The DX2 appears to the rest of the system to be a regular 486DX
chip, but one that seems to execute instructions twice as fast.
DX2/OverDrive chips are based on the 0.8 micron circuit technology that was first used in the
50MHz 486DX. The DX2 contains 1.1 million transistors in a three-layer form. The internal 8KB
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cache, integer, and floating-point units all run at double speed. External communication with the
PC runs at normal speed to maintain compatibility.
Besides upgrading existing systems, one of the best parts of the DX2 concept was the fact that
system designers could introduce very fast systems by using cheaper motherboard designs, rather
than the more costly designs that would support a straight high-speed clock. This means that a
50MHz 486DX2 system was much less expensive than a straight 50MHz 486DX system. The system board in a 486DX-50 system operates at a true 50MHz. The 486DX2 CPU in a 486DX2-50
system operates internally at 50MHz, but the motherboard operates at only 25MHz.
You may be thinking that a true 50MHz DX processor–based system still would be faster than a
speed-doubled 25MHz system, and this generally is true. But, the differences in speed actually are
very slight—a real testament to the integration of the 486 processor and especially to the cache
design.
When the processor has to go to system memory for data or instructions, for example, it has to
do so at the slower motherboard operating frequency (such as 25MHz). Because the 8KB internal
cache of the 486DX2 has a hit rate of 90–95 percent, however, the CPU has to access system
memory only 5–10 percent of the time for memory reads. Therefore, the performance of the DX2
system can come very close to that of a true 50MHz DX system and cost much less. Even though
the motherboard runs only at 33.33MHz, a system with a DX2 66MHz processor ends up being
faster than a true 50MHz DX system, especially if the DX2 system has a good L2 cache.
Many 486 motherboard designs also include a secondary cache that is external to the cache integrated into the 486 chip. This external cache allows for much faster access when the 486 chip
calls for external-memory access. The size of this external cache can vary anywhere from 16KB to
512K or more. When you add a DX2 processor, an external cache is even more important for
achieving the greatest performance gain. This cache greatly reduces the wait states that the
processor will have to add when writing to system memory or when a read causes an internal
cache miss. For this reason, some systems perform better with the DX2/OverDrive processors
than others, usually depending on the size and efficiency of the external-memory cache system
on the motherboard. Systems that have no external cache will still enjoy a near-doubling of CPU
performance, but operations that involve a great deal of memory access will be slower.
This brings us to the DX4 processor. Although the standard DX4 technically was not sold as a
retail part, it could be purchased from several vendors, along with the 3.3v voltage adapter
needed to install the chip in a 5v socket. These adapters have jumpers that enable you to select
the DX4 clock multiplier and set it to 2x, 2.5x, or 3x mode. In a 50MHz DX system, you could
install a DX4/voltage-regulator combination set in 2x mode for a motherboard speed of 50MHz
and a processor speed of 100MHz! Although you may not be able to take advantage of certain VLBus adapter cards, you will have one of the fastest 486-class PCs available.
Intel also sold a special DX4 OverDrive processor that included a built-in voltage regulator and
heat sink that are specifically designed for the retail market. The DX4 OverDrive chip is essentially the same as the standard 3.3v DX4 with the main exception that it runs on 5v because it
includes an on-chip regulator. Also, the DX4 OverDrive chip will run only in the tripled speed
mode, and not the 2x or 2.5x modes of the standard DX4 processor.
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Note
As of this writing, Intel has discontinued all 486 and DX2/DX4/OverDrive processors, including the so-called
Pentium OverDrive processor.
Pentium OverDrive for 486SX2 and DX2 Systems
The Pentium OverDrive Processor became available in 1995. An OverDrive chip for 486DX4 systems had been planned, but poor marketplace performance of the SX2/DX2 chip meant that it
never saw the light of day. One thing to keep in mind about the 486 Pentium OverDrive chip is
that although it is intended primarily for SX2 and DX2 systems, it should work in any upgradable 486SX or DX system that has a Socket 2 or Socket 3. If in doubt, check Intel’s online upgrade
guide for compatibility.
The Pentium OverDrive processor is designed for systems that have a processor socket that follows the Intel Socket 2 specification. This processor also will work in systems that have a Socket 3
design, although you should ensure that the voltage is set for 5v rather than 3.3v. The Pentium
OverDrive chip includes a 32KB internal L1 cache, and the same superscalar (multiple instruction
path) architecture of the real Pentium chip. Besides a 32-bit Pentium core, these processors feature increased clock-speed operation due to internal clock multiplication and incorporate an
internal write-back cache (standard with the Pentium). If the motherboard supports the writeback cache function, increased performance will be realized. Unfortunately, most motherboards,
especially older ones with the Socket 2 design, only support write-through cache.
Most tests of these OverDrive chips show them to be only slightly ahead of the DX4-100 and
behind the DX4-120 and true Pentium 60, 66, or 75. Unfortunately, these are the only solutions
still offered by Intel for upgrading the 486. Based on the relative affordability of low-end “real”
Pentiums (in their day), it was hard not to justify making the step up to a Pentium system. At the
time, I did not recommend the 486 Pentium OverDrive chips as a viable solution for the future.
”Vacancy”—Secondary OverDrive Sockets
Perhaps you saw the Intel advertisements—both print and television—that featured a 486SX system with a neon Vacancy sign pointing to an empty socket next to the CPU chip. Unfortunately,
these ads were not very informative, and they made it seem that only systems with the extra
socket could be upgraded. I was worried when I first saw these ads because I had just purchased a
486DX system, and the advertisements implied that only 486SX systems with the empty
OverDrive socket were upgradable. This, of course, was not true, but the Intel advertisements did
not communicate that fact very well.
I later found that upgradability does not depend on having an extra OverDrive socket in the system and that virtually any 486SX or DX system can be upgraded. The secondary OverDrive
socket was designed to make upgrading easier and more convenient. Even in systems that have
the second socket, you can actually remove the primary SX or DX CPU and plug the OverDrive
processor directly into the main CPU socket, rather than into the secondary OverDrive socket.
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In that case, you would have an upgraded system with a single functioning CPU installed; you
could remove the old CPU from the system and sell it or trade it in for a refund. Unfortunately,
Intel does not offer a trade-in or core-charge policy; it does not want your old chip. For this reason, some people saw the OverDrive socket as being a way for Intel to sell more CPUs. Some valid
reasons exist, however, to use the OverDrive socket and leave the original CPU installed.
One reason is that many PC manufacturers void the system warranty if the CPU has been
removed from the system. Also, most manufacturers require that the system be returned with
only the original parts when systems are serviced; you must remove all add-in cards, memory
modules, upgrade chips, and similar items before sending the system in for servicing. If you
replace the original CPU when you install the upgrade, returning the system to its original condition will be much more difficult.
Another reason for using the upgrade socket is that the system will not function if the main CPU
socket is damaged when you remove the original CPU or install the upgrade processor. By contrast, if a secondary upgrade socket is damaged, the system still should work with the original
CPU.
80487 Upgrade
The Intel 80486 processor was introduced in late 1989, and systems using this chip appeared during 1990. The 486DX integrated the math coprocessor into the chip.
The 486SX began life as a full-fledged 486DX chip, but Intel actually disabled the built-in math
coprocessor before shipping the chip. As part of this marketing scheme, Intel marketed what it
called a 487SX math coprocessor. Motherboard manufacturers installed an Intel-designed socket
for this so-called 487 chip. In reality, however, the 487SX math chip was a special 486DX chip
with the math coprocessor enabled. When you plugged this chip into your motherboard, it disabled the 486SX chip and gave you the functional equivalent of a full-fledged 486DX system.
AMD 486 (5x86)
AMD makes a line of 486-compatible chips that install into standard 486 motherboards. In fact,
AMD makes the fastest 486 processor available, which they call the Am5x86(TM)-P75. The name
is a little misleading, as the 5x86 part makes some people think that this is a fifth-generation
Pentium-type processor. In reality, it is a fast clock-multiplied (4x clock) 486 that runs at four
times the speed of the 33MHz 486 motherboard you plug it into.
The 5x85 offers high-performance features such as a unified 16KB write-back cache and 133MHz
core clock speed; it is approximately comparable to a Pentium 75, which is why it is denoted
with a P-75 in the part number. It is the ideal choice for cost-effective 486 upgrades, where
changing the motherboard is difficult or impossible.
Not all motherboards support the 5x86. The best way to verify that your motherboard supports
the chip is by checking with the documentation that came with the board. Look for keywords
such as “Am5X86,” “AMD-X5,” “clock-quadrupled,” “133MHz,” or other similar wording.
Another good way to determine whether your motherboard supports the AMD 5x86 is to look for
it in the listed models on AMD’s Web site.
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There are a few things to note when installing a 5x86 processor into a 486 motherboard:
■ The operating voltage for the 5x86 is 3.45v +/- 0.15v. Not all motherboards may have this
setting, but most that incorporate a Socket 3 design should. If your 486 motherboard is a
Socket 1 or 2 design, you cannot use the 5x86 processor directly. The 3.45 volt processor
will not operate in a 5-volt socket and may be damaged. To convert a 5-volt motherboard
to 3.45 volts, adapters can be purchased from several vendors including Kingston,
Evergreen, and AMP. In fact, Kingston and Evergreen sell the 5x86 complete with a voltage
regulator adapter attached in an easy-to-install package. These versions are ideal for older
486 motherboards that don’t have a Socket 3 design.
■ It is generally better to purchase a new motherboard with Socket 3 than to buy one of these
adapters; however, 486 motherboards are hard to find these days, and your old board may
be in a proprietary form factor for which it is impossible to find a replacement. Buying a
new motherboard is also better than using an adapter because the older BIOS may not
understand the requirements of the processor as far as speed is concerned. BIOS updates are
often required with older boards.
■ Most Socket 3 motherboards have jumpers, allowing you to set the voltage manually. Some
boards don’t have jumpers, but have voltage autodetect instead. These systems check the
VOLDET pin (pin S4) on the microprocessor when the system is powered on.
■ The VOLDET pin is tied to ground (Vss) internally to the microprocessor. If you cannot
find any jumpers for setting voltage, you can check the motherboard as follows: Switch the
PC off, remove the microprocessor, connect pin S4 to a Vss pin on the ZIF socket, power
on, and check any Vcc pin with a voltmeter. This should read 3.45 (± 0.15) volts. See the
previous section on CPU sockets for the pinout.
■ The 5x86 requires a 33MHz motherboard speed, so be sure the board is set to that frequency. The 5x86 operates at an internal speed of 133MHz. Therefore, the jumpers must be
set for “clock-quadrupled” or “4x clock” mode. By setting the jumpers correctly on the
motherboard, the CLKMUL pin (pin R17) on the processor will be connected to ground
(Vss). If there is no 4x clock setting, the standard DX2 2x clock setting should work.
■ Some motherboards have jumpers that configure the internal cache in either write-back
(WB) or write-through (WT) mode. They do this by pulling the WB/WT pin (pin B13) on
the microprocessor to logic High (Vcc) for WB or to ground (Vss) for WT. For best performance, configure your system in WB mode; however, reset the cache to WT mode if there
are problems running applications or the floppy drive doesn’t work right (DMA conflicts).
■ The 5x86 runs hot, so a heat sink is required; it normally must have a fan.
In addition to the 5x86, the AMD enhanced 486 product line includes 80MHz, 100MHz, and
1,20MHz CPUs. These are the A80486DX2-80SV8B (40MHz×2), A80486DX4-100SV8B (33MHz×3),
and the A80486DX4–120SV8B (40MHz×3).
Cyrix/TI 486
The Cyrix 486DX2/DX4 processors were available in 100MHz, 80MHz, 75MHz, 66MHz, and
50MHz versions. Like the AMD 486 chips, the Cyrix versions are fully compatible with Intel’s 486
processors and work in most 486 motherboards.
The Cx486DX2/DX4 incorporates an 8KB write-back cache, an integrated floating-point unit,
advanced power management, and SMM, and was available in 3.3v versions.
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Chapter 3
Note
TI originally made all the Cyrix-designed 486 processors, and under their agreement they also sold them under the
TI name. Eventually, TI and Cyrix had a falling out, and now IBM makes most of the Cyrix chips, although that
might change since National Semiconductor has purchased Cyrix, and is now attempting to sell it.
P5 (586) Fifth-Generation Processors
Pentium Processors
On October 19, 1992, Intel announced that the fifth generation of its compatible microprocessor
line (code-named P5) would be named the Pentium processor rather than the 586, as everybody
had been assuming. Calling the new chip the 586 would have been natural, but Intel discovered
that it could not trademark a number designation, and the company wanted to prevent other
manufacturers from using the same name for any clone chips that they might develop. The
actual Pentium chip shipped on March 22, 1993. Systems that use these chips were only a few
months behind.
The Pentium is fully compatible with previous Intel processors, but it also differs from them in
many ways. At least one of these differences is revolutionary: The Pentium features twin data
pipelines, which enable it to execute two instructions at the same time. The 486 and all preceding chips can perform only a single instruction at a time. Intel calls the capability to execute two
instructions at the same time superscalar technology. This technology provides additional performance compared with the 486.
The standard 486 chip can execute a single instruction in an average of two clock cycles—cut to
an average of one clock cycle with the advent of internal clock multiplication used in the DX2
and DX4 processors. With superscalar technology, the Pentium can execute many instructions at
a rate of two instructions per cycle. Superscalar architecture usually is associated with high-output
RISC (Reduced Instruction Set Computer) chips. The Pentium is one of the first CISC (Complex
Instruction Set Computer) chips to be considered superscalar. The Pentium is almost like having
two 486 chips under the hood. Table 3.20 shows the Pentium processor specifications.
Table 3.20
Pentium Processor Specifications
Introduced
March 22, 1993 (first generation); March 7, 1994 (second generation)
Maximum rated speeds
60, 66, 75, 90, 100, 120, 133, 150, 166, 200MHz (second generation)
CPU clock multiplier
1x (first generation), 1.5x–3x (second generation)
Register size
32-bit
External data bus
64-bit
Memory address bus
32-bit
Maximum memory
4GB
Integral-cache size
8KB code, 8KB data
Integral-cache type
Two-way set associative, write-back Data
Burst-mode transfers
Yes
(continues)
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Continued
Number of transistors
3.1 million
Circuit size
0.8 micron (60/66MHz), 0.6 micron (75–100MHz), 0.35 micron (120MHz
and up)
External package
273-pin PGA, 296-pin SPGA, tape carrier
Math coprocessor
Built-in FPU (floating-point unit)
Power management
SMM (system management mode), enhanced in second generation
Operating voltage
5v (first generation), 3.465v, 3.3v, 3.1v, 2.9v (second generation)
PGA = Pin Grid Array
SPGA = Staggered Pin Grid Array
The two instruction pipelines within the chip are called the u- and v-pipes. The u-pipe, which is
the primary pipe, can execute all integer and floating-point instructions. The v-pipe is a secondary
pipe that can execute only simple integer instructions and certain floating-point instructions. The
process of operating on two instructions simultaneously in the different pipes is called pairing.
Not all sequentially executing instructions can be paired, and when pairing is not possible, only
the u-pipe is used. To optimize the Pentium’s efficiency, you can recompile software to allow
more instructions to be paired.
The Pentium is 100 percent software-compatible with the 386 and 486, and although all current
software will run much faster on the Pentium, many software manufacturers want to recompile
their applications to exploit even more of the Pentium’s true power. Intel has developed new
compilers that will take full advantage of the chip; the company will license the technology to
compiler firms so that software developers can take advantage of the Pentium’s superscalar (parallel processing) capability. This optimization rapidly started to appear in the software on the market. Optimized software improved performance by allowing more instructions to execute
simultaneously in both pipes.
The Pentium processor has a Branch Target Buffer (BTB), which employs a technique called
branch prediction. It minimizes stalls in one or more of the pipes caused by delays in fetching
instructions that branch to nonlinear memory locations. The BTB attempts to predict whether a
program branch will be taken, and then fetches the appropriate instructions. The use of branch
prediction enables the Pentium to keep both pipelines operating at full speed. Figure 3.33 shows
the internal architecture of the Pentium processor.
The Pentium has a 32-bit address bus width, giving it the same 4GB memory-addressing capabilities as the 386DX and 486 processors. But the Pentium expands the data bus to 64 bits, which
means that it can move twice as much data into or out of the CPU, compared with a 486 of the
same clock speed. The 64-bit data bus requires that system memory be accessed 64 bits wide,
which means that each bank of memory is 64 bits.
On most motherboards, memory is installed via SIMMs (Single Inline Memory Modules) or
DIMMs (Dual Inline Memory Modules). SIMMs are available in 8-bit-wide and 32-bit-wide versions, while DIMMs are 64 bits wide. There are also versions with additional bits for parity or
ECC (error correcting code) data. Most Pentium systems use the 32-bit-wide SIMMs—two of these
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131
SIMMs per bank of memory. Most Pentium motherboards have at least four of these 32-bit SIMM
sockets, providing for a total of two banks of memory. The newest Pentium systems and most
Pentium II systems today use DIMMs, which are 64 bits wide—just like the processor’s external
data bus so only one DIMM is used per bank. This makes installing or upgrading memory much
easier because DIMMs can go in one at a time and don’t have to be matched up in pairs.
Control
DP
Logic
Branch Prefetch TLB
Code Cache
Target
8 KBytes
Buffer Address
256
Instruction
Pointer
64-Bit
Data
Bus
32-Bit
Address
Bus
Control
ROM
Prefetch Buffers
Instruction Decode
Branch Verif.
& Target Addr
Bus
Unit
Control Unit
Page
Unit
Address
Generate
(U Pipeline)
Control
Address
Generate
(V Pipeline)
Floating
Point
Unit
Control
Register File
Integer Register File
64-Bit 64
Data
Bus
ALU
(U Pipeline)
Divide
Barrel Shifter
Control
Figure 3.33
80
Multiply
80
32
32
APIC
Add
32
32-Bit
Addr.
Bus
Data
ALU
(V Pipeline)
32
TLB
Data Cache
8 KBytes
32
32
32
Pentium processor internal architecture.
◊◊ See “SIMMs and DIMMs,” p. 437, and “Memory Banks,” p. 451.
Even though the Pentium has a 64-bit data bus that transfers information 64 bits at a time into
and out of the processor, the Pentium has only 32-bit internal registers. As instructions are being
processed internally, they are broken down into 32-bit instructions and data elements, and
processed in much the same way as in the 486. Some people thought that Intel was misleading
them by calling the Pentium a 64-bit processor, but 64-bit transfers do indeed take place.
Internally, however, the Pentium has 32-bit registers that are fully compatible with the 486.
The Pentium has two separate internal 8KB caches, compared with a single 8KB or 16KB cache in
the 486. The cache-controller circuitry and the cache memory are embedded in the CPU chip.
The cache mirrors the information in normal RAM by keeping a copy of the data and code from
different memory locations. The Pentium cache also can hold information to be written to
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memory when the load on the CPU and other system components is less. (The 486 makes all
memory writes immediately.)
The separate code and data caches are organized in a two-way set associative fashion, with each
set split into lines of 32 bytes each. Each cache has a dedicated Translation Lookaside Buffer (TLB)
that translates linear addresses to physical addresses. You can configure the data cache as writeback or write-through on a line-by-line basis. When you use the write-back capability, the cache
can store write operations and reads, further improving performance over read-only writethrough mode. Using write-back mode results in less activity between the CPU and system memory—an important improvement, because CPU access to system memory is a bottleneck on fast
systems. The code cache is an inherently write-protected cache because it contains only execution instructions and not data, which is updated. Because burst cycles are used, the cache data
can be read or written very quickly.
Systems based on the Pentium can benefit greatly from secondary processor caches (L2), which
usually consist of up to 512KB or more of extremely fast (15ns or less) Static RAM (SRAM) chips.
When the CPU fetches data that is not already available in its internal processor (L1) cache, wait
states slow the CPU. If the data already is in the secondary processor cache, however, the CPU
can go ahead with its work without pausing for wait states.
The Pentium uses a BiCMOS (bipolar complementary metal oxide semiconductor) process and
superscalar architecture to achieve the high level of performance expected from the chip.
BiCMOS adds about 10 percent to the complexity of the chip design, but adds about 30–35 percent better performance without a size or power penalty.
All Pentium processors are SL enhanced, meaning that they incorporate the SMM to provide full
control of power-management features, which helps reduce power consumption. The
second-generation Pentium processors (75MHz and faster) incorporate a more advanced form of
SMM that includes processor clock control. This allows you to throttle the processor up or down
to control power use. You can even stop the clock with these more advanced Pentium processors,
putting the processor in a state of suspension that requires very little power. The second-generation Pentium processors run on 3.3v power (instead of 5v), reducing power requirements and
heat generation even further.
Many current motherboards supply either 3.465v or 3.3v. The 3.465v setting is called VRE
(Voltage Reduced Extended) by Intel and is required by some versions of the Pentium, particularly some of the 100MHz versions. The standard 3.3v setting is called STD (Standard), which
most of the second-generation Pentiums use. STD voltage means anything in a range from 3.135v
to 3.465v with 3.3v nominal. There is also a special 3.3v setting called VR (Voltage Reduced),
which reduces the range from 3.300v to 3.465v with 3.38v nominal. Some of the processors
require this narrower specification, which most motherboards provide. Here is a summary:
Voltage
Specification
Nominal
Tolerance
Minimum
Maximum
STD (Standard)
3.30v
±0.165
3.135v
3.465v
VR (Voltage Reduced)
3.38v
±0.083
3.300v
3.465v
VRE (VR Extended)
3.50v
±0.100
3.400v
3.600v
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For even lower power consumption, Intel introduced special Pentium processors with Voltage
Reduction Technology in the 75 to 266MHz family; the processors are intended for mobile computer applications. They do not use a conventional chip package and are instead mounted using
a new format called tape carrier packaging (TCP). The tape carrier packaging does not encase the
chip in ceramic or plastic as with a conventional chip package, but instead covers the actual
processor die directly with a thin, protective plastic coating. The entire processor is less than
1mm thick, or about half the thickness of a dime, and weighs less than 1 gram. They are sold to
system manufacturers in a roll that looks very much like a filmstrip. The TCP processor is directly
affixed (soldered) to the motherboard by a special machine, resulting in a smaller package, lower
height, better thermal transfer, and lower power consumption. Special solder plugs on the circuit
board located directly under the processor draw heat away and provide better cooling in the tight
confines of a typical notebook or laptop system—no cooling fans are required. For more information on mobile processors and systems, see Chapter 23, “Portable PCs.”
The Pentium, like the 486, contains an internal math coprocessor or FPU. The FPU in the
Pentium has been rewritten and performs significantly better than the FPU in the 486, yet it is
fully compatible with the 486 and 387 math coprocessor. The Pentium FPU is estimated at two to
as much as 10 times faster than the FPU in the 486. In addition, the two standard instruction
pipelines in the Pentium provide two units to handle standard integer math. (The math coprocessor handles only more complex calculations.) Other processors, such as the 486, have only a single-standard execution pipe and one integer math unit. Interestingly, the Pentium FPU contains a
flaw that received widespread publicity. See the discussion in the section “Pentium Defects,” later
in this chapter.
First-Generation Pentium Processor
The Pentium has been offered in three basic designs, each with several versions. The
first-generation design, which is no longer available, came in 60 and 66MHz processor speeds.
This design used a 273-pin PGA form factor and ran on 5v power. In this design, the processor
ran at the same speed as the motherboard—in other words, a 1x clock is used.
The first-generation Pentium was created through an 0.8 micron BiCMOS process. Unfortunately,
this process, combined with the 3.1 million transistor count, resulted in a die that was overly
large and complicated to manufacture. As a result, reduced yields kept the chip in short supply;
Intel could not make them fast enough. The 0.8 micron process was criticized by other manufacturers, including Motorola and IBM, which had been using 0.6 micron technology for their most
advanced chips. The huge die and 5v operating voltage caused the 66MHz versions to consume
up to an incredible 3.2 amps or 16 watts of power, resulting in a tremendous amount of heat and
problems in some systems that did not employ conservative design techniques. Fortunately,
adding a fan to the processor would solve most cooling problems, as long as the fan kept running.
Much of the criticism leveled at Intel for the first-generation Pentium was justified. Some people
realized that the first-generation design was just that; they knew that new Pentium versions,
made in a more advanced manufacturing process, were coming. Many of those people advised
against purchasing any Pentium system until the second-generation version became available.
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Tip
A cardinal rule of computing is never buy the first generation of any processor. Although you can wait forever
because something better always will be on the horizon, a little waiting is worthwhile in some cases.
If you do have one of these first-generation Pentiums, do not despair. As with previous 486 systems, Intel offers OverDrive upgrade chips that effectively double the processor speed of your
Pentium 60 or 66. These are a single-chip upgrade, meaning they replace your existing CPU.
Because subsequent Pentiums are incompatible with the Pentium 60/66 Socket 4 arrangement,
these OverDrive chips were the only way to upgrade an existing first-generation Pentium without
replacing the motherboard.
Rather than upgrading the processor with one only twice as fast, you should really consider a
complete motherboard replacement, which would accept a newer design processor that would
potentially be many times faster.
Second-Generation Pentium Processor
Intel announced the second-generation Pentium on March 7, 1994. This new processor was introduced in 90 and 100MHz versions, with a 75MHz version not far behind. Eventually, 120, 133,
150, 166, and 200MHz versions were also introduced. The second-generation Pentium uses 0.6
micron (75/90/100MHz) BiCMOS technology to shrink the die and reduce power consumption.
The newer, faster 120MHz (and higher) second-generation versions incorporate an even smaller
die built on a 0.35 micron BiCMOS process. These smaller dies are not changed from the 0.6
micron versions; they are basically a photographic reduction of the P54C die. The die for the
Pentium is shown in Figure 3.34. Additionally, these new processors run on 3.3v power. The
100MHz version consumes a maximum 3.25 amps of 3.3v power, which equals only 10.725
watts. Further up the scale, the 150MHz chip uses 3.5 amps of 3.3v power (11.6 watts); the
166MHz unit draws 4.4 amps (14.5 watts); and the 200MHz processor uses 4.7 amps (15.5 watts).
The second-generation Pentium processors come in a 296-pin SPGA form factor that is physically
incompatible with the first-generation versions. The only way to upgrade from the first generation to the second is to replace the motherboard. The second-generation Pentium processors also
have 3.3 million transistors—more than the earlier chips. The extra transistors exist because additional clock-control SL enhancements were added, along with an on-chip Advanced
Programmable Interrupt Controller (APIC) and dual-processor interface.
The APIC and dual-processor interface are responsible for orchestrating dual-processor configurations in which two second-generation Pentium chips can process on the same motherboard
simultaneously. Many of the Pentium motherboards designed for file servers come with dual
Socket 7 specification sockets, which fully support the multiprocessing capability of the new
chips. Software support for what usually is called Symmetric Multi-Processing (SMP) is being
integrated into operating systems such as Windows NT and OS/2.
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Figure 3.34
135
Chapter 3
Pentium processor die. Photograph used by permission of Intel Corporation.
The second-generation Pentium processors use clock-multiplier circuitry to run the processor at
speeds faster than the bus. The 150MHz Pentium processor, for example, can run at 2.5 times the
bus frequency, which normally is 60MHz. The 200MHz Pentium processor can run at a 3x clock
in a system using a 66MHz bus speed.
Note
Some Pentium systems support 75MHz or even up to 100MHz with newer motherboard and chipset designs.
Virtually all Pentium motherboards have three speed settings: 50, 60, and 66MHz. Pentium chips
are available with a variety of internal clock multipliers that cause the processor to operate at various multiples of these motherboard speeds. Table 3.21 lists the speeds of currently available
Pentium processors and motherboards.
Table 3.21
Pentium CPU and Motherboard Speeds
CPU Type/Speed
CPU Clock
Motherboard Speed (MHz)
Pentium 75
1.5x
50
Pentium 90
1.5x
60
Pentium 100
1.5x
66
Pentium 120
2x
60
Pentium 133
2x
66
(continues)
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Continued
CPU Type/Speed
CPU Clock
Motherboard Speed (MHz)
Pentium 150
2.5x
60
Pentium 166
2.5x
66
Pentium 200
3x
66
Pentium 233
3.5x
66
Pentium 266
4x
66
The core-to-bus frequency ratio or clock multiplier is controlled in a Pentium processor by two
pins on the chip labeled BF1 and BF2. Table 3.22 shows how the state of the BFx pins will affect
the clock multiplication in the Pentium processor.
Table 3.22
Pentium BFx Pins and Clock Multipliers
BF1
BF2
Clock
Multiplier
Bus Speed
(MHz)
Core Speed
(MHz)
0
1
3x
66
200
0
1
3x
60
180
0
1
3x
50
150
0
0
2.5x
66
166
0
0
2.5x
60
150
0
0
2.5x
50
125
1
0
2x/4x
66
133/266*
1
0
2x
60
120
1
0
2x
50
100
1
1
1.5x/3.5x
66
100/233*
1
1
1.5x
60
90
1
1
1.5x
50
75
*The 233 and 266MHz processors have modified the 1.5x and 2x multipliers to 3.5x and 4x, respectively.
Not all chips support all the bus frequency (BF) pins or combinations of settings. In other words,
some of the Pentium processors will operate only at specific combinations of these settings, or
may even be fixed at one particular setting. Many of the newer motherboards have jumpers or
switches that allow you to control the BF pins and, therefore, alter the clock multiplier ratio
within the chip. In theory, you could run a 75MHz-rated Pentium chip at 133MHz by changing
jumpers on the motherboard. This is called overclocking, and is discussed in the “Processor Speed
Ratings” section of this chapter. What Intel has done to discourage overclockers in its most recent
Pentiums is discussed near the end of the “Processor Manufacturing” section of this chapter.
A single-chip OverDrive upgrade is currently offered for second-generation Pentiums. These
OverDrive chips are fixed at a 3x multiplier; they replace the existing Socket 5 or 7 CPU, increase
processor speed up to 200MHz (with a 66MHz motherboard speed), and add MMX capability, as
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well. Simply stated, this means that a Pentium 100, 133, or 166 system equipped with the
OverDrive chip will have a processor speed of 200MHz. Perhaps the best feature of these Pentium
OverDrive chips is that they incorporate MMX technology. MMX provides greatly enhanced performance while running the multimedia applications that are so popular today.
If you have a Socket 7 motherboard, you might not need the special OverDrive versions of the
Pentium processor that have built-in voltage regulators. Instead, you can purchase a standard
Pentium or Pentium-compatible chip and replace the existing processor with it. You will have to
be sure to set the multiplier and voltage settings so that they are correct for the new processor.
Pentium-MMX Processors
A third generation of Pentium processors (code-named P55C) was released in January 1997,
which incorporates what Intel calls MMX technology into the second-generation Pentium design
(see Figure 3.35). These Pentium-MMX processors are available in clock rates of 66/166MHz,
66/200MHz, and 66/233MHz, and a mobile-only version, which is 66/266MHz. The MMX processors have a lot in common with other second-generation Pentiums, including superscalar architecture, multiprocessor support, on-chip local APIC controller, and power-management features.
New features include a pipelined MMX unit, 16KB code, write-back cache (versus 8KB in earlier
Pentiums), and 4.5 million transistors. Pentium-MMX chips are produced on an enhanced 0.35
micron CMOS silicon process that allows for a lower 2.8v voltage level. The newer mobile
233MHz and 266MHz processors are built on a 0.25 micron process and run on only 1.8 volts.
With this newer technology, the 266 processor actually uses less power than the non-MMX 133.
Figure 3.35 Pentium MMX. The left side shows the underside of the chip with the cover plate
removed exposing the processor die. Photograph used by permission of Intel Corporation.
To use the Pentium-MMX, the motherboard must be capable of supplying the lower (2.8v or less)
voltage these processors use. To allow a more universal motherboard solution with respect to
these changing voltages, Intel has come up with the Socket 7 with VRM. The VRM is a socketed
module that plugs in next to the processor and supplies the correct voltage. Because the module
is easily replaced, it is easy to reconfigure a motherboard to support any of the voltages required
by the newer Pentium processors.
Of course, lower voltage is nice, but MMX is what this chip is really all about. MMX technology
was developed by Intel as a direct response to the growing importance and increasing demands of
multimedia and communication applications. Many such applications run repetitive loops of
instructions that take vast amounts of time to execute. As a result, MMX incorporates a process
Intel calls Single Instruction Multiple Data (SIMD), which allows one instruction to perform the
same function on many pieces of data. Furthermore, 57 new instructions that are designed specifically to handle video, audio, and graphics data have been added to the chip.
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If you want maximum future upgradability to the MMX Pentiums, make sure that your Pentium
motherboard includes 321-pin processor sockets that fully meet the Intel Socket 7 specification.
These would also include the VRM (Voltage Regulator Module) socket. If you have dual sockets,
you can add a second Pentium processor to take advantage of SMP (Symmetric Multiprocessing)
support in some newer operating systems.
Also make sure that any Pentium motherboard you buy can be jumpered or reconfigured for both
60 and 66MHz operation. This will enable you to take advantage of future Pentium OverDrive
processors that will support the higher motherboard clock speeds. These simple recommendations will enable you to perform several dramatic upgrades without changing the entire motherboard.
Pentium Defects
Probably the most famous processor bug in history is the now legendary flaw in the Pentium
FPU. It has often been called the FDIV bug, because it affects primarily the FDIV (floating-point
divide) instruction, although several other instructions that use division are also affected. Intel
officially refers to this problem as Errata No. 23, titled “Slight precision loss for floating-point
divides on specific operand pairs.” The bug has been fixed in the D1 or later steppings of the
60/66MHz Pentium processors, as well as the B5 and later steppings of the 75/90/100MHz processors. The 120MHz and higher processors are manufactured from later steppings, which do not
include this problem. There are tables listing all the different variations of Pentium processors
and steppings and how to identify them later in this chapter.
This bug caused a tremendous fervor when it first was reported on the Internet by a mathematician in October, 1994. Within a few days, news of the defect had spread nationwide, and even
people who did not have computers had heard about it. The Pentium would incorrectly perform
floating-point division calculations with certain number combinations, with errors anywhere
from the third digit on up.
By the time the bug was publicly discovered outside of Intel, they had already incorporated the
fix into the next stepping of both the 60/66MHz and the 75/90/100MHz Pentium processor,
along with the other corrections they had made.
After the bug was made public and Intel admitted to already knowing about it, a fury erupted. As
people began checking their spreadsheets and other math calculations, many discovered that
they had also encountered this problem and did not know it. Others who had not encountered
the problem had their faith in the core of their PCs very shaken. People had come to put so
much trust in the PC that they had a hard time coming to terms with the fact that it might not
even be capable of doing math correctly!
One interesting result of the fervor surrounding this defect is that people are less likely to implicitly trust their PCs, and are therefore doing more testing and evaluating of important results. The
bottom line is that if your information and calculations are important enough, you should implement some results tests. Several math programs were found to have problems. For example, a bug
was discovered in the yield function of Excel 5.0 that some were attributing to the Pentium
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processor. In this case, the problem turned out to be the software, which has been corrected in
later versions (5.0c and later).
Intel finally decided that in the best interest of the consumer and their public image, they would
begin a lifetime replacement warranty on the affected processors. This means that if you ever
encounter one of the Pentium processors with the Errata 23 floating-point bug, they will replace
the processor with an equivalent one without this problem. Normally, all you have to do is call
Intel and ask for the replacement. They will ship you a new part matching the ratings of the one
you are replacing in an overnight shipping box. The replacement is free, including all shipping
charges. You merely remove your old processor, replace it with the new one, and put the old one
back in the box. Then you call the overnight service who will pick it up and send it back. Intel
will take a credit card number when you first call for the replacement only to ensure that the
original defective chip is returned. As long as they get the original CPU back within a specified
amount of time, there will be no charges to you. Intel has indicated that these defective processors will be destroyed and will not be remarketed or resold in another form.
Testing for the FPU Bug
Testing a Pentium for this bug is relatively easy. All you have to do is execute one of the test division cases cited here and see if your answer compares to the correct result.
The division calculation can be done in a spreadsheet (such as Lotus 1-2-3, Microsoft Excel, or
any other), in the Microsoft Windows built-in calculator, or in any other calculating program
that uses the FPU. Make sure that for the purposes of this test the FPU has not been disabled.
That would normally require some special command or setting specific to the application, and
would, of course, ensure that the test came out correct, no matter whether the chip is flawed or
not.
The most severe Pentium floating-point errors occur as early as the third significant digit of the
result. Here is an example of one of the more severe instances of the problem:
962,306,957,033 / 11,010,046 = 87,402.6282027341 (correct answer)
962,306,957,033 / 11,010,046 = 87,399.5805831329 (flawed Pentium)
Note
Note that your particular calculator program may not show the answer to the number of digits shown here. Most
spreadsheet programs limit displayed results to 13 or 15 significant digits.
As you can see in the previous case, the error turns up in the third most significant digit of the
result. In an examination of over 5,000 integer pairs in the 5- to 15-digit range found to produce
Pentium floating-point division errors, errors beginning in the sixth significant digit were the
most likely to occur.
Here is another division problem that will come out incorrectly on a Pentium with this flaw:
4,195,835 / 3,145,727 = 1.33382044913624100 (correct answer)
4,195,835 / 3,145,727 = 1.33373906890203759 (flawed Pentium)
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This one shows an error in the fifth significant digit. A variation on the previous calculation can
be performed as follows:
x = 4,195,835
y = 3,145,727
z = x – (x/y) × y
4,195,835 – (4,195,835 / 3,145,727) × 3,145,727 = 0 (correct answer)
4,195,835 – (4,195,835 / 3,145,727) × 3,145,727 = 256 (flawed Pentium)
With an exact computation, the answer here should be zero. In fact, you will get zero on most
machines, including those using Intel 286, 386, and 486 chips. But, on the Pentium, the answer
is 256!
Here is one more calculation you can try:
5,505,001 / 294,911 = 18.66665197 (correct answer)
5,505,001 / 294,911 = 18.66600093 (flawed Pentium)
This one represents an error in the sixth significant digit.
There are several workarounds for this bug, but they extract a performance penalty. Because Intel
has agreed to replace any Pentium processor with this flaw under a lifetime warranty replacement
program, the best workaround is a free replacement!
Power Management Bugs
Starting with the second-generation Pentium processors, Intel added functions that allow these
CPUs to be installed in energy-efficient systems. These are usually called Energy Star systems
because they meet the specifications imposed by the EPA Energy Star program, but they are also
unofficially called green PCs by many users.
Unfortunately, there have been several bugs with respect to these functions, causing them to
either fail or be disabled. These bugs are in some of the functions in the power-management
capabilities accessed through SMM. These problems are applicable only to the second-generation
75/90/100MHz processors, because the first-generation 60/66MHz processors do not have SMM or
power-management capabilities, and all higher speed (120MHz and up) processors have the bugs
fixed.
Most of the problems are related to the STPCLK# pin and the HALT instruction. If this condition
is invoked by the chipset, the system will hang. For most systems, the only workaround for this
problem is to disable the power-saving modes, such as suspend or sleep. Unfortunately, this
means that your green PC won’t be so green anymore! The best way to repair the problem is to
replace the processor with a later stepping version that does not have the bug. These bugs affect
the B1 stepping version of the 75/90/100MHz Pentiums, and were fixed in the B3 and later stepping versions.
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Pentium Processor Models and Steppings
We know that like software, no processor is truly ever perfect. From time to time, the manufacturers will gather up what problems they have found and put into production a new stepping,
which consists of a new set of masks that incorporate the corrections. Each subsequent stepping
is better and more refined than the previous ones. Although no microprocessor is ever perfect,
they come closer to perfection with each stepping. In the life of a typical microprocessor, a manufacturer may go through half a dozen or more such steppings.
Table 3.23 shows all the versions of the Pentium processor Model 1 (60/66MHz version), indicating the various steppings that have been available.
Table 3.23
Pentium Processor Model 1 (60/66MHz Version) Steppings
Type
Family
Model
Stepping
Mfg.
Stepping
Speed
Comments
Specification
Number
0
5
1
3
B1
50
Q0399
ES
0
5
1
3
B1
60
Q0352
0
5
1
3
B1
60
Q0400
ES
0
5
1
3
B1
60
Q0394
ES, HS
0
5
1
3
B1
66
Q0353
5v1
0
5
1
3
B1
66
Q0395
ES, HS, 5v1
0
5
1
3
B1
60
Q0412
0
5
1
3
B1
60
SX753
0
5
1
3
B1
66
Q0413
5v2
0
5
1
3
B1
66
SX754
5v2
0
5
1
5
C1
60
Q0466
HS
0
5
1
5
C1
60
SX835
HS
0
5
1
5
C1
60
SZ949
HS, BOX
0
5
1
5
C1
66
Q0467
HS, 5v2
0
5
1
5
C1
66
SX837
HS, 5v2
0
5
1
5
C1
66
SZ950
HS, BOX, 5v2
0
5
1
7
D1
60
Q0625
HS
0
5
1
7
D1
60
SX948
HS
0
5
1
7
D1
60
SX974
HS, 5v3
0
5
1
7
D1
60
—*
HS, BOX
0
5
1
7
D1
66
Q0626
HS, 5v2
0
5
1
7
D1
66
SX950
HS, 5v2
0
5
1
7
D1
66
Q0627
HS, 5v3
0
5
1
7
D1
66
SX949
HS, 5v3
0
5
1
7
D1
66
—*
HS, BOX, 5v2
Tables 3.24, 3.25, 3.26, and 3.28 show all the different variations of Pentium
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75/90/100/120/133/150/166/200/233/266MHz, classic and MMX processors. Table 3.24 lists classic (non-MMX) desktop models. Table 3.25 lists MMX desktop models. Explanations of all the
specifications and the comments in the comments column follow Table 3.26, the listing of
Pentium OverDrive models.
Table 3.24
Pentium Processor Versions and Steppings
Type
Family
Model
Stepping
Core
Stepping
Speed (MHz)
Core-Bus
S-Spec
Comments
0
5
2
1
B1
75-50
Q0540
ES
2
5
2
1
B1
75-50
Q0541
ES
0
5
2
1
B1
90-60
Q0542
STD
0
5
2
1
B1
90-60
Q0613
VR
2
5
2
1
B1
90-60
Q0543
DP
0
5
2
1
B1
100-66
Q0563
STD
0
5
2
1
B1
100-66
Q0587
VR
0
5
2
1
B1
100-66
Q0614
VR
0
5
2
1
B1
90-60
SX879
STD
0
5
2
1
B1
90-60
SX885
STD, MD
0
5
2
1
B1
90-60
SX909
VR
2
5
2
1
B1
90-60
SX874
DP, STD
0
5
2
1
B1
100-66
SX886
STD, MD
0
5
2
1
B1
100-66
SX910
VR, MD
0
5
2
2
B3
90-60
Q0628
STD
0/2
5
2
2
B3
90-60
Q0611
STD
0/2
5
2
2
B3
90-60
Q0612
VR
0
5
2
2
B3
100-66
Q0677
VRE
0
5
2
2
B3
90-60
SX923
STD
0
5
2
2
B3
90-60
SX922
VR
0
5
2
2
B3
90-60
SX921
STD
2
5
2
2
B3
90-60
SX942
DP, STD
2
5
2
2
B3
90-60
SX943
DP, VR
2
5
2
2
B3
90-60
SX944
DP, MD
0
5
2
2
B3
90-60
SZ951
BOX, STD
0
5
2
2
B3
100-66
SX960
VRE, MD
0/2
5
2
4
B5
75-50
Q0666
STD
0/2
5
2
4
B5
90-60
Q0653
STD
0/2
5
2
4
B5
90-60
Q0654
VR
0/2
5
2
4
B5
90-60
Q0655
STD, MD
0/2
5
2
4
B5
100-66
Q0656
STD, MD
0/2
5
2
4
B5
100-66
Q0657
VR, MD
0/2
5
2
4
B5
100-66
Q0658
VRE, MD
0
5
2
4
B5
120-60
Q0707
VRE
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Type
Family
Model
Stepping
Core
Stepping
Speed (MHz)
Core-Bus
S-Spec
0
5
2
4
B5
120-60
Q0708
STD
0/2
5
2
4
B5
75-50
SX961
STD
0/2
5
2
4
B5
75-50
SZ977
BOX, STD
0/2
5
2
4
B5
90-60
SX957
STD
0/2
5
2
4
B5
90-60
SX958
VR
0/2
5
2
4
B5
90-60
SX959
STD, MD
0/2
5
2
4
B5
90-60
SZ978
BOX, STD
0/2
5
2
4
B5
100-66
SX962
VRE, MD
0/2
5
2
5
C2
75-50
Q0700
STD
0/2
5
2
5
C2
75-50
Q0749
STD, MD
0/2
5
2
5
C2
90-60
Q0699
STD
0/2
5
2
5
C2
100-50/66
Q0698
VRE, MD
Comments
0/2
5
2
5
C2
100-50/66
Q0697
STD
0
5
2
5
C2
120-60
Q0711
VRE, MD
0
5
2
5
C2
120-60
Q0732
VRE, MD
0
5
2
5
C2
133-66
Q0733
STD, MD
0
5
2
5
C2
133-66
Q0751
STD, MD
0
5
2
5
C2
133-66
Q0775
VRE, MD
0/2
5
2
5
C2
75-50
SX969
STD
0/2
5
2
5
C2
75-50
SX998
STD, MD
0/2
5
2
5
C2
75-50
SZ994
BOX, STD
0/2
5
2
5
C2
75-50
SU070
BOXF, STD
0/2
5
2
5
C2
90-60
SX968
STD
0/2
5
2
5
C2
90-60
SZ995
BOX, STD
0/2
5
2
5
C2
90-60
SU031
BOXF, STD
0/2
5
2
5
C2
100-50/66
SX970
VRE, MD
0/2
5
2
5
C2
100-50/66
SX963
STD
0/2
5
2
5
C2
100-50/66
SZ996
BOX, STD
0/2
5
2
5
C2
100-50/66
SU032
BOXF, STD
0
5
2
5
C2
120-60
SK086
VRE, MD
0
5
2
5
C2
120-60
SX994
VRE, MD
0
5
2
5
C2
120-60
SU033
BOXF, VRE, MD
0
5
2
5
C2
133-66
SK098
STD, MD
0/2
5
2
B
cB1
120-60
Q0776
STD, No, STP
0/2
5
2
B
cB1
133-66
Q0772
STD, No, STP
0/2
5
2
B
cB1
133-66
Q0773
STD,STP
0/2
MD
5
2
B
cB1
133-66
Q0774
VRE, No, STP,
0/2
5
2
B
cB1
120-60
SK110
STD, No, STP
(continues)
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Microprocessor Types and Specifications
Continued
Type
Family
Model
Stepping
Core
Stepping
Speed (MHz)
Core-Bus
S-Spec
Comments
0/2
5
2
B
cB1
133-66
SK106
STD, No, STP
0/2
5
2
B
cB1
133-66
S106J
STD, No, STP
0/2
5
2
B
cB1
133-66
SK107
STD, STP
0/2
5
2
B
cB1
133-66
SU038
BOXF, STD, No,
STP
0/2
5
2
C
cC0
133-66
Q0843
STD, No
0/2
5
2
C
cC0
133-66
Q0844
STD
0/2
5
2
C
cC0
150-60
Q0835
STD
0/2
5
2
C
cC0
150-60
Q0878
STD, PPGA
0/2
5
2
C
cC0
150-60
SU122
BOXF, STD
0/2
5
2
C
cC0
166-66
Q0836
VRE, No
0/2
5
2
C
cC0
166-66
Q0841
VRE
0/2
5
2
C
cC0
166-66
Q0886
VRE, PPGA
0/2
5
2
C
cC0
166-66
Q0890
VRE, PPGA
0
5
2
C
cC0
166-66
Q0949
VRE, PPGA
VRE, PPGA
0/2
5
2
C
cC0
200-66
Q0951F
0
5
2
C
cC0
200-66
Q0951
VRE, PPGA
0
5
2
C
cC0
200-66
SL25H
BOXF, VRE,
PPGA
0/2
5
2
C
cC0
120-60
SL22M
BOXF, STD
0/2
5
2
C
cC0
120-60
SL25J
BOX, STD
0/2
5
2
C
cC0
120-60
SY062
STD
0/2
5
2
C
cC0
133-66
SL22Q
BOXF, STD
0/2
5
2
C
cC0
133-66
SL25L
BOX, STD
0/2
5
2
C
cC0
133-66
SY022
STD
0/2
5
2
C
cC0
133-66
SY023
STD, No
0/2
5
2
C
cC0
133-66
SU073
BOXF, STD, No
0/2
5
2
C
cC0
150-60
SY015
STD
0/2
5
2
C
cC0
150-60
SU071
BOXF, STD
0/2
5
2
C
cC0
166-66
SL24R
VRE, No, MAXF
0/2
5
2
C
cC0
166-66
SY016
VRE, No
0/2
5
2
C
cC0
166-66
SY017
VRE
0/2
5
2
C
cC0
166-66
SU072
BOXF, VRE, No
0
5
2
C
cC0
166-66
SY037
VRE, PPGA
0/2
5
2
C
cC0
200-66
SY044
VRE, PPGA
0
5
2
C
cC0
200-66
SY045
BOXUF, VRE,
PPGA
0
5
2
C
cC0
200-66
SU114
BOX, VRE,
PPGA
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Type
Family
Model
Stepping
Core
Stepping
Speed (MHz)
Core-Bus
S-Spec
Comments
0
5
2
C
cC0
200-66
SL24Q
VRE, PPGA, No,
MAXF
0/2
5
2
6
E0
75-50
Q0837
STD
0/2
5
2
6
E0
90-60
Q0783
STD
0/2
5
2
6
E0
100-50/66
Q0784
STD
0/2
5
2
6
E0
120-60
Q0785
VRE
0/2
5
2
6
E0
75-50
SY005
STD
0/2
5
2
6
E0
75-50
SU097
BOX, STD
0/2
5
2
6
E0
75-50
SU098
BOXF, STD
0/2
5
2
6
E0
90-60
SY006
STD
0/2
5
2
6
E0
100-50/66
SY007
STD
0/2
5
2
6
E0
100-50/66
SU110
BOX, STD
0/2
5
2
6
E0
100-50/66
SU099
BOXF, STD
0/2
5
2
6
E0
120-60
SY033
STD
0/2
5
2
6
E0
120-60
SU100
BOXF, STD
Table 3.25
Pentium MMX Processor Versions and Steppings
Type
Family
Model
Stepping
Core
Stepping
Core Speed
(MHz)
S-Spec
Comments
0/2
5
4
4
xA3
150
Q020
ES, PPGA
0/2
5
4
4
xA3
166
Q019
ES, PPGA
0/2
5
4
4
xA3
200
Q018
ES, PPGA
0/2
5
4
4
xA3
166
SL23T
BOXF, SPGA
0/2
5
4
4
xA3
166
SL23R
BOX, PPGA
0/2
5
4
4
xA3
166
SL25M
BOXF, PPGA
0/2
5
4
4
xA3
166
SY059
PPGA
0/2
5
4
4
xA3
166
SL2HU
BOX, SPGA
0/2
5
4
4
xA3
166
SL239
SPGA
0/2
5
4
4
xA3
166
SL26V
SPGA, MAXF
0/2
5
4
4
xA3
166
SL26H
PPGA, MAXF
0/2
5
4
4
xA3
200
SL26J
BOXUF, PPGA,
MAXF
0/2
5
4
4
xA3
200
SY060
PPGA
0/2
5
4
4
xA3
200
SL26Q
BOX, PPGA,
MAXF
0/2
5
4
4
xA3
200
SL274
BOXF, PPGA,
MAXF
0/2
5
4
4
xA3
200
SL23S
BOX, PPGA
0/2
5
4
4
xA3
200
SL25N
BOXF, PPGA
(continues)
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Microprocessor Types and Specifications
Continued
Type
Family
Model
Stepping
Core
Stepping
Core Speed
(MHz)
S-Spec
Comments
0/2
5
4
3
xB1
166
Q125
ES, PPGA
0/2
5
4
3
xB1
166
Q126
ES, SPGA
0/2
5
4
3
xB1
200
Q124
ES, PPGA
0/2
5
4
3
xB1
233
Q140
ES, PPGA
0/2
5
4
3
xB1
166
SL27H
PPGA
0/2
5
4
3
xB1
166
SL27K
SPGA
0/2
5
4
3
xB1
166
SL2HX
BOX, SPGA
0/2
5
4
3
xB1
166
SL23X
BOXF, SPGA
0/2
5
4
3
xB1
166
SL2FP
BOX, PPGA
0/2
5
4
3
xB1
166
SL23V
BOXF, PPGA
0/2
5
4
3
xB1
200
SL27J
PPGA
0/2
5
4
3
xB1
200
SL2FQ
BOX, PPGA
0/2
5
4
3
xB1
200
SL23W
BOXF, PPGA
0/2
5
4
3
xB1
233
SL27S
PPGA
0/2
5
4
3
xB1
233
SL2BM
BOX, PPGA
0/2
5
4
3
xB1
233
SL293
BOXF, PPGA
0
5
4
3
mxB1
120
Q230
ES, TCP
0
5
4
3
mxB1
133
Q130
ES, TCP
0
5
4
3
mxB1
133
Q129
ES, PPGA
0
5
4
3
mxB1
150
Q116
ES, TCP
0
5
4
3
mxB1
150
Q128
ES, PPGA
0
5
4
3
mxB1
166
Q115
ES, TCP
0
5
4
3
mxB1
166
Q127
ES, PPGA
0
5
4
3
mxB1
200
Q586
PPGA
0
5
4
3
mxB1
133
SL27D
TCP
0
5
4
3
mxB1
133
SL27C
PPGA
0
5
4
3
mxB1
150
SL26U
TCP
0
5
4
3
mxB1
150
SL27B
PPGA
0
5
4
3
mxB1
166
SL26T
TCP
0
5
4
3
mxB1
166
SL27A
PPGA
0
5
4
3
mxB1
200
SL2WK
PPGA
0
5
8
1
myA0
166
Q255
TCP
0
5
8
1
myA0
166
Q252
TCP
0
5
8
1
myA0
166
SL2N6
TCP
0
5
8
1
myA0
200
Q146
TCP
0
5
8
1
myA0
233
Q147
TCP
0
5
8
1
myA0
200
SL28P
TCP
0
5
8
1
myA0
233
SL28Q
TCP
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Type
Family
Model
Stepping
Core
Stepping
Core Speed
(MHz)
S-Spec
Comments
0
5
8
1
myA0
266
Q250
TCP
0
5
8
1
myA0
266
Q251
TCP
0
5
8
1
myA0
266
SL2N5
TCP
0
5
8
1
myA0
266
Q695
TCP
0
5
8
1
myA0
266
SL2ZH
TCP
0
5
8
2
myB2
266
Q766
TCP
0
5
8
2
myB2
266
Q767
TCP
0
5
8
2
myB2
266
SL23M
TCP
0
5
8
2
myB2
266
SL23P
TCP
0
5
8
2
myB2
300
Q768
TCP
0
5
8
2
myB2
300
SL34N
TCP
147
All the Pentium MMX processors listed in this table run on a 66MHz bus except for 150MHz models, which run
on a 60MHz bus.
Table 3.26 shows all the versions of the Pentium OverDrive processors, indicating the various
steppings that have been available. Note that the Type 1 chips in this table are 486 Pentium
OverDrive processors, which are designed to replace 486 chips in systems with Socket 2 or 3. The
other OverDrive processors are designed to replace existing Pentium processors in Socket 4 or 5/7.
Table 3.26
Pentium OverDrive Steppings
Type
Family
Model
Stepping
Mfg.
Stepping
Speed
Spec.
Number
Product
Version
1
5
3
1
B1
63
SZ953
PODP5v63
1.0
1
5
3
1
B2
63
SZ990
PODP5v63
1.1
1
5
3
2
C0
83
SU014
PODP5v83
2.1
0
5
1
A
tA0
133
SU082
PODP5v133
1.0
0
5
2
C
aC0
125
SU081
PODP3v125
1.0
0
5
2
C
aC0
150
SU083
PODP3v150
1.0
0
5
2
C
aC0
166
SU084
PODP3v166
1.0
1
5
4
4
oxA3
125/50,
150/60
SL24V
PODPMT60X150
1.0
1
5
4
4
oxA3
166/66
SL24W
PODPMT66X166
1.0
1
5
4
3
oxB1
180/60
SL2FE
PODPMT60X180
2.0
1
5
4
3
oxB1
200/66
SL2FF
PODPMT66X200
2.0
The following list explains all the entries in the Comments columns of these Tables 3.22–3.24.
*These chips have no specification number.
ES = Engineering Sample. These chips were not sold through normal channels but were designed for development
and testing purposes.
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HS = Heat Spreader Package. This indicates a chip with a metal plate on the top, which is used to spread heat
away from the center part of the chip. The heat spreader helps the chip run cooler; however, most later chips use
a smaller, more powerful and efficient die, and Intel has been able to eliminate the heat spreader from these.
DP = Dual Processor version where Type 0 is primary only, Type 2 is secondary only, and Type 0 or 2 is either.
MD = Minimum Delay timing restrictions on several processor signals.
STD = Standard voltage range. The range for the C2 and subsequent steppings of the Pentium processor is
3.135v to 3.6v. The voltage range for B-step parts remains at 3.135v–3.465v. Note that all E0-step production
parts are standard voltage.
VR = Voltage Reduced (3.300v–3.465v).
VRE = VR and Extended (3.45v–3.60v).
VRT = Voltage Reduction Technology.
TCP = Tape Carrier Package.
BOX = A retail boxed processor with a standard passive heat sink.
BOXF = A retail boxed processor with an active (fan-cooled) heat sink.
The absence of a package type in the comments column means the processor is SPGA by default.
2.285v = This is a mobile Pentium processor with MMX technology with a core operating voltage of
2.285v–2.665v.
MAXF = The part may run only at the maximum specified frequency. Specifically, a 200MHz may be run at
200MHz +0/-5 MHz (195–200MHz), and a 166MHz may be run at 166MHz +0/-5MHz (161–166MHz).
BOXUF = This part also ships as a boxed processor with an unattached fan heat sink.
1.8v = This is a mobile Pentium processor with MMX technology with a core operating voltage of
1.665v–1.935v and an I/O operating voltage of 2.375v–2.625v.
2.2v = This Pentium processor with MMX technology with a core operating voltage of 2.10v–2.34v.
2.0v = This is a mobile Pentium processor with MMX technology with a core operating voltage of
1.850v–2.150v and an I/O operating voltage of 2.375v–2.625v.
STP = The cB1 stepping is logically equivalent to the C2-step, but on a different manufacturing process. The
mcB1 step is logically equivalent to the cB1 step (except it does not support DP, APIC, or FRC). The mcB1, mA1,
mA4, and mcC0-steps also use Intel’s VRT (Voltage Reduction Technology), and are available in the TCP and
SPGA package, primarily to support mobile applications. The mxA3 is logically equivalent to the xA3 stepping,
except it does not support DP or APIC.
NO = Part meets the specifications but is not tested to support 82498/82493 and 82497/82492 cache timings.
In these tables, the processor Type heading refers to the dual processor capabilities of the
Pentium. Versions indicated with a Type 0 can be used only as a primary processor, while those
marked as Type 2 can be used only as the secondary processor in a pair. If the processor is marked
as Type 0/2, it can serve as the primary or secondary processor, or both.
The Family designation for all Pentiums is 5 (for 586), while the model indicates the particular
revision. Model 1 indicates the first-generation 60/66MHz version, whereas Model 2 or later indicates the second-generation 75+MHz version. The stepping number is the actual revision of the
particular model. The family, model, and stepping number can be read by software such as the
Intel CPUID program. These also correspond to a particular manufacturer stepping code, which is
how Intel designates the chips in-house. These are usually an alphanumeric code. For example,
stepping 5 of the Model 2 Pentium is also known as the C2 stepping inside Intel.
Manufacturing stepping codes that begin with an m indicate a mobile processor. Most Pentium
processors come in a standard Ceramic Pin Grid Array (CPGA) package; however, the mobile
processors also use the tape carrier package (TCP). Now there is also a Plastic Pin Grid Array
(PPGA) package being used to reduce cost.
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To determine the specifications of a given processor, you need to look up the S-spec number in
the table of processor specifications. To find your S-spec number, you have to read it off of the
chip directly. It can be found printed on both the top and bottom of the chip. If your heat sink is
glued on, remove the chip and heat sink from the socket as a unit and read the numbers from
the bottom of the chip. Then you can look up the S-spec number in the table; it will tell you the
specifications of that particular processor. Intel is introducing new chips all the time, so visit their
Web site and search for the Pentium processor “Quick Reference Guide” in the developer portion
of their site. There you will find a complete listing of all current processor specifications by S-spec
number.
One interesting item to note is that there are several subtly different voltages required by different Pentium processors. Table 3.27 summarizes the different processors and their required voltages:
Table 3.27
Pentium Processor Voltages
Model
Stepping
Voltage Spec.
Voltage Range
1
—
Std.
4.75–5.25v
1
—
5v1
4.90–5.25v
1
—
5v2
4.90–5.40v
1
—
5v3
5.15–5.40v
2+
B1-B5
Std.
3.135–3.465v
2+
C2+
Std.
3.135–3.600v
2+
—
VR
3.300–3.465v
2+
B1-B5
VRE
3.45–3.60v
2+
C2+
VRE
3.40–3.60v
4+
—
MMX
2.70–2.90v
4
3
Mobile
2.285–2.665v
4
3
Mobile
2.10–2.34v
8
1
Mobile
1.850–2.150v
8
1
Mobile
1.665–1.935v
Many of the newer Pentium motherboards have jumpers that allow for adjustments to the different voltage ranges. If you are having problems with a particular processor, it may not be matched
correctly to your motherboard voltage output.
If you are purchasing an older, used Pentium system today, I recommend using only Model 2
(second generation) or later version processors that are available in 75MHz or faster speeds. I
would definitely want stepping C2 or later. Virtually all the important bugs and problems were
fixed in the C2 and later releases. The newer Pentium processors have no serious bugs to worry
about.
AMD-K5
The AMD-K5 is a Pentium-compatible processor developed by AMD and available as the PR75,
PR90, PR100, PR120, PR133, and PR-166. Because it is designed to be physically and functionally
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compatible, any motherboard that properly supports the Intel Pentium should support the AMDK5. However, a BIOS upgrade might be required to properly recognize the AMD-K5. AMD keeps a
list of motherboards that have been tested for compatibility.
The K5 has the following features:
■ 16KB instruction cache, 8KB write-back data cache
■ Dynamic execution—branch prediction with speculative execution
■ Five-stage RISC-like pipeline with six parallel functional units
■ High-performance floating-point unit (FPU)
■ Pin-selectable clock multiples of 1.5x and 2x
The K5 is sold under the P-Rating system, which means that the number on the chip does not
indicate true clock speed, only apparent speed when running certain applications.
√√ See “AMD P-Ratings,” p. 49.
Note that several of these processors do not run at their apparent rated speed. For example, the
PR-166 version actually runs at only 117 true MHz. Sometimes this can confuse the system BIOS,
which may report the true speed rather than the P-Rating, which compares the chip against an
Intel Pentium of that speed. AMD claims that because of architecture enhancements over the
Pentium, they do not need to run the same clock frequency to achieve that same performance.
Even with such improvements, AMD markets the K5 as a fifth-generation processor, just like the
Pentium.
The AMD-K5 operates at 3.52 volts (VRE Setting). Some older motherboards default to 3.3 volts,
which is below specification for the K5 and could cause erratic operation.
Pseudo Fifth-Generation Processors
There is at least one processor that, while generally regarded as a fifth-generation processor, lacks
many of the functions of that class of chip—the IDT Centaur C6 Winchip. True fifth-generation
chips would have multiple internal pipelines, which is called superscalar architecture, allowing
more than one instruction to be processed at one time. They would also feature branch prediction, another fifth-generation chip feature. As it lacks these features, the C6 is more closely
related to a 486; however, the performance levels and the pinout put it firmly in the class with
Pentium processors. It has turned out to be an ideal Pentium Socket 7-compatible processor for
low-end systems.
IDT Centaur C6 Winchip
The C6 processor is a recent offering from Centaur, a wholly owned subsidiary of IDT (Integrated
Device Technologies). It is Socket 7-compatible with Intel’s Pentium, includes MMX extensions,
and is available at clock speeds of 180, 200, 225, and 240MHz. Pricing is below Intel on the
Pentium MMX.
Centaur is led by Glenn Henry, who spent more than two decades as a computer architect at
IBM and six years as chief technology officer at Dell Computer Corp. The company is a wellestablished semiconductor manufacturer well-known for SRAM and other components.
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As a manufacturer, IDT owns its own fabs (semiconductor manufacturing plants), which will help
keep costs low on the C6 Winchip. Their expertise in SRAM manufacturing may be applied in
new versions of the C6, which integrate onboard L2 cache in the same package as the core
processor, similar to the Pentium Pro.
The C6 has 32KB each of instruction and data cache, just like AMD’s K6 and Cyrix’s 6x86MX, yet
it has only 5.4 million transistors, compared with the AMD chip’s 8.8 million and the Cyrix
chip’s 6.5 million. This allows for a very small processor die, which also reduces power consumption. Centaur achieved this small size with a streamlined design. Unlike competitor chips, the C6
is not superscalar—it issues only one instruction per clock cycle like the 486. However, with large
caches, an efficient memory-management unit, and careful performance optimization of commonly used instructions, the C6 achieves performance that’s comparable to a Pentium. Another
benefit of the C6’s simple design is low power consumption—low enough for notebook PCs.
Neither AMD nor Cyrix has a processor with power consumption low enough for most laptop
designs.
To keep the design simple, Centaur compromised on floating-point and MMX speed and focused
instead on typical application performance. As a result, the chip’s performance trails the other
competitors’ on some multimedia applications and games.
Intel P6 (686) Sixth-Generation Processors
The P6 (686) processors represent a new generation with features not found in the previous generation units. The P6 processor family began when the Pentium Pro was released in November
1995. Since then, many other P6 chips have been released by Intel, all using the same basic P6
core processor as the Pentium Pro. Table 3.28 shows the variations in the P6 family of processors.
Table 3.28
Intel P6 Processor Variations
Pentium Pro
Original P6 processor, includes 256KB, 512KB, or 1MB of full core-speed L2 cache
Pentium II
P6 with 512KB of half core speed L2 cache
Pentium II Xeon
P6 with 512KB, 1MB, or 2MB of full-core speed L2 cache
Celeron
P6 with no L2 cache
Celeron-A
P6 with 128KB of on-die full-core speed L2 cache
Pentium III
P6 with SSE (MMX2), 512KB of half-core speed L2 cache
Pentium IIPE
P6 with 256KB of full-core speed L2 cache
Pentium III Xeon
P6 with SSE (MMX2), 512KB, 1MB, or 2MB of full-core speed L2 cache
Even more are expected in this family, including versions of the Pentium III with on-die full-core
speed L2 cache, and faster versions of the Celeron.
The main new feature in the fifth-generation Pentium processors was the superscalar architecture,
where two instruction execution units could execute instructions simultaneously in parallel. Later
fifth-generation chips also added MMX technology to the mix, as well. So then what did Intel add
in the sixth-generation to justify calling it a whole new generation of chip? Besides many minor
improvements, the real key features of all sixth-generation processors are Dynamic Execution and
the Dual Independent Bus (DIB) architecture, plus a greatly improved superscalar design.
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Dynamic Execution enables the processor to execute more instructions on parallel, so that tasks
are completed more quickly. This technology innovation is comprised of three main elements:
■ Multiple branch prediction, to predict the flow of the program through several branches
■ Dataflow analysis, which schedules instructions to be executed when ready, independent of
their order in the original program
■ Speculative execution, which increases the rate of execution by looking ahead of the program
counter and executing instructions that are likely to be needed
Branch prediction is a feature formerly found only in high-end mainframe processors. It allows
the processor to keep the instruction pipeline full while running at a high rate of speed. A special
fetch/decode unit in the processor uses a highly optimized branch prediction algorithm to predict
the direction and outcome of the instructions being executed through multiple levels of
branches, calls, and returns. It is like a chess player working out multiple strategies in advance of
game play by predicting the opponent’s strategy several moves into the future. By predicting the
instruction outcome in advance, the instructions can be executed with no waiting.
Dataflow analysis studies the flow of data through the processor to detect any opportunities for
out-of-order instruction execution. A special dispatch/execute unit in the processor monitors
many instructions and can execute these instructions in an order that optimizes the use of the
multiple superscalar execution units. The resulting out-of-order execution of instructions can
keep the execution units busy even when cache misses and other data-dependent instructions
might otherwise hold things up.
Speculative execution is the processor’s capability to execute instructions in advance of the actual
program counter. The processor’s dispatch/execute unit uses dataflow analysis to execute all available instructions in the instruction pool and store the results in temporary registers. A retirement
unit then searches the instruction pool for completed instructions that are no longer data dependent on other instructions to run, or which have unresolved branch predictions. If any such
completed instructions are found, the results are committed to memory by the retirement unit or
the appropriate standard Intel architecture in the order they were originally issued. They are then
retired from the pool.
Dynamic Execution essentially removes the constraint and dependency on linear instruction
sequencing. By promoting out-of-order instruction execution, it can keep the instruction units
working rather than waiting for data from memory. Even though instructions can be predicted
and executed out of order, the results are committed in the original order so as not to disrupt or
change program flow. This allows the P6 to run existing Intel architecture software exactly as the
P5 (Pentium) and previous processors did, just a whole lot more quickly!
The other main P6 architecture feature is known as the Dual Independent Bus. This refers to the
fact that the processor has two data buses, one for the system (motherboard) and the other just
for cache. This allows the cache memory to run at speeds previously not possible.
Previous P5 generation processors have only a single motherboard host processor bus, and all
data, including cache transfers, must flow through it. The main problem with that is the cache
memory was restricted to running at motherboard bus speed, which was 66MHz until recently
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and has now moved to 100MHz. We have cache memory today that can run 500MHz or more,
and main memory (SDRAM) that runs at 66 and 100MHz, so a method was needed to get faster
memory closer to the processor. The solution was to essentially build in what is called a backside
bus to the processor, otherwise known as a dedicated cache bus. The L2 cache would then be
connected to this bus and could run at any speed. The first implementation of this was in the
Pentium Pro, where the L2 cache was built right into the processor package and ran at the full
core processor speed. Later, that proved to be too costly, so the L2 cache was moved outside of
the processor package and onto a cartridge module, which we now know as the Pentium II/III.
With that design, the cache bus could run at any speed, with the first units running the cache at
half-processor speed.
By having the cache on a backside bus directly connected to the processor, the speed of the cache
is scalable to the processor. In current PC architecture—66MHz Pentiums all the way through the
333MHz Pentium IIs—the motherboard runs at a speed of 66MHz. Newer Pentium II systems run
a 100MHz motherboard bus and have clock speeds of 350MHz and higher. If the cache were
restricted to the motherboard as is the case with Socket 7 (P5 processor) designs, the cache memory would have to remain at 66MHz, even though the processor was running as fast as 333MHz.
With newer boards, the cache would be stuck at 100MHz, while the processor ran as fast as
500MHz or more. With the Dual Independent Bus (DIB) design in the P6 processors, as the
processor runs faster, at higher multiples of the motherboard speed, the cache would increase by
the same amount that the processor speed increases. The cache on the DIB is coupled to processor speed, so that doubling the speed of the processor also doubles the speed of the cache.
The DIB architecture is necessary to have decent processor performance in the 300MHz and
beyond range. Older Socket 7 (P5 processor) designs will not be capable of moving up to these
higher speeds without suffering a tremendous performance penalty due to the slow motherboardbound L2 cache. That is why Intel is not developing any Pentium (P5 class) processors beyond
266MHz; however, the P6 processors will be available in speeds of up to 500MHz or more.
Finally, the P6 architecture upgrades the superscalar architecture of the P5 processors by adding
more instruction execution units, and by breaking down the instructions into special micro-ops.
This is where the CISC (Complex Instruction Set Computer) instructions are broken down into
more RISC (Reduced Instruction Set Computer) commands. The RISC-level commands are smaller
and easier for the parallel instruction units to execute more efficiently. With this design, Intel has
brought the benefits of a RISC processor—high-speed dedicated instruction execution—to the
CISC world. Note that the P5 had only two instruction units, while the P6 has at least six separate dedicated instruction units. It is said to be three-way superscalar, because the multiple
instruction units can execute up to three instructions in one cycle.
Other improvements in efficiency also are included in the P6 architecture: built-in multiprocessor
support, enhanced error detection and correction circuitry, and optimization for 32-bit software.
Rather than just being a faster Pentium, the Pentium Pro, Pentium II/III, and other
sixth-generation processors have many feature and architectural improvements. The core of the
chip is very RISC-like, while the external instruction interface is classic Intel CISC. By breaking
down the CISC instructions into several different RISC instructions and running them down parallel execution pipelines, the overall performance is increased.
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Compared to a Pentium at the same clock speed, the P6 processors are faster—as long as you’re
running 32-bit software. The P6 Dynamic Execution is optimized for performance primarily when
running 32-bit software such as Windows NT. If you are using 16-bit software, such as Windows
95 or 98 (which operate part time in a 16-bit environment) and most older applications, the P6
will not provide as marked a performance improvement over similarly speed-rated Pentium and
Pentium-MMX processors. That’s because the Dynamic Execution capability will not be fully
exploited. Because of this, Windows NT is often regarded as the most desirable operating system
for use with Pentium Pro/II/III/Celeron processors. While this is not exactly true (a Pentium
Pro/II/III/Celeron will run fine under Windows 95/98), Windows NT does take better advantage
of the P6’s capabilities. Note that it is really not so much the operating system but which applications you use. Software developers can take steps to gain the full advantages of the
sixth-generation processors. This includes using modern compilers that can improve performance
for all current Intel processors, writing 32-bit code where possible, and making code as predictable as possible to take advantage of the processor’s Dynamic Execution multiple branch prediction capabilities.
Pentium Pro Processors
Intel’s successor to the Pentium is called the Pentium Pro. The Pentium Pro was the first chip in
the P6 or sixth-generation processor family. It was introduced in November 1995, and became
widely available in 1996. The chip is a 387-pin unit that resides in Socket 8, so it is not
pin-compatible with earlier Pentiums. The new chip is unique among processors as it is constructed in a Multi-Chip Module (MCM) physical format, which Intel is calling a Dual Cavity
PGA (Pin Grid Array) package. Inside the 387-pin chip carrier are two dies. One contains the
actual Pentium Pro processor (shown in Figure 3.36), and the other a 256KB (the Pentium Pro
with 256KB cache is shown in Figure 3.37), 512KB, or 1MB (the Pentium Pro with 1MB cache is
shown in Figure 3.37) L2 cache. The processor die contains 5.5 million transistors, the 256KB
cache die contains 15.5 million transistors, and the 512KB cache die(s) have 31 million transistors each, for a potential total of nearly 68 million transistors in a Pentium Pro with 1MB of
internal cache! A Pentium Pro with 1MB cache has two 512KB cache die and a standard P6
processor die (see Figure 3.38).
The main processor die includes a 16KB split L1 cache with an 8KB two-way set associative cache
for primary instructions, and an 8KB four-way set associative cache for data.
Another sixth-generation processor feature found in the Pentium Pro is the Dual Independent
Bus (DIB) architecture, which addresses the memory bandwidth limitations of
previous-generation processor architectures. Two buses make up the DIB architecture: the L2
cache bus (contained entirely within the processor package) and the processor-to-main memory
system bus. The speed of the dedicated L2 cache bus on the Pentium Pro is equal to the full core
speed of the processor. This was accomplished by embedding the cache chips directly into the
Pentium Pro package. The DIB processor bus architecture addresses processor-to-memory bus
bandwidth limitations. It offers up to three times the performance bandwidth of the single-bus,
“Socket 7” generation processors, such as the Pentium.
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Figure 3.36
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155
Pentium Pro processor die. Photograph used by permission of Intel Corporation.
Figure 3.37 Pentium Pro processor with 256KB L2 cache (the cache is on the left side of the processor die). Photograph used by permission of Intel Corporation.
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Figure 3.38 Pentium Pro processor with 1MB L2 cache (the cache is in the center and right portions
of the die). Photograph used by permission of Intel Corporation.
Table 3.29 shows Pentium Pro processor specifications. Table 3.30 shows the specifications for
each model within the Pentium Pro family, as there are many variations from model to model.
Table 3.29
Pentium Pro Family Processor Specifications
Introduced
November 1995
Maximum rated speeds
150, 166, 180, 200MHz
CPU
2.5x, 3x
Internal registers
32-bit
External data bus
64-bit
Memory address bus
36-bit
Addressable memory
64GB
Virtual memory
64TB
Integral L1-cache size
8KB code, 8KB data (16KB total)
Integrated L2-cache bus
64-bit, full core-speed
Socket/Slot
Socket 8
Physical package
387-pin Dual Cavity PGA
Package dimensions
2.46 (6.25cm) × 2.66 (6.76cm)
Math coprocessor
Built-in FPU
Power management
SMM (system management mode)
Operating voltage
3.1v or 3.3v
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Table 3.30
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157
Pentium Pro Processor Specifications by Processor Model
Pentium Pro Processor (200MHz) with 1MB Integrated Level 2 Cache
Introduction date
August 18, 1997
Clock speeds
200MHz (66MHz × 3)
Number of transistors
5.5 million (0.35 micron process), plus 62 million in 1MB L2 cache
(0.35 micron)
Cache Memory
8Kx2 (16KB) L1, 1MB core-speed L2
Die Size
0.552 (14.0mm)
Pentium Pro Processor (200MHz)
Introduction date
November 1, 1995
Clock speeds
200MHz (66MHz × 3)
iCOMP Index 2.0 rating
220
Number of transistors
5.5 million (0.35 micron process), plus 15.5 million in 256KB L2 cache
(0.6 micron), or 31 million in 512KB L2 cache (0.35 micron)
Cache Memory
8Kx2 (16KB) L1, 256KB or 512KB core-speed L2
Die Size
0.552 inches per side (14.0mm)
Pentium Pro Processor (180MHz)
Introduction date
November 1, 1995
Clock speeds
180MHz (60MHz × 3)
iCOMP Index 2.0 rating
197
Number of transistors
5.5 million (0.35 micron process), plus 15.5 million in 256KB L2 cache
(0.6 micron)
Cache Memory
8Kx2 (16KB) L1, 256KB core-speed L2
Die Size
0.552 inches per side (14.0mm)
Pentium Pro Processor (166MHz)
Introduction date
November 1, 1995
Clock speeds
166MHz (66MHz × 2.5)
Number of transistors
5.5 million (0.35 micron process), plus 31 million in 512KB L2 cache
(0.35 micron)
Cache Memory
8Kx2 L1, 512KB core-speed L2
Die Size
0.552 inches per side (14.0mm)
Pentium Pro Processor (150MHz)
Introduction date
November 1, 1995
Clock speeds
150MHz (60MHz × 2.5)
Number of transistors
5.5 million (0.6 micron process), plus 15.5 million in 256KB L2 cache
(0.6 micron)
Cache Memory
8Kx2 speed L2
Die Size
0.691 inches per side (17.6mm)
As you saw in Table 3.3, performance comparisons on the iCOMP 2.0 Index rate a classic Pentium
200MHz at 142, whereas a Pentium Pro 200MHz scores an impressive 220. Just for comparison,
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note that a Pentium MMX 200MHz falls right about in the middle in regards to performance at
182. Keep in mind that using a Pentium Pro with any 16-bit software applications will nullify
much of the performance gain shown by the iCOMP 2.0 rating.
Like the Pentium before it, the Pentium Pro runs clock multiplied on a 66MHz motherboard. The
following table lists speeds for Pentium Pro processors and motherboards.
CPU Type/Speed
CPU Clock
Motherboard Speed
Pentium Pro 150
2.5x
60
Pentium Pro 166
2.5x
66
Pentium Pro 180
3x
60
Pentium Pro 200
3x
66
The integrated L2 cache is one of the really outstanding features of the Pentium Pro. By building
the L2 cache into the CPU and getting it off the motherboard, they can now run the cache at full
processor speed rather than the slower 60 or 66MHz motherboard bus speeds. In fact, the L2
cache features its own internal 64-bit backside bus, which does not share time with the external
64-bit frontside bus used by the CPU. The internal registers and data paths are still 32-bit, as with
the Pentium. By building the L2 cache into the system, motherboards can be cheaper because
they no longer require separate cache memory. Some boards may still try to include cache memory in their design, but the general consensus is that L3 cache (as it would be called) would offer
less improvement with the Pentium Pro than with the Pentium.
One of the features of the built-in L2 cache is that multiprocessing is greatly improved. Rather
than just SMP, as with the Pentium, the Pentium Pro supports a new type of multiprocessor configuration called the Multiprocessor Specification (MPS 1.1). The Pentium Pro with MPS allows
configurations of up to four processors running together. Unlike other multiprocessor configurations, the Pentium Pro avoids cache coherency problems because each chip maintains a separate
L1 and L2 cache internally.
Pentium Pro-based motherboards are pretty much exclusively PCI and ISA bus-based, and Intel is
producing their own chipsets for these motherboards. The first chipset was the 450KX/GX (codenamed Orion), while the most recent chipset for use with the Pentium Pro is the 440LX
(Natoma). Due to the greater cooling and space requirements, Intel designed the new ATX motherboard form factor to better support the Pentium Pro and other future processors, such as the
Pentium II. Even so, the Pentium Pro can be found in all types of motherboard designs; ATX is
not mandatory.
◊◊ See “Motherboard Form Factors,” p. 204, and “Sixth-Generation (P6 Pentium Pro/Pentium II Class) Chipsets,”
p. 252.
Some Pentium Pro system manufacturers have been tempted to stick with the Baby-AT form factor. The big problem with the standard Baby-AT form factor is keeping the CPU properly cooled.
The massive Pentium Pro processor consumes more than 25 watts and generates an appreciable
amount of heat.
Four special Voltage Identification (VID) pins are on the Pentium Pro processor. These pins can be
used to support automatic selection of power supply voltage. This means that a Pentium Pro
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motherboard does not have voltage regulator jumper settings like most Pentium boards, which
greatly eases the setup and integration of a Pentium Pro system. These pins are not actually signals, but are either an open circuit in the package or a short circuit to voltage. The sequence of
opens and shorts define the voltage required by the processor. In addition to allowing for automatic voltage settings, this feature has been designed to support voltage specification variations
on future Pentium Pro processors. The VID pins are named VID0 through VID3 and the definition of these pins is shown in Table 3.31. A 1 in this table refers to an open pin and 0 refers to a
short to ground. The voltage regulators on the motherboard should supply the voltage that is
requested or disable itself.
Table 3.31
Pentium Pro Voltage Identification Definition
VID[3:0]
Voltage
Setting
VID[3:0] Voltage Setting
0000
3.5
1000
2.7
0001
3.4
1001
2.6
0010
3.3
1010
2.5
0011
3.2
1011
2.4
0100
3.1
1100
2.3
0101
3.0
1101
2.2
0110
2.9
1110
2.1
0111
2.8
1111
No CPU present
Most Pentium Pro processors run at 3.3v, but a few run at 3.1v. Although those are the only versions available now, support for a wider range of VID settings will benefit the system in meeting
the power requirements of future Pentium Pro processors. Note that the 1111 (or all opens) ID
can be used to detect the absence of a processor in a given socket.
The Pentium Pro never did become very popular on the desktop, but has found a niche in file
server applications due primarily to the full core-speed high-capacity internal L2 cache. It is
expected that Intel will introduce only one or two more variations of the Pentium Pro, primarily
as upgrade processors for those who want to install a faster CPU in their existing Pentium Pro
motherboard. In most cases, it would be wiser to install a new Pentium II motherboard instead.
The following tables list the unique specifications of the different models of the Pentium Pro.
As with other processors, the Pentium Pro has been available in a number of different revisions
and steppings. The following table shows all the versions of the Pentium Pro. They can be identified by the Specification number printed on the top and bottom of the chip.
Type
Family
Model
Stepping
Mfg.
Stepping
L2 Size/
Stepping
Speed
Core/Bus
Spec.
(+/-5%)
Voltage
Notes
0
0
0
0
6
6
6
6
1
1
1
1
1
1
1
1
B0
B0
B0
B0
256/a
256/a
256/a
256/a
133/66
150/60
133/66
150/60
Q0812
Q0813
Q0815
Q0816
3.1v
3.1v
3.1v
3.1v
3,4
3,4
3,4
3,4
(continues)
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(continued)
Type
Family
Model
Stepping
Mfg.
Stepping
L2 Size/
Stepping
Speed
Core/Bus
Spec.
(+/-5%)
Voltage
Notes
0
0
0
0
0
0
0
0
0
0
0
0
6
6
6
6
6
6
6
6
6
6
6
6
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
6
6
6
6
6
B0
B0
B0
C0
C0
C0
C0
sA0
sA0
sA0
sA0
sA0
150/60
150/60
150/60
150/60
150/60
150/60
150/60
180/60
200/66
180/60
200/66
166/66
SY002
SY011
SY014
Q0822
Q0825
Q0826
SY010
Q0858
Q0859
Q0860
Q0861
Q0864
3.1v
3.1v
3.1v
3.1v
3.1v
3.1v
3.1v
3.3v
3.3v
3.3v
3.3v
3.3v
3
4
4
4,5
4,5
4
0
6
1
6
sA0 2
200/66
Q0865
3.3v
4
0
0
0
0
0
0
0
0
0
0
0
0
6
6
6
6
6
6
6
6
6
6
6
6
1
1
1
1
1
1
1
1
1
1
1
1
6
6
6
6
6
7
7
7
7
7
7
7
sA0
sA0
sA0
sA0
sA0
sA1
sA1
sA1
sA1
sA1
sA1
sA1
180/60
200/66
180/60
180/60
200/66
200/66
180/60
200/66
180/60
200/66
200/66
166/66
Q0873
Q0874
Q0910
SY012
SY013
Q076
Q0871
Q0872
Q0907
Q0908
Q0909
Q0918
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
4
4
0
6
1
7
sA1
200/66
Q0920
3.3v
4
0
6
1
7
sA1
200/66
Q0924
3.3v
4
0
0
0
0
0
0
0
0
0
0
6
6
6
6
6
6
6
6
6
6
1
1
1
1
1
1
1
1
1
1
7
7
7
7
7
7
7
7
7
7
sA1
sA1
sA1
sA1
sA1
sA1
sA1
sA1
sA1
sA1
256/a
256/a
256/a
256/a
256/a
256/a
256/a
256/a
256/a
256/a
256/a
512/
Pre 6
512/
Pre 6
256/a
256/a
256/a
256/a
256/a
256/a
256/a
256/a
256/a
256/a
256/b
512/
Pre 6
512/
Pre 6
512/
Pre 6
512/a
512/a
512/b
512/b
256/a
256/a
256/b
256/b
256/b
256/b
166/66
200/66
166/66
200/66
200/66
200/66
180/60
200/66
180/60
200/66
Q0929
Q932
Q935
Q936
SL245
SL247
SU103
SU104
SY031
SY032
3.3v
3.3v
3.3v
3.3v
3.5v
3.5v
3.3v
3.3v
3.3v
3.3v
4
4
4
4
7
7
8
8
2
2
2
2
2
2
2
2
2
2
3,4
4
4
7
4
4
4
4
4
4
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Type
Family
Model
Stepping
Mfg.
Stepping
L2 Size/
Stepping
Speed
Core/Bus
Spec.
(+/-5%)
Voltage
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
7
7
7
7
7
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
sA1
sA1
sA1
sA1
sA1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
sB1
512/a
256/a
256/b
512/b
512/b
512/b
512/b
512/b
512/b
256/b
256/b
256/b
256/b
256/b
256/b
256/b
256/b
256/b
256/b
512/b
512/b
256/b
256/b
256/b
256/b
512/b
1024/g
1024/g
166/66
180/60
200/66
166/66
200/66
166/66
166/66
200/66
200/66
180/60
200/66
180/60
200/66
200/66
200/66
180/60
200/66
180/60
200/66
166/66
200/66
180/60
200/66
200/66
200/66
166/66
200/66
200/66
SY034
SY039
SY040
SY047
SY048
Q008
Q009
Q010
Q011
Q033
Q034
Q035
Q036
Q083
Q084
SL22S
SL22T
SL22U
SL22V
SL22X
SL22Z
SL23L
SL23M
SL254
SL255
SL2FJ
SL259
SL25A
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.5v
3.5v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.3v
3.5v
3.5v
3.3v
3.3v
3.3v
Notes
4
4
4
4
4
4
4
4
7
7
9
8
8
7
7
8
1. L2 cache stepping refers to the silicon revision of the 256KB, 512KB, or 1MB on-chip L2 cache. The “a” designation
refers to the first production steppings; the “b” to the second production steppings, and so on.
2. The sA0 stepping is logically equivalent to the C0 stepping, but on a different manufacturing process.
3. The VID pins are not supported on these parts.
4. These are engineering samples only, provided under a Pentium Pro processor nondisclosure loan agreement.
5. The VID pins are functional but not tested on these parts.
6. These sample parts are equipped with a preproduction 512KB L2 cache.
7. These components have additional specification changes associated with them:
a. Primary Voltage = 3.5v
b. Max Thermal Design Power = 39.4W @ 200MHz, 256KB L2
c. Max Current = 11.9A
d. The VID pins are not supported on these parts.
8. This is a boxed Pentium Pro processor with an unattached fan heat sink.
9. This part also ships as a boxed processor with an unattached fan heat sink.
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Pentium II Processors
Intel revealed the Pentium II in May 1997. Prior to its official unveiling, the Pentium II processor
was popularly referred to by its code name Klamath, and was surrounded by much speculation
throughout the industry. The Pentium II is essentially the same sixth-generation processor as the
Pentium Pro, with MMX technology added (which included double the L1 cache and 57 new
MMX instructions); however, there are a few twists to the design. The Pentium II processor die is
shown in Figure 3.39.
Figure 3.39
Pentium II Processor die. Photograph used by permission of Intel Corporation.
From a physical standpoint, it is truly something new. Abandoning the chip in a socket approach
used by virtually all processors up until this point, the Pentium II chip is characterized by its
Single Edge Contact (SEC) cartridge design. The processor, along with several L2 cache chips, is
mounted on a small circuit board (much like an oversized-memory SIMM) as shown in Figure
3.40, which is then sealed in a metal and plastic cartridge. The cartridge is then plugged into the
motherboard through an edge connector called Slot 1, which looks very much like an adapter
card slot.
There are two variations on these cartridges, called SECC (Single Edge Contact Cartridge) and
SECC2. Figure 3.41 shows a diagram of the SECC package. Figure 3.42 shows the SECC2 package.
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Figure 3.40
Corporation.
Chapter 3
Pentium II Processor Board (inside SEC cartridge). Photograph used by permission of Intel
Thermal Plate
Clips
Processor Substrate
with L1 and L2 cache
Cover
Figure 3.41
163
SECC components showing enclosed processor board.
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Processor Substrate
with L1 and L2 cache
Cover
Figure 3.42
board.
2 Single Edge Contact Cartridge, rev. 2 components showing half-enclosed processor
As you can see from these figures, the SECC2 version is cheaper to make because it uses fewer
overall parts. It also allows for a more direct heat sink attachment to the processor for better cooling. Intel transitioned from SECC to SECC2 in the beginning of 1999; all newer PII/PIII cartridge
processors use the improved SECC2 design.
By using separate chips mounted on a circuit board, Intel can build the Pentium II much less
expensively than the multiple die within a package used in the Pentium Pro. They can also use
cache chips from other manufacturers, and more easily vary the amount of cache in future
processors compared to the Pentium Pro design.
At present, Intel is offering Pentium II processors with the following speeds:
CPU Type/Speed
CPU Clock
Motherboard Speed
Pentium II 233MHz
3.5x
66MHz
Pentium II 266MHz
4x
66MHz
Pentium II 300MHz
4.5x
66MHz
Pentium II 333MHz
5x
66MHz
Pentium II 350MHz
3.5x
100MHz
Pentium II 400MHz
4x
100MHz
Pentium II 450MHz
4.5x
100MHz
The Pentium II processor core has 7.5 million transistors and is based on Intel’s advanced P6
architecture. The Pentium II started out using .35 micron process technology, although the
333MHz and faster Pentium IIs are based on 0.25 micron technology. This enables a smaller die,
allowing increased core frequencies and reduced power consumption. At 333MHz, the Pentium II
processor delivers a 75–150 percent performance boost, compared to the 233MHz Pentium
processor with MMX technology, and approximately 50 percent more performance on multimedia benchmarks. These are very fast processors, at least for now. As shown in Table 3.3, the
iCOMP 2.0 Index rating for the Pentium II 266MHz chip is more than twice as fast as a classic
Pentium 200MHz.
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Aside from speed, the best way to think of the Pentium II is as a Pentium Pro with MMX technology instructions and a slightly modified cache design. It has the same multiprocessor scalability
as the Pentium Pro, as well as the integrated L2 cache. The 57 new multimedia-related instructions carried over from the MMX processors and the capability to process repetitive loop commands more efficiently are also included. Also included as a part of the MMX upgrade is double
the internal L1 cache from the Pentium Pro (from 16KB total to 32KB total in the Pentium II).
The original Pentium II processors were manufactured using a 0.35 micron process. More recent
models, starting with the 333MHz version, have been manufactured using a newer 0.25 micron
process. Intel is considering going to a 0.18 micron process in the future. By going to the smaller
process, power draw is greatly reduced.
Maximum power usage for the Pentium II is shown in the following table.
Core Speed
Power Draw
Process
Voltage
450MHz
27.1w
0.25 micron
2.0v
400MHz
24.3w
0.25 micron
2.0v
350MHz
21.5w
0.25 micron
2.0v
333MHz
23.7w
0.25 micron
2.0v
300MHz
43.0w
0.35 micron
2.8v
266MHz
38.2w
0.35 micron
2.8v
233MHz
34.8w
0.35 micron
2.8v
You can see that the highest speed 450MHz version of the Pentium II actually uses less power
than the slowest original 233MHz version! This was accomplished by using the smaller 0.25
micron process and running the processor on a lower voltage of only 2.0v. Future Pentium III
processors will use the 0.25- and 0.18 micron processes and even lower voltages to continue this
trend.
The Pentium II includes Dynamic Execution, which describes unique performance-enhancing
developments by Intel and was first introduced in the Pentium Pro processor. Major features of
Dynamic Execution include Multiple Branch Prediction, which speeds execution by predicting
the flow of the program through several branches; Dataflow Analysis, which analyzes and modifies the program order to execute instructions when ready; and Speculative Execution, which
looks ahead of the program counter and executes instruction that are likely to be needed. The
Pentium II processor expands on these capabilities in sophisticated and powerful new ways to
deliver even greater performance gains.
Like the Pentium Pro, the Pentium II also includes DIB architecture. The term Dual Independent
Bus comes from the existence of two independent buses on the Pentium II processor—the L2
cache bus and the processor-to-main-memory system bus. The Pentium II processor can use both
buses simultaneously, thus getting as much as 2× more data in and out of the Pentium II processor than a single-bus architecture processor. The DIB architecture enables the L2 cache of the
333MHz Pentium II processor to run 2 1/2 times as fast as the L2 cache of Pentium processors. As
the frequency of future Pentium II processors increases, so will the speed of the L2 cache. Also,
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the pipelined system bus enables simultaneous parallel transactions instead of singular sequential
transactions. Together, these DIB architecture improvements offer up to three times the bandwidth performance over a single-bus architecture as with the regular Pentium.
Table 3.32 shows the general Pentium II processor specifications. Table 3.33 shows the specifications that vary by model for the models that have been introduced to date.
Table 3.32
Pentium II General Processor Specifications
Bus Speeds
66MHz, 100MHz
CPU clock multiplier
3.5x, 4x, 4.5x, 5x
CPU Speeds
233MHz, 266MHz, 300MHz, 333MHz, 350MHz, 400MHz, 450MHz
Cache Memory
16Kx2 (32KB) L1, 512KB 1/2-speed L2
Internal Registers
32-bit
External Data Bus
64-bit system bus w/ ECC; 64-bit cache bus w/ optional ECC
Memory Address Bus
36-bit
Addressable Memory
64GB
Virtual Memory
64TB
Physical package
Single Edge Contact Cartridge (S.E), 242 pins
Package Dimensions
5.505 in. (12.82cm)×2.473 inches (6.28cm)×0.647 in. (1.64cm)
Math coprocessor
Built-in FPU (floating-point unit)
Power management
SMM (System Management Mode)
Table 3.33
Pentium II Specifications by Model
Pentium II MMX Processor (350, 400 and 450MHz)
Introduction date
April 15, 1998
Clock speeds
350MHz (100MHz×3.5), 400MHz (100MHz ×4), and 450MHz
(100MHz×4.5)
iCOMP Index 2.0 rating
386 (350MHz), 440 (400MHz), and 483 (450MHz)
Number of transistors
7.5 million (0.25 micron process), plus 31 million in 512KB L2 cache
Cacheable RAM
4GB
Operating voltage
2.0v
Slot
Slot 2
Die Size
0.400 inches per side (10.2mm)
Mobile Pentium II Processor (266, 300, 333, and 366MHz)
Introduction date
January 25, 1999
Clock speeds
266, 300, 333, and 366MHz
Number of transistors
27.4 million (0.25 micron process), 256KB on-die L2 cache
Ball Grid Array (BGA)
Number of balls = 615
Dimensions
Width = 31mm; Length = 35mm
Core voltage
1.6 volts
Thermal design power
ranges by frequency
366MHz = 9.5 watts; 333MHz = 8.6 watts; 300MHz = 7.7 watts;
266MHz = 7.0 watts
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Pentium II MMX Processor (333MHz)
Introduction date
January 26, 1998
Clock speeds
333MHz (66MHz×5)
iCOMP Index 2.0 rating
366
Number of transistors
7.5 million (0.25 micron process), plus 31 million in 512KB L2 cache
Cacheable RAM
512MB
Operating voltage
2.0v
Slot
Slot 1
Die Size
0.400 inches per side (10.2mm)
Pentium II MMX Processor (300MHz)
Introduction date
May 7, 1997
Clock speeds
300MHz (66MHz×4.5)
iCOMP Index 2.0 rating
332
Number of transistors
7.5 million (0.35 micron process), plus 31 million in 512KB L2 cache
Cacheable RAM
512MB
Die Size
0.560 inches per side (14.2mm)
Pentium II MMX Processor (266MHz)
Introduction date
May 7, 1997
Clock speeds
266MHz (66MHz×4)
iCOMP Index 2.0 rating
303
Number of transistors
7.5 million (0.35 micron process), plus 31 million in 512KB L2 cache
Cacheable RAM
512MB
Slot
Slot 1
Die Size
0.560 inches per side (14.2mm)
Pentium II MMX Processor (233MHz)
Introduction date
May 7, 1997
Clock speeds
233MHz (66MHz×3.5)
iCOMP Index 2.0 rating
267
Number of transistors
7.5 million (0.35 micron process), plus 31 million in 512KB L2 cache
Cacheable RAM
512MB
Slot
Slot 1
Die Size
0.560 inches per side (14.2mm)
As you can see from the table, the Pentium II can handle up to 64GB of physical memory. Like
the Pentium Pro, the CPU incorporates Dual Independent Bus architecture. This means the chip
has two independent buses: one for accessing the L2 cache, the other for accessing main memory.
These dual buses can operate simultaneously, greatly accelerating the flow of data within the system. The L1 cache always runs at full core speeds because it is mounted directly on the processor
die. The L2 cache in the Pentium II normally runs at 1/2-core speed, which saves money and
allows for less expensive cache chips to be utilized. For example, in a 333MHz Pentium II, the L1
cache runs at a full 333MHz, while the L2 cache runs at 167MHz. Even though the L2 cache is
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not at full core speed as it was with the Pentium Pro, this is still far superior to having cache
memory on the motherboard running at the 66MHz motherboard speed of most Socket 7
Pentium designs. Intel claims that the DIB architecture in the Pentium II allows up to three times
the bandwidth of normal single-bus processors like the original Pentium.
By removing the cache from the processor’s internal package and using external chips mounted
on a substrate and encased in the cartridge design, Intel can now use more cost-effective cache
chips and more easily scale the processor up to higher speeds. The Pentium Pro was limited in
speed to 200MHz, largely due to the inability to find affordable cache memory that runs any
faster. By running the cache memory at 1/2-core speed, the Pentium II can run up to 400MHz
while still using 200MHz rated cache chips. To offset the 1/2-core speed cache used in the
Pentium II, Intel doubled the basic amount of integrated L2 cache from 256KB standard in the
Pro to 512KB standard in the Pentium II.
Note that the tag-RAM included in the L2 cache will allow up to 512MB of main memory to be
cacheable in PII processors from 233MHz to 333MHz. The 350MHz, 400MHz, and faster versions
include an enhanced tag-RAM that allows up to 4GB of main memory to be cacheable. This is
very important if you ever plan on adding more than 512MB of memory. In that case, you would
definitely want the 350MHz or faster version; otherwise, memory performance would suffer.
The system bus of the Pentium II provides “glueless” support for up to two processors. This
enables low-cost, two-way on the L2 cache bus. These system buses are designed especially for
servers or other mission-critical system use where reliability and data integrity are important. All
Pentium IIs also include parity-protected address/request and response system bus signals with a
retry mechanism for high data integrity and reliability.
To install the Pentium II in a system, a special processor-retention mechanism is required. This
consists of a mechanical support that attaches to the motherboard and secures the Pentium II
processor in Slot 1 to prevent shock and vibration damage. Retention mechanisms should be provided by the motherboard manufacturer. (For example, the Intel Boxed AL440FX and DK440LX
motherboards include a retention mechanism, plus other important system integration components.)
The Pentium II can generate a significant amount of heat that must be dissipated. This is accomplished by installing a heat sink on the processor. Many of the Pentium II processors will use an
active heat sink that incorporates a fan. Unlike heat sink fans for previous Intel boxed processors,
the Pentium II fans draw power from a three-pin power header on the motherboard. Most motherboards provide several fan connectors to supply this power.
Special heat sink supports are needed to furnish mechanical support between the fan heat sink
and support holes on the motherboard. Normally, a plastic support is inserted into the heat sink
holes in the motherboard next to the CPU, before installing the CPU/heat sink package. Most fan
heat sinks have two components: a fan in a plastic shroud and a metal heat sink. The heat sink is
attached to the processor’s thermal plate and should not be removed. The fan can be removed
and replaced if necessary, for example, if it has failed. Figure 3.43 shows the SEC assembly with
fan, power connectors, mechanical supports, and the slot and support holes on the motherboard.
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Heat Sink Support Mechanism
Single Edge Contact (S.E.C.) cartridge
Fan
Shroud Covering
Heat Sink Fins
Cable
Fan Power Connector
Heat Sink Retention Mechanism
Slot 1 Connector
Retention
Mechanism
Attach
Mount
Heat Sink Support Holes
Figure 3.43
Pentium II processor and heat sink assembly.
The following tables show the specifications unique to certain versions of the Pentium II
processor.
To identify exactly which Pentium II processor you have and what its capabilities are, look at the
specification number printed on the SEC cartridge. You will find the specification number in the
dynamic mark area on the top of the processor module. See Figure 3.44 to locate these markings.
After you have located the specification number (actually, it is an alphanumeric code), you can
look it up in Table 3.34 to see exactly which processor you have.
For example, a specification number of SL2KA identifies the processor as a Pentium II 333MHz
running on a 66MHz system bus, with an ECC L2 cache—and that this processor runs on only
2.0 volts. The stepping is also identified, and by looking in the Pentium II Specification Update
Manual published by Intel, you could figure out exactly which bugs were fixed in that revision.
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2-D Matrix Mark
intel pentium
II
with MMX™ technology
®
®
P R O C E S S O R
iCOMP® 2.0 index=YYY
SZNNN/XYZ ORDER CODE
XXXXXXXX-NNNN
Logo
Product Name
intel
Dynamic Mark Area
pentium ® II
®
Dynamic Mark Area
P R O C E S S O R
with MMX™ technology
Trademark
m c '94 '96
03.89719037 CH03
pentium ® II
P R O C E S S O R
!
intel
®
Logo
Figure 3.44
Table 3.34
Hologram
Location
Product Name
Pentium II single edge contact cartridge.
Basic Pentium II Processor Identification Information
CPUID
Core/Bus
Speed
(MHz)
L2 Cache
Size (MB)
L2 Cache
Type
CPU
Package
Notes
(see
foonotes)
C0
0633h
233/66
512
non-ECC
SECC 3.00
5
C0
0633h
266/66
512
non-ECC
SECC 3.00
5
SL268
C0
0633h
233/66
512
ECC
SECC 3.00
5
SL269
C0
0633h
266/66
512
ECC
SECC 3.00
5
SL28K
C0
0633h
233/66
512
non-ECC
SECC 3.00
1, 3, 5
SL28L
C0
0633h
266/66
512
non-ECC
SECC 3.00
1, 3, 5
S-spec
Core
Stepping
SL264
SL265
SL28R
C0
0633h
300/66
512
ECC
SECC 3.00
5
SL2MZ
C0
0633h
300/66
512
ECC
SECC 3.00
1, 5
SL2HA
C1
0634h
300/66
512
ECC
SECC 3.00
5
SL2HC
C1
0634h
266/66
512
non-ECC
SECC 3.00
5
SL2HD
C1
0634h
233/66
512
non-ECC
SECC 3.00
5
SL2HE
C1
0634h
266/66
512
ECC
SECC 3.00
5
SL2HF
C1
0634h
233/66
512
ECC
SECC 3.00
5
SL2QA
C1
0634h
233/66
512
non-ECC
SECC 3.00
1, 3, 5
SL2QB
C1
0634h
266/66
512
non-ECC
SECC 3.00
1, 3, 5
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S-spec
Core
Stepping
CPUID
Core/Bus
Speed
(MHz)
L2 Cache
Size (MB)
L2 Cache
Type
171
Chapter 3
CPU
Package
Notes
(see
foonotes)
SL2QC
C1
0634h
300/66
512
ECC
SECC 3.00
1, 5
SL2KA
dA0
0650h
333/66
512
ECC
SECC 3.00
5
1
SL2QF
dA0
0650h
333/66
512
ECC
SECC 3.00
SL2K9
dA0
0650h
266/66
512
ECC
SECC 3.00
SL35V
dA1
0651h
300/66
512
ECC
SECC 3.00
1, 2
SL2QH
dA1
0651h
333/66
512
ECC
SECC 3.00
1, 2
SL2S5
dA1
0651h
333/66
512
ECC
SECC 3.00
2, 5
SL2ZP
dA1
0651h
333/66
512
ECC
SECC 3.00
2, 5
SL2ZQ
dA1
0651h
350/100
512
ECC
SECC 3.00
2, 5
SL2S6
dA1
0651h
350/100
512
ECC
SECC 3.00
2, 5
SL2S7
dA1
0651h
400/100
512
ECC
SECC 3.00
2, 5
SL2SF
dA1
0651h
350/100
512
ECC
SECC 3.00
1, 2
SL2SH
dA1
0651h
400/100
512
ECC
SECC 3.00
1, 2
SL2VY
dA1
0651h
300/66
512
ECC
SECC 3.00
1, 2
SL33D
dB0
0652h
266/66
512
ECC
SECC 3.00
1, 2, 5
SL2YK
dB0
0652h
300/66
512
ECC
SECC 3.00
1, 2, 5
SL2WZ
dB0
0652h
350/100
512
ECC
SECC 3.00
1, 2, 5
SL2YM
dB0
0652h
400/100
512
ECC
SECC 3.00
1, 2, 5
SL37G
dB0
0652h
400/100
512
ECC
SECC2 OLGA
1, 2, 4
SL2WB
dB0
0652h
450/100
512
ECC
SECC 3.00
1, 2, 5
SL37H
dB0
0652h
450/100
512
ECC
SECC2 OLGA
1, 2
SL2KE
TdB0
1632h
333/66
512
ECC
PGA
2, 4
SL2W7
dB0
0652h
266/66
512
ECC
SECC 2.00
2, 5
SL2W8
dB0
0652h
300/66
512
ECC
SECC 3.00
2, 5
SL2TV
dB0
0652h
333/66
512
ECC
SECC 3.00
2, 5
SL2U3
dB0
0652h
350/100
512
ECC
SECC 3.00
2, 5
SL2U4
dB0
0652h
350/100
512
ECC
SECC 3.00
2, 5
SL2U5
dB0
0652h
400/100
512
ECC
SECC 3.00
2, 5
SL2U6
dB0
0652h
400/100
512
ECC
SECC 3.00
2, 5
SL2U7
dB0
0652h
450/100
512
ECC
SECC 3.00
2, 5
SL356
dB0
0652h
350/100
512
ECC
SECC2 PLGA
2, 5
SL357
dB0
0652h
400/100
512
ECC
SECC2 OLGA
2, 5
SL358
dB0
0652h
450/100
512
ECC
SECC2 OLGA
2, 5
SL37F
dB0
0652h
350/100
512
ECC
SECC2 PLGA
1, 2, 5
SL3FN
dB0
0652h
350/100
512
ECC
SECC2 OLGA
2, 5
SL3EE
dB0
0652h
400/100
512
ECC
SECC2 PLGA
2, 5
SL3F9
dB0
0652h
400/100
512
ECC
SECC2 PLGA
1, 2
SL38M
dB1
0653h
350/100
512
ECC
SECC 3.00
1, 2, 5
SL38N
dB1
0653h
400/100
512
ECC
SECC 3.00
1, 2, 5
(continues)
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Page 172
Microprocessor Types and Specifications
Continued
CPUID
Core/Bus
Speed
(MHz)
L2 Cache
Size (MB)
L2 Cache
Type
CPU
Package
Notes
(see
foonotes)
0653h
350/100
512
ECC
SECC 3.00
2, 5
dB1
0653h
400/100
512
ECC
SECC 3.00
2, 5
dB1
0653h
400/100
512
ECC
SECC2 OLGA
1, 2
S-spec
Core
Stepping
SL36U
dB1
SL38Z
SL3D5
SECC = Single Edge Contact Cartridge
SECC2 = Single Edge Contact Cartridge revision 2
PLGA = Plastic Land Grid Array
OLGA = Organic Land Grid Array
CPUID = The internal ID returned by the CPUID instruction
ECC = Error Correcting Code
1. This is a boxed Pentium II processor with an attached fan heat sink.
2. These processors have an enhanced L2 cache, which can cache up to 4GB of main memory. Other standard
PII processors can only cache up to 512MB of main memory.
3. These boxed processors may have packaging which incorrectly indicates ECC support in the L2 cache.
4. This is a boxed Pentium II OverDrive processor with an attached fan heat sink, designed for upgrading
Pentium Pro (Socket 8) systems.
5. These parts will only operate at the specified clock multiplier frequency ratio at which they were manufactured. They can only be overclocked by increasing bus speed.
The two variations of the SECC2 cartridge vary by the type of processor core package on the
board. The PLGA (Plastic Land Grid Array) is the older type of packaging used in previous SECC
cartridges as well, and is being phased out. Taking its place is the newer OLGA (Organic Land
Grid Array), which is a processor core package that is smaller and easier to manufacture. It also
allows better thermal transfer between the processor die and the heat sink, which is attached
directly to the top of the OLGA chip package. Figure 3.45 shows the open back side (where the
heat sink would be attached) of SECC2 processors with PLGA and OLGA cores.
PLGA
OLGA
Figure 3.45
SECC2 processors with PLGA and OLGA cores.
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Pentium II motherboards have an onboard voltage regulator circuit that is designed to power the
CPU. Currently, there are Pentium II processors that run at several different voltages, so the regulator must be set to supply the correct voltage for the specific processor you are installing. As
with the Pentium Pro and unlike the older Pentium, there are no jumpers or switches to set; the
voltage setting is handled completely automatically through the Voltage ID (VID) pins on the
processor cartridge. Table 3.35 shows the relationship between the pins and the selected voltage.
Table 3.35
Pentium II Voltage ID Definition
Processor Pins
VID4
VID3
VID2
VID1
VID0
Voltage
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
1.80
1.85
1.90
1.95
2.00
2.05
No CPU
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
1
0
0
0
0
3.5
0 = Processor pin connected to Vss
1 = Open on processor
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To ensure the system is ready for all Pentium II processor variations, the values in bold must be
supported. Most Pentium II processors run at 2.8v, with some newer ones at 2.0v.
The Pentium II Mobile Module is a Pentium II for notebooks that includes the North Bridge of
the high-performance 440BX chipset. This is the first chipset on the market that allows 100MHz
processor bus operation, although that is currently not supported in the mobile versions. The
440BX chipset was released at the same time as the 350 and 400MHz versions of the Pentium II;
it is the recommended minimum chipset for any new Pentium II motherboard purchases.
◊◊ See “Mobile Pentium II,” p. 1218.
Newer variations on the Pentium II include the Pentium IIPE, which is a mobile version that
includes 256KB of L2 cache directly integrated into the die. This means that it runs at full core
speed, making it faster than the desktop Pentium II, because the desktop chips use half-speed L2
cache.
Celeron
The Celeron processor is a P6 with the same processor core as the Pentium II. It is mainly
designed for lower cost PCs in the $1,000 or less price category. The best “feature” is that
although the cost is low, the performance is not. In fact, due to the superior cache design, the
Celeron outperforms the Pentium II at the same speed and at a lower cost.
Most of the features for the Celeron are the same as the Pentium II because it uses the same internal processor core. The main differences are in packaging and L2 cache design.
Up until recently, all Celeron processors were available in a package called the Single Edge
Processor Package (SEPP or SEP package). The SEP package is basically the same Slot 1 design as
the SECC (Single Edge Contact Cartridge) used in the Pentium II/III, with the exception of the
fancy plastic cartridge cover. This cover is deleted in the Celeron, making it cheaper to produce
and sell. Essentially the Celeron uses the same circuit board as is inside the Pentium II package.
√√ See “Single Edge Contact (SEC) and Single Edge Processor (SEP) Packaging,” p. 71.
Even without the plastic covers, the Slot 1 packaging was more expensive than it should be. This
was largely due to the processor retention mechanisms (stands) required to secure the processor
into Slot 1 on the motherboard, as well as the larger and more complicated heat sinks required.
This, plus competition from the lower end Socket 7 systems using primarily AMD processors, led
Intel to introduce the Celeron in a socketed form. The socket is called PGA-370 or Socket 370,
because it has 370 pins. The processor package designed for this socket is called the Plastic Pin
Grid Array (PPGA) package (see Figure 3.46). The PPGA package plugs into the 370 pin socket and
allows for lower cost, lower profile, and smaller systems because of the less expensive processor
retention and cooling requirements of the socketed processor.
√√ See “Socket PGA-370,” p. 85.
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intel®
PPGA Package
Figure 3.46
S.E.P. Package
Celeron processors in the PPGA and SEP packages.
All Celeron processors at 433MHz and lower have been available in the SEPP that plugs into the
242-contact slot connector. The 300MHz and higher versions are also available in the PPGA package. This means that the 300MHz–433MHz have been available in both packages, while the
466MHz and higher speed versions are only available in the PPGA.
Motherboards that include Socket 370 cannot accept Slot 1 versions of the Celeron, and would
also be unable to accept Pentium II or III processors. I normally recommend people use Slot 1
motherboards even for Celerons, because they can later upgrade to Pentium III processors without changing the board. That is because most motherboards that include a Slot 1 can accept
Pentium II, Pentium III, or SEPP (Slot 1 board type) Celeron processors. Since the newest and
fastest Celerons are only available in the socketed form, you would think this would make them
unusable in a Slot 1 motherboard. Fortunately, there are slot-to-socket adapters (usually called
slot-kets) available for about $10 that plug into Slot 1 and incorporate a Socket 370 on the card.
Figure 3.47 shows a typical slot-ket adapter.
Socket 370
Slot connector
Figure 3.47
Slot-ket adapter for installing PPGA processors in Slot 1 motherboards.
Highlights of the Celeron include
■ Available at 300MHz (300A) and higher core frequencies with 128KB L2 cache; 300MHz
and 266MHz core frequencies without L2 cache
■ Uses same P6 core processor as the Pentium Pro and Pentium II
■ Dynamic execution microarchitecture
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■ Operates on a 66MHz CPU bus (future versions will likely also use the 100MHz bus)
■ Specifically designed for lower cost value PC systems
■ Includes MMX technology
■ More cost-effective packaging technology including Single Edge Processor (SEP) or Plastic
Pin Grid Array (PPGA) packages
■ Integrated 32KB L1 cache, implemented as separate 16KB instruction and 16KB data caches
■ Integrated thermal diode for temperature monitoring
Table 3.36 shows the specifications for all the Celeron processors.
Table 3.36
Intel Celeron Processor Specifications
Intel Celeron Processor (466MHz)
Introduction date
April 26, 1999
Clock speeds
466MHz
Number of transistors
19 million (0.25 micron process)
Cache: 128KB on-die packaging
Plastic Pin Grid Array (PPGA), 370 pins
Bus Speed
66MHz
Bus Width
64-bit system bus
Addressable Memory
4GB
Typical Use
Value PCs
Mobile Intel Celeron Processor (366MHz)
Introduction date
May 17, 1999
Clock speeds
366MHz
Number of transistors
18.9 million (0.25 micron process), 128KB on-die L2 cache
Ball Grid Array (BGA) number of balls
615
Dimensions
Width = 32mm; Length = 37mm
Core voltage
1.6 volts
Thermal design power
300MHz = 8.6 watts
Typical use
Value/low-cost mobile PCs
Mobile Intel Celeron Processor (333MHz)
Introduction date
April 5, 1999
Clock speeds
333MHz
Number of transistors
18.9 million (0.25 micron process), 128KB on-die L2 cache
Ball Grid Array (BGA) number of balls
615
Dimensions
Width = 31mm; Length = 35mm
Core voltage
1.6 volts
Thermal design power
300MHz = 8.6 watts
Typical use
Value/low-cost mobile PCs
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Intel Celeron Processor (433MHz)
Introduction date
March 22, 1999
Clock speeds
433MHz
Number of transistors
19 million (0.25 micron process)
Cache
128KB on-die Single Edge Processor Package (SEPP), 242 pins
Plastic Pin Grid Array (PPGA)
370 pins
Bus Speed
66MHz
Bus Width
64 bit system bus
Addressable Memory
4GB
Typical Use
Value PCs
Mobile Intel Celeron Processor (266 and 300MHz)
Introduction date
January 25, 1999
Clock speeds
266 and 300MHz
Number of transistors
18.9 million (0.25 micron process), 128KB on-die L2 cache
Ball Grid Array (BGA) number of balls
615
Dimensions
Width = 31mm; Length = 35mm
Core voltage
1.6 volts
Thermal design power
300MHz = 7.7 watts; 266MHz = 7.0 watts
Typical use
Value/low-cost mobile PCs
Intel Celeron Processor (400, 366MHz)
Introduction date
January 4, 1999
Clock speeds
400, 366MHz
Number of transistors
19 million (0.25 micron process)
Single Edge Processor Package (SEPP)
242 pins
Plastic Pin Grid Array (PPGA)
370 pins
Bus Speed
66MHz
Bus Width
64-bit system bus
Addressable Memory
4GB
Typical Use
Low-cost PCs
Intel Celeron Processor (333MHz)
Introduction date
August 24, 1998
Clock speeds
333MHz
Number of transistors
19 million (0.25 micron process)
Single Edge Processor Package (SEPP)
242 pins
Bus Speed
66MHz
Bus Width
64-bit system bus
Addressable Memory
4GB
Package Dimensions
5” × 2.275” × .208”
Typical Use
Low-cost PCs
(continues)
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Continued
Intel Celeron Processor (300A-MHz)
Introduction date
August 24, 1998
Clock speeds
300MHz
Number of transistors
19 million (0.25 micron process)
Single Edge Processor Package (SEPP)
242 pins
Bus Speed
66MHz
Bus Width
64-bit system bus
Addressable Memory
4GBs
Package Dimensions
5” × 2.275” × .208”
Typical Use
Low-cost PCs
Intel Celeron Processor (300 MHz)
Introduction date
June 8, 1998
Clock speeds
300 MHz
Number of transistors
7.5 million (0.25 micron process)
Single Edge Processor Package (SEPP)
242 pins
Bus Speed
66MHz
Bus Width
64-bit system bus
Addressable Memory
4GB
Virtual Memory
64TB
Package Dimensions
5” × 2.275” × .208”
Typical Use
Low-cost PCs
Intel Celeron Processor (266MHz)
Introduction date
April 15, 1998
Clock speeds
266MHz
Number of transistors
7.5 million (0.25 micron process)
Single Edge Processor Package (SEPP)
242 pins
Bus Speed
66MHz
Bus Width
64-bit system bus
Addressable Memory
4GB
Virtual Memory
64TB
Package Dimensions
5” × 2.275” × .208”
Typical Use
Low-cost PCs
The Intel Celeron processors at 466, 433, 400, 366, 333, and 300A-MHz include integrated L2
cache 128KB. The core for the 466, 433, 400, 366, 333, and 300A-MHz processors have a whopping 19 million transistors due to the addition of the integrated 128KB L2 cache.
All the Celerons are manufactured using the .25 micron process, which reduces processor heat
and enables the Intel Celeron processor to use a smaller heat sink compared to some of the
Pentium II processors. Table 3.37 shows the power consumed by the various Celeron processors.
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Table 3.37
179
Intel Celeron Processor Power Consumption
Processor Speed
Current
(amps)
Voltage
Watts
266MHz
300MHz
300A-MHz
333MHz
366MHz
400MHz
433MHz
466MHz
8.2
9.3
9.3
10.1
11.2
12.2
12.6
13.4
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
16.4
18.6
18.6
20.2
22.4
24.4
25.2
26.8
Figure 3.48 shows the Intel Celeron processor identification information. Figure 3.49 shows the
Celeron’s PPGA processor markings.
Static White Silkscreen marks
intel
celeron™
®
im©98
FFFFFFFF SYYYY
266/66 COA
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Dynamic laser mark area
Figure 3.48
Celeron SEPP (Single Edge Processor Package) processor markings.
Note
The markings on the processor identify the following information:
SYYYY = S-spec. number
FFFFFFFF = FPO # (test lot tracability #)
COA = Country of assembly
Top
Bottom
intel®
celeron™
AAAAAAAZZZ
LLL SYYYY
¡
Figure 3.49
Celeron PPGA processor markings.
Country of Origin
FFFFFFFF-XXXX
M C ‘98
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Note
The PPGA processor markings identify the following information:
AAAAAAA = Product pode
ZZZ = Processor speed (MHz)
LLL = Integrated L2 cache size (in Kilobytes)
SYYYY = S-spec. number
FFFFFFFF-XXXX = Assembly lot tracking number
Table 3.38 shows all the available variations of the Celeron, indicated by the S-specification
number.
Table 3.38
Intel Celeron Variations
S-spec
Core
Stepping
L2 Size
CPUID
Speed
Core/Bus
Package
SL2SY
dA0
0
0650h
266/66MHz
SEPP
SL2YN
dA0
0
0650h
266/66MHz
SEPP
SL2YP
dA0
0
0650h
300/66MHz
SEPP
SL2Z7
dA0
0
0650h
300/66MHz
SEPP
SL2TR
dA1
0
0651h
266/66MHz
SEPP
SL2QG
dA1
0
0651h
266/66MHz
SEPP
SL2X8
dA1
0
0651h
300/66MHz
SEPP
SL2Y2
dA1
0
0651h
300/66MHz
SEPP
1
SL2Y3
dB0
0
0652h
266/66MHz
SEPP
1
SL2Y4
dB0
0
0652h
300/66MHz
SEPP
1
SL2WM
mA0
128KB
0660h
300A/66MHz
SEPP
3
SL32A
mA0
128KB
0660h
300A/66MHz
SEPP
1
SL2WN
mA0
128KB
0660h
333/66MHz
SEPP
3
SL32B
mA0
128KB
0660h
333/66MHz
SEPP
1
SL376
mA0
128KB
0660h
366/66MHz
SEPP
SL37Q
mA0
128KB
0660h
366/66MHz
SEPP
SL39Z
mA0
128KB
0660h
400/66MHz
SEPP
SL37V
mA0
128KB
0660h
400/66MHz
SEPP
SL3BC
mA0
128KB
0660h
433/66MHz
SEPP
SL35Q
mB0
128KB
0665h
300A/66MHz
PPGA
SL36A
mB0
128KB
0665h
300A/66MHz
PPGA
SL35R
mB0
128KB
0665h
333/66MHz
PPGA
SL36B
mB0
128KB
0665h
333/66MHz
PPGA
SL36C
mB0
128KB
0665h
366/66MHz
PPGA
SL35S
mB0
128KB
0665h
366/66MHz
PPGA
SL3A2
mB0
128KB
0665h
400/66MHz
PPGA
Notes (see
foonotes)
1
1
1
1
1
2
2
2
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S-spec
Core
Stepping
L2 Size
CPUID
Speed
Core/Bus
Chapter 3
Package
Notes (see
foonotes)
2
SL37X
mB0
128KB
0665h
400/66MHz
PPGA
SL3BA
mB0
128KB
0665h
433/66MHz
PPGA
SL3BS
mB0
128KB
0665h
433/66MHz
PPGA
SL3EH
mB0
128KB
0665h
466/66MHz
PPGA
SL3FL
mB0
128KB
0665h
466/66MHz
PPGA
181
2
2
SEPP = Single Edge Processor Package
PPGA = Plastic Pin Grid Array
1. Boxed processor with an attached fan heat sink
2. Boxed processor with an unattached fan heat sink
3. Also available as a boxed processor with an attached fan heat sink
Pentium III
The Pentium III processor, shown in Figure 3.50, was released in February 1999 and introduced
several new features to the P6 family. The most important advancements are the streaming SIMD
extensions (SSE), consisting of 70 new instructions that dramatically enhance the performance
and possibilities of advanced imaging, 3D, streaming audio, video, and speech-recognition applications.
Figure 3.50
Pentium III processor. Photograph used by permission of Intel Corporation.
Based on Intel’s advanced 0.25 micron CMOS process technology, the PIII core has over 9.5 million transistors. The Pentium III is available in 450MHz, 500MHz, and 550MHz versions, as well
as in 500MHz and 550MHz Xeon versions. The Pentium III also incorporates advanced features
such as a 32KB L1 cache and half core speed 512KB L2 cache with cacheability for up to 4GB of
addressable memory space. The PIII also can be used in dual-processing systems with up to 64GB
of physical memory. A self-reportable processor serial number gives security, authentication, and
system management applications a powerful new tool for identifying individual systems.
Pentium III processors are available in Intel’s Single Edge Contact Cartridge 2 (SECC2) form factor, which is replacing the more expensive older SEC packaging. The SECC2 package covers only
one side of the chip, and allows for better heat sink attachment and less overall weight. It is also
less expensive.
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Architectural features of the Pentium III processor include
■ Streaming SIMD Extensions. Seventy new instructions for dramatically faster processing and
improved imaging, 3D streaming audio and video, Web access, speech recognition, new
user interfaces, and other graphics and sound rich applications.
■ Intel Processor Serial Number. The processor serial number, the first of Intel’s planned building blocks for PC security, serves as an electronic serial number for the processor and, by
extension, its system or user. This enables the system/user to be identified by networks and
applications. The processor serial number will be used in applications that benefit from
stronger forms of system and user identification, such as the following:
• Applications using security capabilities. Managed access to new Internet content and services; electronic document exchange
• Manageability applications. Asset management; remote system load and configuration
• Intel MMX Technology
• Dynamic Execution Technology
• Incorporates an on-die diode. This can be used to monitor the die temperature for thermal management purposes.
Most of the Pentium III processors will be made in the improved SECC2 packaging, which is less
expensive to produce and allows for a more direct attachment of the heat sink to the processor
core for better cooling.
All Pentium III processors have 512KB of L2 cache, which runs at half of the core processor
speed. Xeon versions have 512KB, 1MB, or 2MB of L2 cache that runs at full core speed. These
are more expensive versions designed for servers and workstations.
All PIII processor L2 caches can cache up to 4GB of addressable memory space, and include Error
Correction Code (ECC) capability.
Table 3.39 shows the Pentium III specifications by model.
Table 3.39
Pentium III Processor Specifications
Pentium III Processor (550MHz)
Introduction date
May 17, 1999
Clock Speeds
450, 500MHz
Number of transistors
9.5 million (0.25 micron process)
L2 cache
512KB
Processor Package Style
Single Edge Contact (SEC) Cartridge 2
System Bus Speed
100MHz
System Bus Width
64-bit system bus
Addressable Memory
64GB
Typical Use
Business and consumer PCs, one- and two-way servers and workstations
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Pentium III Processor (450 and 500MHz)
Introduction date
February 26, 1999
Clock Speeds
450, 500MHz
Number of transistors
9.5 million (0.25 micron process)
L2 cache
512KB
Processor Package Style
Single Edge Contact (SEC) Cartridge 2
System Bus Speed
100MHz
System Bus Width
64-bit system bus
Addressable Memory
64GB
Typical Use
Business and consumer PCs, one- and two-way servers and workstations
Pentium III processors can be identified by their markings, which are found on the top edge of
the processor cartridge. Figure 3.51 shows the format and meaning of the markings.
2-D Matrix Mark
Speed/Cache/Bus/Voltage
UL Identifier
Dynamic Mark Area
FPO- Serial # Country
of Assy
500/512/100/2.0V S1
FFFFFFFF-NNNN XXXXX
i m C '98 SYYYY
pentium ®
S-Spec
Processor Markings
intel
®
Hologram
Location
Figure 3.51
Pentium III processor markings.
Table 3.40 shows the available variations of the Pentium III, indicated by the S-specification
number.
Table 3.40
Intel Pentium III Processor Variations
CPUID
Core/Bus
Speed
(MHz)
L2 Cache
Size
L2 Cache
Type
Package
672
450/100
512
ECC
SECC2
kB0
672
500/100
512
ECC
SECC2
kB0
672
450/100
512
ECC
SECC2
S-Spec
Core
Stepping
SL364
kB0
SL365
SL3CC
Notes
(see
footnotes)
1
(continues)
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Continued
CPUID
Core/Bus
Speed
(MHz)
L2 Cache
Size
L2 Cache
Type
Package
Notes
(see
footnotes)
672
500/100
512
ECC
SECC2
1
kB0
672
450/100
512
ECC
SECC
kB0
672
500/100
512
ECC
SECC
SL35D
kC0
673
450/100
512
ECC
SECC2
SL35E
kC0
673
500/100
512
ECC
SECC2
SL3F7
kC0
673
550/100
512
ECC
SECC2
S-Spec
Core
Stepping
SL3CD
kB0
SL38E
SL38F
SECC = Single Edge Contact Cartridge
SECC2 = Single Edge Contact Cartridge revision 2
CPUID = The internal ID returned by the CPUID instruction
ECC = Error Correcting Code
1. This is a boxed processor with an attached heat sink
Pentium III processors are all clock multiplier locked. This is a means to prevent processor fraud
and overclocking by making the processor work only at a given clock multiplier. Unfortunately,
this feature can be bypassed by making modifications to the processor under the cartridge cover,
and unscrupulous individuals have been selling lower speed processors remarked as higher
speeds. It pays to purchase your systems or processors from direct Intel distributors or high-end
dealers that do not engage in these practices.
Pentium II/III Xeon
The Pentium II and III processors are available in special high-end versions called Xeon processors. These differ from the standard Pentium II and III in three ways: packaging, cache size, and
cache speed.
Xeon processors use a larger SEC (Single Edge Contact) cartridge than the standard PII/III processors, mainly to house a larger internal board with more cache memory. The Xeon processor is
shown in Figure 3.52; the Xeon’s SEC is shown in Figure 3.53.
Figure 3.52
Pentium III Xeon processor. Photograph used by permission of Intel.
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Plastic Enclosure
Primary Side Substrate
Processor and Cache
Primary Side Substrate
Thermal Plate Retention Clips
Pin Fasteners
Aluminum Thermal Plate
Figure 3.53
Xeon processor internal components.
Besides the larger package, the Xeon processors also include more L2 cache. They are available in
three variations, with 512KB, 1MB, or 2MB of L2 cache. This cache is costly; the list price of the
2MB version is over $3,000!
Even more significant than the size of the cache is its speed. All the cache in the Xeon processors
run at the full core speed. This is difficult to do considering that the cache chips are separate
chips on the board; they are not integrated into the processor die like the Celeron. With the
amount of cache, that would be impossible today but might be possible in the future.
Table 3.41 shows the Xeon processor specifications for each model.
Table 3.41
Intel Pentium II and III Xeon Specifications
Pentium III Xeon Processor (500 and 550MHz)
Introduction date
March 17, 1999
Clock Speeds
500, 550MHz
Number of transistors
9.5 million (0.25 micron process)
L2 cache
512KB, 1 and 2MB for 500MHz
Processor Package Style
Single Edge Contact (SEC) Cartridge 2
System Bus Speed
100MHz
System Bus Width
64-bit system bus
Addressable Memory
64GB
Typical Use
Business PCs, two-, four- and eight-way (and higher) servers and
workstations
(continues)
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Continued
Pentium II Xeon Processor (450MHz)
Introduction date
January 5, 1999
Clock speed
450MHz
L2 cache
512KB, 1MB, and 2MB
Number of transistors
7.5 million
Processor Package Style
Single Edge Contact (SEC) Cartridge
System Bus Speed
100MHz
System Bus Width
8 bytes
Addressable Memory
64GB
Virtual Memory
64TB
Package Dimensions
Height 4.8” × Width 6.0” × Depth .73”
Typical Use
Four-way servers and workstations
Pentium II Xeon Processor (450MHz)
Introduction date
October 6, 1998
Clock speed
450MHz
L2 cache
512KB
Number of transistors
7.5 million
Processor Package Style
Single Edge Contact (SEC) Cartridge
System Bus Speed
100MHz
System Bus Width
8 bytes
Addressable Memory
64GB
Virtual Memory
64TB
Package Dimensions
Height 4.8” × Width 6.0” × Depth .73”
Typical Use
Dual-processor workstations and servers
Pentium II Xeon Processor (400MHz)
Introduction date
June 29, 1998
Clock speed
400MHz
L2 cache versions
512KB and 1MB
Number of transistors
7.5 million
Processor Package Style
Single Edge Contact (SEC) Cartridge
System Bus Speed
100MHz
System Bus Width
8 bytes
Addressable Memory
64GB
Virtual Memory
64TB
Package Dimensions
Height 4.8” × Width 6.0” × Depth .73”
Typical Use
Midrange and higher servers and workstations
Note that the Slot 2 Xeon processors do not replace the Slot 1 processors. Xeon processors for
Slot 2 are targeted at the mid-range to high-end server and workstation market segments, offering
larger, full-speed L2 caches and four-way multiprocessor support. Pentium III processors for Slot 1
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will continue to be the processor used in the business and home desktop market segments, and
for entry-level servers and workstations (single and dual processor systems).
Pentium III Future
There are several new developments on target for the Pentium III processors. The primary trend
seems to be the integration of L2 cache into the processor die, which also means it runs at full
core speed.
There will also be further reductions in the process size used to manufacture the processors.
Pentium II processors at 333MHz and up were the first members of the Pentium II processor family to be based on the “Deschutes” core (0.25 micron technology). Currently, through the
Pentium III 550, they are still using a 0.25 micron process, but will be shifting to a 0.18, and then
0.13 micron process in the future. The shift to the 0.13 micron process will also include a shift
from aluminum interconnects on the chip die to copper instead.
Other Sixth-Generation Processors
Besides Intel, many other manufacturers are now making P6 type processors, but often with a difference. Most of them are designed to interface with P5 class motherboards and for the lower end
markets. AMD has recently offered up the K7, which is a true sixth-generation design using its
own proprietary connection to the system.
This section examines the various sixth-generation processors from manufacturers other than
Intel.
Nexgen Nx586
Nexgen was founded by Thampy Thomas who hired some of the people formerly involved with
the 486 and Pentium processors at Intel. At Nexgen, they created the Nx586, a processor that was
functionally the same as the Pentium but not pin compatible. As such, it was always supplied
with a motherboard; in fact, it was normally soldered in. Nexgen did not manufacture the chips
or the motherboards they came in; for that they hired IBM Microelectronics. Later Nexgen was
bought by AMD, right before they were ready to introduce the Nx686, a greatly improved design
done by Greg Favor, and a true competitor for the Pentium. AMD took the Nx686 design and
combined it with a Pentium electrical interface to create a drop-in Pentium compatible chip
called the K6, which actually outperformed the original from Intel.
The Nx586 had all the standard fifth-generation processor features, such as superscalar execution
with two internal pipelines and a high performance integral L1 cache with separate code and
data caches. One advantage is that the Nx586 includes separate 16KB instruction and 16KB data
caches compared to 8KB each for the Pentium. These caches keep key instruction and data close
to the processing engines to increase overall system performance.
The Nx586 also included branch prediction capabilities, which are one of the hallmarks of a
sixth-generation processor. Branch prediction means the processor has internal functions to predict program flow to optimize the instruction execution.
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The Nx586 processor also featured an RISC (Reduced Instruction Set Computer) core. A translation unit dynamically translates x86 instructions into RISC86 instructions. These RISC86 instructions were specifically designed with direct support for the x86 architecture while obeying RISC
performance principles. They are thus simpler and easier to execute than the complex x86
instructions. This type of capability is another feature normally found only in P6 class processors.
The Nx586 was discontinued after the merger with AMD, who then took the design for the successor Nx686 and released it as the AMD-K6.
AMD-K6 Series
The AMD-K6 processor is a high-performance sixth-generation processor that is physically installable in a P5 (Pentium) motherboard. It was essentially designed for them by Nexgen, and was
first known as the Nx686. The Nexgen version never appeared because they were purchased by
AMD before the chip was due to be released. The AMD-K6 delivers performance levels somewhere
between the Pentium and Pentium II processor due to its unique hybrid design. Because it is
designed to install in Socket 7, which is a fifth-generation processor socket and motherboard
design, it cannot perform quite as a true sixth-generation chip because the Socket 7 architecture
severely limits cache and memory performance. However, with this processor, AMD is giving
Intel a lot of competition in the low- to mid-range market, where the Pentium is still popular.
The K6 processor contains an industry-standard, high-performance implementation of the new
multimedia instruction set (MMX), enabling a high level of multimedia performance. The K6-2
introduced an upgrade to MMX AMD calls 3DNow, which adds even more graphics and sound
instructions. AMD designed the K6 processor to fit the low-cost, high-volume Socket 7 infrastructure. This enables PC manufacturers and resellers to speed time to market and deliver systems
with an easy upgrade path for the future. AMD’s state-of-the-art manufacturing facility in Austin,
Texas (Fab 25) makes the AMD-K6 series processors. Initially they used AMD’s 0.35 micron, fivemetal layer process technology; newer variations use the 0.25 micron processor to increase production quantities because of reduced die size, as well as to decrease power consumption.
AMD-K6 processor technical features include
■ Sixth-generation internal design, fifth-generation external interface
■ Internal RISC core, translates x86 to RISC instructions
■ Superscalar parallel execution units (seven)
■ Dynamic execution
■ Branch prediction
■ Speculative execution
■ Large 64KB L1 cache (32KB instruction cache plus 32KB write-back dual-ported data cache)
■ Built-in floating-point unit (FPU)
■ Industry-standard MMX instruction support
■ System Management Mode (SMM)
■ Ceramic Pin Grid Array (CPGA) Socket 7 design
■ Manufactured using a 0.35 micron and 0.25 micron, five-layer design
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The K6-2 adds
■ Higher clock speeds
■ Higher bus speeds of up to 100MHz (Super7 motherboards)
■ 3DNow; 21 new graphics and sound processing instructions
The K6-3 adds
■ 256KB of on-die full core speed L2 cache
The addition of the full speed L2 cache in the K6-3 is significant. It brings the K6 series to a level
where it can fully compete with the Intel Celeron and Pentium II processors. The 3DNow capability added in the K6-2/3 is also being exploited by newer graphics programs, making these processors ideal for lower cost gaming systems.
The AMD-K6 processor architecture is fully x86 binary code compatible, which means it runs all
Intel software, including MMX instructions. To make up for the lower L2 cache performance of
the Socket 7 design, AMD has beefed up the internal L1 cache to 64KB total, twice the size of the
Pentium II or III. This, plus the dynamic execution capability, allows the K6 to outperform the
Pentium and come close to the Pentium II in performance for a given clock rate. The K6-3 is even
better with the addition of full core speed L2 cache.
Both the AMD-K5 and AMD-K6 processors are Socket 7 bus-compatible. However, certain modifications might be necessary for proper voltage setting and BIOS revisions. To ensure reliable operation of the AMD-K6 processor, the motherboard must meet specific voltage requirements.
The AMD processors have specific voltage requirements. Most older split-voltage motherboards
default to 2.8v Core/3.3v I/O, which is below specification for the AMD-K6 and could cause
erratic operation. To work properly, the motherboard must have Socket 7 with a dual-plane voltage regulator supplying 2.9v or 3.2v (233MHz) to the CPU core voltage (Vcc2) and 3.3v for the
I/O (Vcc3). The voltage regulator must be capable of supplying up to 7.5A (9.5A for the 233MHz)
to the processor. When used with a 200MHz or slower processor, the voltage regulator must
maintain the core voltage within 145 mv of nominal (2.9v+/-145 mv). When used with a
233MHz processor, the voltage regulator must maintain the core voltage within 100 mv of nominal (3.2v+/-100 mv).
If the motherboard has a poorly designed voltage regulator that cannot maintain this performance, unreliable operation can result. If the CPU voltage exceeds the absolute maximum voltage range, the processor can be permanently damaged. Also note that the K6 can run hot. Ensure
your heat sink is securely fitted to the processor and the thermally conductive grease or pad is
properly applied.
The motherboard must have an AMD-K6 processor-ready BIOS with support for the K6 built in.
Award has that support in their March 1, 1997 or later BIOS, AMI had K6 support in any of their
BIOS with CPU Module 3.31 or later, and Phoenix supports the K6 in version 4.0, release 6.0, or
release 5.1 with build dates of 4/7/97 or later.
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Because these specifications can be fairly complicated, AMD keeps a list of motherboards that
have been verified to work with the AMD-K6 processor on their Web site. All the motherboards
on that list have been tested to work properly with the AMD-K6. So, unless these requirements
can be verified elsewhere, it is recommended that you only use a motherboard from that list with
the AMD-K6 processor.
The multiplier, bus speed, and voltage settings for the K6 are shown in Table 3.42. You can identify which AMD-K6 you have by looking at the markings on this chip, as shown in Figure 3.57.
Table 3.42
AMD-K6 Processor Speeds and Voltages
Processor
Core
Speed
Clock
Multiplier
K6-III
450MHz
4.5x
100MHz
2.4v
3.3v
K6-III
400MHz
4x
100MHz
2.4v
3.3v
K6-2
475MHz
5x
95MHz
2.4v
3.3v
K6-2
450MHz
4.5x
100MHz
2.4v
3.3v
K6-2
400MHz
4x
100MHz
2.2v
3.3v
K6-2
380MHz
4x
95MHz
2.2v
3.3v
K6-2
366MHz
5.5x
66MHz
2.2v
3.3v
K6-2
350MHz
3.5x
100MHz
2.2v
3.3v
K6-2
333MHz
3.5x
95MHz
2.2v
3.3v
K6-2
333MHz
5.0x
66MHz
2.2v
3.3v
K6-2
300MHz
3x
100MHz
2.2v
3.3v
K6-2
300MHz
4.5x
66MHz
2.2v
3.3v
K6-2
266MHz
4x
66MHz
2.2v
3.3v
K6
300MHz
4.5x
66MHz
2.2v
3.45v
K6
266MHz
4x
66MHz
2.2v
3.3v
K6
233 MHz
3.5x
66MHz
3.2v
3.3v
K6
200MHz
3x
66MHz
2.9v
3.3v
K6
166MHz
2.5x
66MHz
2.9v
3.3v
AMD
Name
Voltage
Major Revision
Date Code
Copyright
AMD-K6-233APR
3.3V CORE/3.3V I/O
C 9710APB
m c 1997 AMD
Designed for
Microsoft™
Windows™95
MALAY
Microsoft Logo
Core
Voltage
I/O
Voltage
OPN
AMD-K6-233APR
AMD-K6™
AAAAA
Figure 3.54
Bus
Speed
I
Top Mark
AMD-K6 processor markings.
Case Temperature
R=0˚C-70˚C
Operating Voltage
P=3.2V-3.4V (Core) /3.3135V-3.6V (I/O)
Package Type
A=321-pin CPGA
Performance Rating
-233
Family Core
AMD-K6
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Older motherboards achieve the 3.5x setting by setting jumpers for 1.5x. The 1.5x setting for
older motherboards equates to a 3.5x setting for the AMD-K6 and newer Intel parts. To get the 4x
and higher setting requires a motherboard that controls three BF (bus frequency) pins, including
BF2. Older motherboards can only control two BF pins. The settings for the multipliers are shown
in Table 3.43.
Table 3.43
AMD-K6 Multiplier Settings
Multiplier
Setting
BF0
BF1
BF2
2.5x
Low
Low
High
3x
High
Low
High
3.5x
High
High
High
4x
Low
High
Low
4.5x
Low
Low
Low
5x
High
Low
Low
5.5x
High
High
Low
These settings are normally controlled by jumpers on the motherboard. Consult your motherboard documentation to see where they are and how to set them for the proper multiplier and
bus speed settings.
Unlike Cyrix and some of the other Intel competitors, AMD is a manufacturer and a designer.
This means they design and build their chips in their own fabs. Like Intel, AMD is migrating to
0.25 micron process technology and beyond. The original K6 has 8.8 million transistors and is
built on a 0.35 micron, five-layer process. The die is 12.7mm on each side, or about 162 square
mm. The K6-3 uses a 0.25 micron process and now incorporates 21.3 million transistors on a die
only 10.9mm on each side, or about 118 square mm. Further process improvements will enable
even more transistors, smaller die, higher yields, and greater numbers of processors. AMD has
recently won contracts with several high-end system suppliers, which gives them an edge on the
other Intel competitors. AMD has delivered more than 50 million Windows-compatible CPUs in
the last five years.
Because of its performance and compatibility with the Socket 7 interface, the K6 series is often
looked at as an excellent processor upgrade for motherboards currently using older Pentium or
Pentium MMX processors. Although they do work in Socket 7, the AMD-K6 processors have different voltage and bus speed requirements than the Intel processors. Before attempting any
upgrades, you should check the board documentation or contact the manufacturer to see if your
board will meet the necessary requirements. In some cases, a BIOS upgrade will also be necessary.
3DNow
3DNow technology was introduced in May 1998 in the K6-2 as a set of instructions that extend
the multimedia capabilities of the AMD chips. This allows greater performance for 3D graphics,
multimedia, and other floating-point-intensive PC applications.
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3DNow technology is a set of 21 instructions that use SIMD (Single Instruction Multiple Data)
techniques to operate on arrays of data rather than single elements. Positioned as an extension to
MMX technology, 3DNow is similar to the SSE (streaming SIMD extensions) found in the
Pentium III processors from Intel. SSE consists of 70 new SIMD type instructions.
3DNow is well supported by software including Microsoft Windows 95/98, Windows NT 4.0, and
all newer Microsoft operating systems. Application programming interfaces such as Microsoft’s
DirectX 6.x API and SGI’s Open GL API have been optimized for 3DNow technology, as have the
drivers for many leading 3D graphic accelerator suppliers, including 3Dfx, ATI, Matrox, and
nVidia.
AMD-K7
The K7 is AMD’s successor to the K6 series. The K7 is a whole new chip from the ground up and
does not interface via the Socket 7 or Super7 sockets like their previous chips. Instead AMD seems
to be taking a lesson from Intel, as the K7 looks almost exactly like a Pentium II/III cartridge.
Unfortunately it doesn’t plug into the same motherboards as the Pentium II/III; instead the K7
slot is a proprietary design requiring specific K7 motherboards with specific K7 chipsets.
The K7 is available in speeds from 550MHz and up, and uses a sideways 200MHz bus called the
EV6 to connect to the motherboard North Bridge chip as well as other processors. Licensed from
Digital Equipment, the EV6 bus is the same as that used for the Alpha 21264 processor, now
owned by Compaq.
The K7 has a very large 128KB of L1 cache on the processor die, and 200MHz L2 cache from
512KB to 8MB in the cartridge. As expected, the K7 has support for MMX and 3DNow instructions, but not for the newer SSE (streaming SIMD extensions) instructions from Intel.
The initial production will utilize 0.25 micron technology, and clock speeds will exceed 500MHz.
Subsequent versions will use a 0.18 micron process, and speeds will continue to increase. AMD
chairman and CEO William J. (Jerry) Sanders III has previously stated the goal of delivering 1GHz
K7 chips by 2000, utilizing copper interconnect manufacturing.
Cyrix MediaGX
The Cyrix MediaGX is designed for low-end sub-$1,000 retail store systems that must be highly
integrated and low priced. The MediaGX integrates the sound, graphics, and memory control by
putting these functions directly within the processor. With all these functions pulled “on chip,”
MediaGX-based PCs are priced lower than other systems with similar features.
The MediaGX processor integrates the PCI interface, coupled with audio, graphics, and memory
control functions, right into the processor unit. As such, a system with the MediaGX doesn’t
require a costly graphics or sound card. Not only that, but on the motherboard level, the
MediaGX and its companion chip replace the processor, North and South Bridge chips, the memory control hardware, and L2 cache found on competitive Pentium boards. Finally, the simplified
PC design of the MediaGX, along with its low-power and low-heat characteristics, allow the OEM
PC manufacturer to design a system in a smaller form factor with a reduced power-supply
requirement.
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The MediaGX processor is not a Socket 7 processor; in fact, it does not go in a socket at all—it is
permanently soldered into its motherboard. Because of the processor’s high level of integration,
motherboards supporting MediaGX processors and its companion chip (Cx5510) are of a different design than conventional Pentium boards. As such, a system with the MediaGX processor is
more of a disposable system than an upgradable system. You will not be able to easily upgrade
most components in the system, but that is often not important in the very low-end market. If
upgradability is important, look elsewhere. On the other hand, if you need the lowest-priced system possible, one with the MediaGX might fill the bill.
The MediaGX is fully Windows-compatible and will run the same software as an equivalent
Pentium. You can expect a MediaGX system to provide equivalent performance as a given
Pentium system at the same megahertz. The difference with the MediaGX is that this performance level is achieved at a much lower cost. Because the MediaGX processor is soldered into the
motherboard and requires a custom chipset, it is only sold in a complete motherboard form.
There is also an improved MMX-enhanced MediaGX processor that features MPEG1 support,
Microsoft PC97 compliance for Plug-and-Play access, integrated game port control, and AC97
audio compliance. It supports Windows 95 and DOS-based games, and MMX software as well.
Such systems will also include two universal serial bus (USB) ports, which will accommodate the
new generation of USB peripherals such as printers, scanners, joysticks, cameras, and more.
The MediaGX processor is offered at 166 and 180MHz, while the MMX-enhanced MediaGX
processor is available at 200MHz and 233 MHz. Compaq is using the MMX-enhanced MediaGX
processor in its Presario 1220 notebook PCs, which is a major contract win for Cyrix. Other retailers and resellers are offering low-end, low-cost systems in retail stores nationwide.
Cyrix/IBM 6x86 (M1) and 6x86MX (MII)
The Cyrix 6x86 processor family consists of the now-discontinued 6x86 and the newer 6x86MX
processors. They are similar to the AMD-K5 and K6 in that they offer sixth-generation internal
designs in a fifth-generation P5 Pentium compatible Socket 7 exterior.
The Cyrix 6x86 and 6x86MX (renamed MII) processors incorporate two optimized superpipelined
integer units and an on-chip floating-point unit. These processors include the dynamic execution
capability that is the hallmark of a sixth-generation CPU design. This includes branch prediction
and speculative execution.
The
and
and
and
6x86MX/MII processor is compatible with MMX technology to run the latest MMX games
multimedia software. With its enhanced memory-management unit, a 64KB internal cache,
other advanced architectural features, the 6x86MX processor achieves higher performance
offers better value than competitive processors.
Features and benefits of the 6x86 processors include
■ Superscalar architecture. Two pipelines to execute multiple instructions in parallel.
■ Branch prediction. Predicts with high accuracy the next instructions needed.
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■ Speculative execution. Allows the pipelines to continuously execute instructions following a
branch without stalling the pipelines.
■ Out-of-order completion. Lets the faster instruction exit the pipeline out of order, saving processing time without disrupting program flow.
The 6x86 incorporates two caches: a 16KB dual-ported unified cache and a 256-byte instruction
line cache. The unified cache is supplemented with a small quarter-K sized high-speed, fully associative instruction line cache. The improved 6x86MX design quadruples the internal cache size to
64KB, which significantly improves performance.
The 6x86MX also includes the 57 MMX instructions that speed up the processing of certain computing-intensive loops found in multimedia and communication applications.
All 6x86 processors feature support for System Management Mode (SMM). This provides an interrupt that can be used for system power management or software transparent emulation of I/O
peripherals. Additionally, the 6x86 supports a hardware interface that allows the CPU to be
placed into a low-power suspend mode.
The 6x86 is compatible with x86 software and all popular x86 operating systems, including
Windows 95/98, Windows NT, OS/2, DOS, Solaris, and UNIX. Additionally, the 6x86 processor
has been certified Windows 95 compatible by Microsoft.
As with the AMD-K6, there are some unique motherboard requirements for the 6x86 processors.
Cyrix maintains a list of recommended motherboards on their Web site that should be consulted
if you are considering installing one of these chips in a board.
When installing or configuring a system with the 6x86 processors, you have to set the correct
motherboard bus speed and multiplier settings. The Cyrix processors are numbered based on a Prating scale, which is not the same as the true megahertz clock speed of the processor.
See “Cyrix P-Ratings” earlier in this chapter to see the correct and true speed settings for the
Cyrix 6x86 processors.
Note that because of the use of the P-rating system, the actual speed of the chip is not the same
number at which it is advertised. For example, the 6x86MX-PR300 is not a 300MHz chip; it actually runs at only 263MHz or 266MHz, depending on exactly how the motherboard bus speed and
CPU clock multipliers are set. Cyrix says it runs as fast as a 300MHz Pentium, hence the P-rating.
Personally, I wish they would label the chips at the correct speed, and then say that it runs faster
than a Pentium at the same speed.
To install the 6x86 processors in a motherboard, you also have to set the correct voltage.
Normally, the markings on top of the chip indicate which voltage setting is appropriate. Various
versions of the 6x86 run at 3.52v (use VRE setting), 3.3v (VR setting), or 2.8v (MMX) settings.
The MMX versions use the standard split-plane 2.8v core 3.3v I/O settings.
P7 (786) Seventh-Generation Processors
What is coming after the Pentium III? The next processor is code-named either P7 or Merced.
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Intel has indicated that the new 64-bit Merced processor will be available in sample volumes in
1999, with planned production volumes moving from 1999 to mid-2000. The Merced processor
will be the first processor in Intel’s IA-64 (Intel Architecture 64-bit) product family, and will incorporate innovative performance-enhancing architecture techniques, such as predication and speculation.
Merced
The most current generation of processor is the P6, which was first seen in the Pentium Pro introduced in November of 1995, and most recently found in the latest Pentium III processors.
Obviously, then, the next generation processor from Intel will be called the P7.
Although the Merced processor program is still far from being released, the program has made
considerable progress to date according to Intel, including
■ Definition of the 64-bit instruction set architecture with Hewlett-Packard
■ Completion of the fundamental microarchitecture design
■ Completion of functional model and initial physical layout
■ Completion of mechanical and thermal design and validation with system vendors
■ Specifications complete and designs underway for chipset and other system components
■ Progress on 64-bit compiler development and IA-64 software development kits
■ Real-time software emulation capability to speed the development of IA-64 optimized software
■ Multiple operating systems running in Merced simulation environment
■ All required platform components planned for alignment with 1999 Merced processor samples for initial system assembly and testing
Intel’s IA-64 product family is expected to expand the capabilities of the Intel architecture to
address the high-performance server and workstation market segments. A variety of industry
players—among them leading workstation and server-system manufacturers, leading operating
system vendors, and dozens of independent software vendors—have already publicly committed
their support for the Merced processor and the IA-64 product family.
As with previous new processor introductions, the P7 will not replace the P6 or P5, at least not at
first. It will feature an all new design that will be initially expensive and found only in the highest end systems such as file servers or workstations. Intel expects the P7 will become the mainstream processor by the year 2004 and that the P6 will likely be found in low-end systems only.
Intel is already developing an even more advanced P7 processor, due to ship in 2001, which will
be significantly faster than Merced.
Intel and Hewlett-Packard began jointly working on the P7 processor in 1994. It was then that
they began a collaboration on what will eventually become Intel’s next-generation CPU.
Although we don’t know exactly what the new CPU will be like, Intel has begun slowly releasing
information about the new processor to prepare the industry for its eventual release. In October
of 1997, more than three years after they first disclosed their plan to work together on a new
microprocessor architecture, Intel and HP officially announced some of the new processor’s technical details.
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The first chip to implement the P7 architecture won’t ship until late 1999.
Merced will be the first microprocessor that will be based on the 64-bit, next-generation Intel
architecture-64 (IA-64) specification. IA-64 is a completely different processor design, which will
use Very Long Instruction Words (VLIW), instruction prediction, branch elimination, speculative
loading, and other advanced processes for enhancing parallelism from program code. The new
chip will feature elements of both CISC and RISC design.
There is also a new architecture Intel calls Explicitly Parallel Instruction Computing (EPIC), which
will let the processor execute parallel instructions—several instructions at the same time. In the P7,
three instructions will be encoded in one 128-bit word, so that each instruction has a few more
bits than today’s 32-bit instructions. The extra bits let the chip address more registers and tell the
processor which instructions to execute in parallel. This approach simplifies the design of processors with many parallel-execution units and should let them run at higher clock rates. In other
words, besides being capable of executing several instructions in parallel within the chip, the P7
will have the capability to be linked to other P7 chips in a parallel processing environment.
Besides having new features and running a completely new 64-bit instruction set, Intel and HP
promise full backward compatibility between the Merced, the current 32-bit Intel x86 software,
and even HP’s own PA-RISC software. The P7 will incorporate three different kinds of processors
in one and therefore be capable of running advanced IA-64 parallel processing software and IA-32
Windows and HP-RISC UNIX programs at the same time. In this way, Merced will support 64-bit
instructions while retaining compatibility with today’s 32-bit applications. This backward compatibility will be a powerful selling point.
To use the IA-64 instructions, programs will have to be recompiled for the new instruction set.
This is similar to what happened in 1985, when Intel introduced the 80386, the first 32-bit PC
processor. The 386 was to give IBM and Microsoft a platform for an advanced 32-bit operating
system that tapped this new power. To ensure immediate acceptance, the 386 and future 32-bit
processors still ran 16-bit code. To take advantage of the 32-bit capability first found in the 386,
new software would have to be written. Unfortunately, software evolves much more slowly than
hardware. It took Microsoft a full 10 years after the 386 debuted to release Windows 95, the first
mainstream 32-bit operating system for Intel processors.
Intel claims that won’t happen with the P7. Despite that, it will likely take several years before
the software market shifts to 64-bit operating systems and software. The installed base of 32-bit
processors is simply too great, and the backward compatible 32-bit mode of the P7 will allow it to
run 32-bit software very well, because it will be done in the hardware rather than through software emulation.
Merced will use 0.18 micron technology, which is one generation beyond the 0.25 micron
process used today. This will allow them to pack many more transistors in the same space. Early
predictions have the Merced sporting between 10 and 12 million transistors!
Intel’s initial goal with IA-64 is to dominate the workstation and server markets, competing with
chips such as the Digital Alpha, Sun Sparc, and Motorola PowerPC. Microsoft will provide a
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version of Windows NT that runs on the P7, and Sun plans to provide a version of Solaris, its
UNIX operating-system software, to support Merced as well. NCR has already announced that it
will build Merced-powered systems that use Solaris.
Merced will be available in a new package called the Pin Array Cartridge (PAC). This cartridge will
include cache and will plug into a socket on the motherboard and not a slot. The package is
about the size of a standard index card, weighs about 6oz (170g), and has an alloy metal on its
base to dissipate the heat. Merced has clips on its sides, allowing four to be hung from a motherboard, both below and above.
Merced will have three levels of cache. A new L0 cache will be closely tied to the execution unit.
It will be backed by on-chip L1 cache. The multimegabyte L2 cache will be housed on a separate
die but contained within the cartridge.
Merced will be followed in late 2001 by a second IA-64 processor code-named McKinley.
McKinley will have large, on-chip L2 cache and target clock speeds of more than 1GHz, offering
more than twice the performance of Merced, according to Intel reps. Following McKinley will be
Madison, based on 0.13 micron technology. Both Merced and McKinley are based on 0.18 micron
technology.
Processor Upgrades
Since the 486, processor upgrades have been relatively easy for most systems. With the 486 and
later processors, Intel designed in the capability to upgrade by designing standard sockets that
would take a variety of processors. Thus, if you have a motherboard with Socket 3, you can put
virtually any 486 processor in it; if you have a Socket 7 motherboard, it should be capable of
accepting virtually any Pentium processor.
To maximize your motherboard, you can almost always upgrade to the fastest processor your particular board will support. Normally, that can be determined by the type of socket on the motherboard. Table 3.44 lists the fastest processor upgrade solution for a given processor socket.
Table 3.44
Maximum Processor Speeds by Socket
Socket Type
Fastest Processor Supported
Socket 1
5x86–133MHz with 3.3v adapter
Socket 2
5x86–133MHz with 3.3v adapter
Socket 3
5x86–133MHz
Socket 4
Pentium OverDrive 133MHz
Socket 5
Pentium MMX 233MHz or AMD-K6 with 2.8v adapter
Socket 7
AMD-K6-2, K6-3, up to 475MHz
Socket 8
Pentium Pro OverDrive (333MHz Pentium II performance)
Slot 1
Celeron 466MHz (66MHz bus)
Slot 1
Pentium III 550MHz (100MHz bus)
Slot 2
Pentium III Xeon 550MHz (100MHz bus)
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For example, if your motherboard has a Pentium Socket 5, you can install a Pentium MMX
233MHz processor with a 2.8v voltage regulator adapter, or optionally an AMD-K6, also with a
voltage regulator adapter. If you have Socket 7, your motherboard should be capable of supporting the lower voltage Pentium MMX or AMD-K6 series directly without any adapters. The K6-2
and K6-3 are the fastest and best processors for Socket 7 motherboards.
Rather than purchasing processors and adapters separately, I normally recommend you purchase
them together in a module from companies such as Kingston or Evergreen (see the Vendor List
on the CD).
Upgrading the processor can, in some cases, double the performance of a system, such as if you
were going from a Pentium 100 to an MMX 233. However, if you already have a Pentium 233,
you already have the fastest processor that goes in that socket. In that case, you really should
look into a complete motherboard change, which would let you upgrade to a Pentium II processor at the same time. If your chassis design is not proprietary and your system uses an industry
standard Baby-AT or ATX motherboard design, I normally recommend changing the motherboard
and processor rather than trying to find an upgrade processor that will work with your existing
board.
OverDrive Processors
Intel has stated that all its future processors will have OverDrive versions available for upgrading
at a later date. Often these are repackaged versions of the standard processors, sometimes including necessary voltage regulators and fans. Usually they are more expensive than other solutions,
but they are worth a look.
OverDrive Processor Installation
You can upgrade many systems with an OverDrive processor. The most difficult aspect of the
installation is having the correct OverDrive processor for your system. Currently, 486 Pentium
OverDrive processors are available for replacing 486SX and 486DX processors. Pentium and
Pentium-MMX OverDrive processors are also available for some Pentium processors.
Unfortunately, Intel no longer offers upgrade chips for 168-pin socket boards. Table 3.45 lists the
current OverDrive processors offered by Intel.
Table 3.45
Intel OverDrive Processors
Processor Designation
Replaces
Socket
Heat Sink
486 Pentium OverDrive
486SX/DX/SX2/DX2
Socket 2 or 3
Active
120/133 Pentium
Pentium 60/66
Socket 4
Active OverDrive
200MHz Pentium OverDrive
Pentium 75/90/100
Socket 5/7
Active with MMX
Upgrades that use the newer OverDrive chips for Sockets 2–7 are likely to be much easier because
these chips almost always go into a ZIF socket and, therefore, require no tools. In most cases, special configuration pins in the socket and on the new OverDrive chips take care of any jumper settings for you. In some cases, however, you might have to set some jumpers on the motherboard
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to configure the socket for the new processor. If you have an SX system, you also will have to run
your system’s Setup program because you must inform the CMOS memory that a math coprocessor is present. (Some DX systems also require you to run the setup program.) Intel provides a utility disk that includes a test program to verify that the new chip is installed and functioning
correctly.
After verifying that the installation functions correctly, you have nothing more to do. You do not
need to reconfigure any of the software on your system for the new chip. The only difference
that you should notice is that everything works nearly twice as fast as it did before the upgrade.
OverDrive Compatibility Problems
Although you can upgrade many older 486SX or 486DX systems with the OverDrive processors,
some exceptions exist. Four factors can make an OverDrive upgrade difficult or impossible:
■ BIOS routines that use CPU-dependent timing loops
■ Lack of clearance for the OverDrive heat sink (25MHz and faster)
■ Inadequate system cooling
■ A 486 CPU that is soldered in rather than socketed
In some rare cases, problems may occur in systems that should be upgradable but are not. One of
these problems is related to the ROM BIOS. A few 486 systems have a BIOS that regulates hardware operations by using timing loops based on how long it takes the CPU to execute a series of
instructions. When the CPU suddenly is running twice as fast, the prescribed timing interval is
too short, resulting in improper system operation or even hardware lockups. Fortunately, you
usually can solve this problem by upgrading the system’s BIOS. Intel offers BIOS updates with the
OverDrive processors it sells.
Another problem is related to physical clearance. All OverDrive chips have heat sinks glued or
fastened to the top of the chip. The heat sink can add 0.25 to 1.2 inches to the top of the chip.
This extra height can interfere with other components in the system, especially in small desktop
systems and portables. Solutions to this problem must be determined on a case-by-case basis. You
can sometimes relocate an expansion card or disk drive, or even modify the chassis slightly to
increase clearance. In some cases, the interference cannot be resolved, leaving you only the
option of running the chip without the heat sink. Needless to say, removing the glued-on heat
sink will at best void the warranty provided by Intel and will at worst damage the chip or the system due to overheating. I do not recommend removing the heat sink.
The OverDrive chips can generate up to twice the heat of the chips that they replace. Even with
the active heat sink/fan built into the faster OverDrive chips, some systems do not have enough
airflow or cooling capability to keep the OverDrive chip within the prescribed safe
operating-temperature range. Small desktop systems or portables are most likely to have cooling
problems. Unfortunately, only proper testing can indicate whether a system will have a heat
problem. For this reason, Intel has been running an extensive test program to certify systems that
are properly designed to handle an OverDrive upgrade.
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Finally, some systems have a proprietary design that precludes the use of the OverDrive processor.
This would, for example, include virtually all portable, laptop, or notebook computers that have
their processor soldered into the motherboard. Some of the newer ones use the Intel Mobile
Module, which is potentially upgradable.
To clarify which systems are tested to be upgradable without problems, Intel has compiled an
extensive list of compatible systems. To determine whether a PC is upgradable with an OverDrive
processor, contact Intel via its FAXback system (see the Vendor List on the CD) and ask for the
OverDrive Processor Compatibility Data documents. The information is also available on Intel’s
Web site. These documents list the systems that have been tested with the OverDrive processors
and indicate which other changes you might have to make for the upgrade to work (for example,
a newer ROM BIOS or Setup program).
Note
If your system is not on the list, the warranty on the OverDrive processor is void. Intel recommends OverDrive
upgrades only for systems that are in the compatibility list. The list also includes notes about systems that may
require a ROM upgrade, a jumper change, or perhaps a new setup disk.
After upgrading your system, I suggest running a diagnostic program such as the Norton Utilities
to verify that the new processor is running correctly.
◊◊ See “Norton Utilities Diagnostics,” p. 1296.
Processor Benchmarks
People love to know how fast (or slow) their computers are. We have always been interested in
speed; it is human nature. To help us with this quest, various benchmark test programs can be
used to measure different aspects of processor and system performance. Although no single
numerical measurement can completely describe the performance of a complex device like a
processor or a complete PC, benchmarks can be useful tools for comparing different components
and systems.
However, the only truly accurate way to measure your system’s performance is to test the system
using the actual software applications you use. Though you think you might be testing one component of a system, often other parts of the system can have an effect. It is inaccurate to compare
systems with different processors, for example, if they also have different amounts or types of
memory, different hard disks, video cards, and so on. All these things and more will skew the test
results.
Benchmarks can normally be divided into two kinds: component or system tests. Component
benchmarks measure the performance of specific parts of a computer system, such as a processor,
hard disk, video card, or CD-ROM drive, while system benchmarks typically measure the performance of the entire computer system running a given application or test suite.
Benchmarks are, at most, only one kind of information that you can use during the upgrading or
purchasing process. You are best served by testing the system using your own set of software
operating systems and applications, and in the configuration you will be running.
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Chapter 3
There are several companies that specialize in benchmark tests and software. The following table
lists the company and the benchmarks they are known for. You can contact these companies via
the information in the Vendor List on the CD.
Company
Benchmarks
Published
Benchmark
Type
Intel
iCOMP index 2.0
Processor
Intel
iCOMP index 2.0
System Intel Media Benchmark
Business Applications
SYSmark/NT
System
Performance Corporation
(BAPCo)
Business Applications
SYSmark/NT,
SYSmark95
Performance Corporation
for Windows
(BAPCo)
System
Standard Performance
SPECint95
Evaluation Corporation
(SPEC)
Processor
Standard Performance
SPECint95,
Processor
Evaluation Corporation
SPECfp95
(SPEC)
Ziff-Davis Benchmark
CPUmark32
Processor Operation
Ziff-Davis Benchmark
Winstone 98
System Operation
Ziff-Davis Benchmark
WinBench 98
System Operation
Ziff-Davis Benchmark
CPUmark32,
Winstone 98,
WinBench 98, 3D
WinBench 98
System Operation
Symantec Corporation
Norton SI32
Processor
Symantec Corporation
Norton SI32,
System
Norton Multimedia
Benchmark
Processor Troubleshooting Techniques
Processors are normally very reliable. Most PC problems will be with other devices, but if you suspect the processor, there are some steps you can take to troubleshoot it. The easiest thing to do is
to replace the microprocessor with a known good spare. If the problem goes away, the original
processor is defective. If the problem persists, the problem is likely elsewhere.
Table 3.46 provides a general troubleshooting checklist for processor-related PC problems.
Table 3.46
Troubleshooting Processor-Related Problems
Problem
Identification
System is dead, no
cursor, no beeps, no
fan
Possible Cause
Resolution
Power cord failure
Plug in or replace power cord. Power cords can fail
even though they look fine.
Power supply Failure
Replace the power supply. Use a known-good spare
for testing.
(continues)
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Troubleshooting Processor-Related Problems
Problem
Identification
Possible Cause
Resolution
Motherboard failure
Replace motherboard. Use a known good spare for
testing.
Memory failure
Remove all memory except 1 bank and retest. If the
system still won’t boot replace bank 1.
System is dead, no
beeps, or locks up
before POST begins
All components
either not installed
or incorrectly
installed
Check all peripherals, especially memory and
graphics adapter. Reseat all boards and socketed
components.
System beeps on
startup, fan is running,
no cursor on screen.
Improperly Seated
or Failing Graphics
Adapter
Reseat or replace graphics adapter. Use known
good spare for testing.
Locks up during or
shortly after POST
Poor Heat Dissipation
Check CPU heat sink/fan; replace if necessary, use
one with higher capacity
Improper voltage
settings
Set motherboard for proper core processor voltage
Wrong motherboard
bus speed
Set motherboard for proper speed
Wrong CPU clock
multiplier
Jumper motherboard for proper clock multiplier
Old BIOS
Update BIOS from manufacturer
Board is not
configured properly
Check manual and jumper board accordingly to
proper bus and multiplier settings
Poor heat dissipation
Check CPU fan; replace if necessary, may need
higher capacity heat sink
Improper voltage
settings
Jumper motherboard for proper core voltage
Wrong motherboard
bus speed
Jumper motherboard for proper speed
Wrong CPU clock
multiplier
Jumper motherboard for proper clock multiplier
Applications will
not install or run
Improper drivers or incompatible hardware; update
drivers and check for compatibility issues
Monitor turned off or
failed
Check monitor and power to monitor. Replace with
known, good spare for testing
Improper CPU
identification
during POST
Operating system will
not boot
System appears to
work, but no video
is displayed
If during the POST the processor is not identified correctly, your motherboard settings might be
incorrect or your BIOS might need to be updated. Check that the motherboard is jumpered or
configured correctly for the processor that you have, and make sure that you have the latest BIOS
for your motherboard.
If the system seems to run erratically after it warms up, try setting the processor to a lower speed
setting. If the problem goes away, the processor might be defective or overclocked.
Many hardware problems are really software problems in disguise. Make sure you have the latest
BIOS for your motherboard, as well as the latest drivers for all your peripherals. Also it helps to
use the latest version of your given operating system since there will normally be fewer problems.
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Chapter 4
4
203 203
Motherboards and
Buses
SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE
Motherboard Form Factors
Motherboard Components
Chipsets
Intel Chipsets
Fifth-Generation (P5 Pentium Class) Chipsets
Sixth-Generation (P6 Pentium Pro/Pentium II/III Class)
Chipsets
Super I/O Chips
System Bus Functions and Features
The Need for Expansion Slots
Types of I/O Buses
System Resources
Resolving Resource Conflicts
Knowing What to Look For (Selection Criteria)
CHAPTER 4
Processor Sockets/Slots
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Motherboard Form Factors
Without a doubt, the most important component in a PC system is the main board or motherboard. Some companies refer to the motherboard as a system board or planar. The terms, motherboard, main board, system board, and planar are interchangeable. In this chapter, we will examine
the different types of motherboards available and those components usually contained on the
motherboard and motherboard interface connectors.
There are several common form factors used for PC motherboards. The form factor refers to the
physical dimensions and size of the board, and dictates what type of case the board will fit into.
Some are true standards (meaning that all boards with that form factor are interchangeable),
while others are not standardized enough to allow for true interchangeability. Unfortunately
these nonstandard form factors preclude any easy upgrade, which generally means they should
be avoided. The more commonly known PC motherboard form factors include the following:
Obsolete Form Factors
Modern Form Factors
■ Baby-AT
■ ATX
■ Full-size AT
■ Micro-ATX
■ LPX (semi-proprietary)
■ Flex-ATX
■ NLX
All Others
■ Proprietary Designs (Compaq,
Packard Bell, Hewlett-Packard,
notebook/portable systems, etc.)
■ WTX
Motherboards have evolved over the years from the original Baby-AT size and shape boards used
in the original IBM PC and XT, to the current ATX, NLX, and WTX boards used in most full-size
desktop and tower systems. ATX has a number of variants, including Micro-ATX (which is a
smaller version of the ATX form factor used in the smaller systems) to Flex-ATX (an even smaller
version for the lowest-cost home PCs). NLX is designed for corporate desktop type systems; WTX
is for workstations and medium duty servers. The following table shows the modern industrystandard form factors and their recommended uses.
Form Factor
Use
ATX
Standard desktop, mini-tower and full-tower systems, most common form factor today, most
flexible design
Micro-ATX
Lower cost desktop or mini-tower systems
Flex-ATX
Least expensive small desktop or mini-tower systems
NLX
Corporate desktop or mini-tower systems, integrated 10/100 Ethernet, easiest and quickest
to service
WTX
High performance workstations, midrange servers
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Although the Baby-AT, Full-size AT, and LPX boards were once popular, they have all but been
replaced by more modern and interchangeable form factors. The modern form factors are true
standards, which guarantees improved interchangeability within each type. This means that ATX
boards will interchange with other ATX boards, NLX with other NLX and so on. The additional
features found on these boards as compared to the obsolete form factors, combined with true
interchangeability, has made the migration to these newer form factors quick and easy. Today I
only recommend purchasing systems with one of the modern industry-standard form factors.
Anything that does not fit into one of the industry standard form factors is considered proprietary. Unless there are special circumstances, I do not recommend purchasing systems with proprietary board designs. They will be virtually impossible to upgrade and very expensive to repair
later, because the motherboard, case, and often power supply will not be interchangeable with
other models. I call proprietary form factor systems “disposable” PCs, since that’s what you must
normally do with them when they are too slow or need repair out of warranty.
The following sections detail each of the standard form factors.
Baby-AT
The first popular PC motherboard was, of course, the original IBM PC released in 1981. Figure 4.1
shows how this board looked. IBM followed the PC with the XT motherboard in 1983, which had
the same basic shape as the PC board, but had eight slots instead of five. Also, the slots were
spaced 0.8 inch apart instead of 1 inch apart as in the PC (see Figure 4.2). The XT also eliminated
the weird cassette port in the back, which was supposed to be used to save BASIC programs on
cassette tape instead of the much more expensive (at the time) floppy drive.
◊◊ See “An Introduction to the PC (5150),” in “IBM Personal Computer Family Hardware” on the CD
◊◊ See “An Introduction to the XT (5160),” in “IBM Personal Computer Family Hardware” on the CD
The minor differences in the slot positions and the now lonesome keyboard connector on the
back required a minor redesign of the case. This motherboard became very popular and many
other PC motherboard manufacturers of the day copied IBM’s XT design and produced similar
boards. By the time most of these clones or compatible systems came out, IBM had released their
AT system, which initially used a larger form factor motherboard. Due to the advances in circuit
miniaturization, these companies found they could fit all the additional circuits found on the 16bit AT motherboard into the XT motherboard form factor. Rather than call these boards XT-sized,
which may have made people think they were 8-bit designs, they referred to them as Baby-AT,
which ended up meaning an XT-sized board with AT motherboard design features (16-bit or
greater).
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8259 Interrupt controller
Cassette I/O
Keyboard I/O
8-bit ISA bus slots
{
J1
J2
J3
J4
J6
J5
J7
System-board
power connections
Clock chip trimmer
1
2
1
1
Intel 8087 math
coprocessor
8
8
Intel 8088 processor
Read-only memory
DIP switch block 2
8237 DMA controller
64K to 256K
read/write
memory with
parity checking
{
DIP switch block 1
P3
Pin 1
Figure 4.1
Speaker
output
P4
Cassette microphone
or auxiliary select
IBM PC motherboard (circa 1981).
Thus, the Baby-AT form factor is essentially the same as the original IBM XT motherboard. The
only difference is a slight modification in one of the screw hole positions to fit into an AT-style
case (see Figure 4.3). These motherboards also have specific placement of the keyboard and slot
connectors to match the holes in the case. Note that virtually all full-size AT and Baby-AT motherboards use the standard 5-pin DIN type connector for the keyboard. Baby-AT motherboards can
be used to replace full-sized AT motherboards and will fit into a number of different case designs.
Because of their flexibility, from 1983 into early 1996 the Baby-AT form factor was the most popular motherboard type. Starting in mid-1996, Baby-AT was replaced by the superior ATX motherboard design, which is not directly interchangeable. Most systems sold since 1996 have used the
improved ATX, micro-ATX, or NLX designs, and Baby-AT is getting harder and harder to come by.
Figure 4.3 shows the dimensions and layout of a Baby-AT motherboard.
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Clock chip trimmer
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Keyboard I/O
8-bit ISA bus slots
J1
J2
J3
J4
J5
J6
J7
J8
J9
System-board power
connections
Intel 8087 math
coprocessor
INTEL 8088
processor
ROM BASIC
ROM BIOS
8259 Interrupt
controller
System Configuration DIP
switches
8237 DMA controller
As much as
640K read/
write memory
with parity
checking
{
P3
Pin 1
Figure 4.2
Speaker output
IBM PC-XT motherboard (circa 1983).
Any case that accepts a full-sized AT motherboard will also accept a Baby-AT design. Since its
debut in the IBM XT motherboard in 1983 and lasting well into 1996, the Baby-AT motherboard
form factor was, for that time, the most popular design. You can get a PC motherboard with virtually any processor from the original 8088 to the fastest Pentium III in this design, although the
pickings are slim in the Pentium II/III category. As such, systems with Baby-AT motherboards are
virtually by definition upgradable systems. Because any Baby-AT motherboard can be replaced
with any other Baby-AT motherboard, this is an interchangeable design.
Until mid-1996 I had recommended to most people that they make sure any PC system they purchased had a Baby-AT motherboard. They would sometimes say, “I’ve never heard of that brand
before.” “Of course,” I’d tell them, “that’s not a brand, but a shape!” The point being that if they
had a Baby-AT board in their system, when a year or so goes by and they longed for something
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faster, it would be easy and inexpensive to purchase a newer board with a faster processor and
simply swap it in. If they purchased a system with a proprietary or semi-proprietary board, they
would be out of luck when it came time to upgrade, because they had a disposable PC.
Disposable PCs may be cheaper initially, but they are usually much more expensive in the long
run because they can’t easily or inexpensively be upgraded or repaired.
3.75"
.40"
.65"
6.50"
6.00"
8.35"
13.04"
.45"
.34"
5.55"
8.57"
Figure 4.3
Baby-AT motherboard form factor dimensions.
The easiest way to identify a Baby-AT form factor system without opening it is to look at the rear
of the case. In a Baby-AT motherboard, the cards plug directly into the board at a 90-degree
angle; in other words, the slots in the case for the cards are perpendicular to the motherboard.
Also, the Baby-AT motherboard has only one visible connector directly attached to the board,
which is the keyboard connector. Normally this connector is the full-sized 5-pin DIN type connector; although, some Baby-AT systems will use the smaller 6-pin min-DIN connector (sometimes called a PS/2 type connector) and may even have a mouse connector. All other connectors
will be mounted on the case or on card edge brackets and attached to the motherboard via
cables.
Figure 4.4 shows the connector profile at the rear of Baby-AT boards. The keyboard connector is
visible through an appropriately placed hole in the case.
◊◊ See “Keyboard/Mouse Interface Connectors,” p. 920.
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5-Pin
DIN Connector
1
3
4
5
2
Motherboard
Figure 4.4
The Baby-AT motherboard rear connector profile showing keyboard connector position.
Baby-AT boards all conform to specific width, screw hole, slot, and keyboard connector locations,
but one thing that can vary is the length of the board. Versions have been built that are shorter
than the full 13-inch length; these are often called Mini-AT, Micro-AT, or even things such as 2/3Baby or 1/2-Baby. Even though they may not have the full length, they still bolt directly into the
same case as a standard Baby-AT board, and can be used as a direct replacement for one.
Full-Size AT
The full-size AT motherboard matches the original IBM AT motherboard design. This allows for a
very large board of up to 12 inches wide by 13.8 inches deep. When the full-size AT board
debuted in 1984, IBM needed more room for additional circuits when they migrated from the 8bit architecture of the PC/XT to the 16-bit architecture of the AT. So, IBM started with an XT
board and extended it in two directions (see Figure 4.5).
The board was redesigned to make it slightly smaller a little over a year after being introduced.
Then it was redesigned again as IBM shrank it down to XT-size in a system they called the XT-286
(see Figure 28.14 in Chapter 28). The XT-286 board size was virtually identical to the original XT,
and was adopted by most PC-compatible manufacturers when it became known as Baby-AT.
◊◊ See “An Introduction to the AT,” in “IBM Personal Computer Family Hardware” on the CD
◊◊ See “An Introduction to the XT Model 286,” in “IBM Personal Computer Family Hardware” on the CD
The keyboard connector and slot connectors in the full-sized AT boards still conformed to the
same specific placement requirements to fit the holes in the XT cases already in use, but a larger
case was still required to fit the larger board. Due to the larger size of the board, a full-size AT
motherboard will fit into full-size AT desktop or Tower cases only. Because these motherboards
will not fit into the smaller Baby-AT or Mini-Tower cases, and because of advances in component
miniaturization, they are no longer being produced by most motherboard manufacturers, except
in some cases for dual processor server applications.
Note that you can always replace a full-size AT motherboard with a Baby-AT board, but the opposite is not true unless the case is large enough to accommodate the full-size AT design.
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Keyboard connector
Battery connector
Math coprocessor connector
8/16-bit ISA bus slots
CMOS RAM/RTC
Display switch
8042 keyboard
controller
8259 interrupt
controllers
286 processor
Clock crystal
ROM
BIOS
sockets
8237 DMA
controllers
Variable capacitor
clock trimmer
Keylock connector
128K
Memory modules
Speaker connector
Figure 4.5
IBM AT motherboard (circa 1984).
LPX
The LPX and Mini-LPX form factor boards are a semi-proprietary design originally developed by
Western Digital in 1987 for some of their motherboards. The LP in LPX stands for Low Profile,
which is so named because these boards incorporated slots that were parallel to the main board,
allowing the expansion cards to install sideways. This allowed for a slim or low profile case
design and overall a smaller system than the Baby-AT.
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Although Western Digital no longer produces PC motherboards, the form factor lives on and has
been duplicated by many other motherboard manufacturers. Unfortunately, because the specifications were never laid out in exact detail—especially with regard to the bus riser card portion of
the design—these boards are termed semi-proprietary and are not interchangeable between manufacturers. This means that if you have a system with an LPX board, in most cases you will not
be able to replace the motherboard with a different LPX board later. You essentially have a system
that you cannot upgrade or repair by replacing the motherboard with something better. In other
words, you have what I call a disposable PC, something I would not normally recommend that
anybody purchase.
Most people are not aware of the semi-proprietary nature of the design of these boards, and they
have been extremely popular in what I call “retail store” PCs from the late ‘80s through the late
‘90s. This would include primarily Compaq and Packard Bell systems, as well as any others who
used this form factor. These boards wer most often used in Low Profile or Slimline case systems,
but can also be found in Tower cases, too. These are often lower cost systems such as those sold
at retail electronics superstores. Due to their proprietary nature, I recommend staying away from
any system that uses an LPX motherboard.
LPX boards are characterized by several distinctive features (see Figure 4.6). The most noticeable
is that the expansion slots are mounted on a bus riser card that plugs into the motherboard.
Expansion cards must plug sideways into the riser card. This sideways placement allows for the
low profile case design. Slots will be located on one or both sides of the riser card depending on
the system and case design.
Adapter cards installed in riser
Riser
card
slot
LPX
motherboard
Power supply
Floppy
LPX
motherboard
Riser
card
Drives
Memory
SIMMs
Figure 4.6
Video L2
RAM cache
Processor
socket
Typical LPX system chassis and motherboard.
Another distinguishing feature of the LPX design is the standard placement of connectors on the
back of the board. An LPX board will have a row of connectors for video (VGA 15-pin), parallel
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(25-pin), two serial ports (9-pin each), and mini-DIN PS/2 style mouse and keyboard connectors.
All these connectors are mounted across the rear of the motherboard and protrude through a slot
in the case. Some LPX motherboards may have additional connectors for other internal ports
such as Network or SCSI adapters. Figure 4.7 shows the standard form factors for the LPX and
Mini-LPX motherboards used in many systems today.
13.0
11.375
5.875
0.375
0.219
0.0
0.0
9.0
0.35
3.906
7.500
8.8125
Figure 4.7
LPX motherboard dimensions.
I am often asked, “How can I tell if a system has an LPX board before I purchase it?” Fortunately,
this is easy, and you don’t even have to open the system up or remove the cover. LPX motherboards have a very distinctive design with the bus slots on a riser card that plugs into the motherboard. This means that any card slots will be parallel to the motherboard, because the cards
stick out sideways from the riser. Looking at the back of a system, you should be able to tell
whether the card slots are parallel to the motherboard. This implies a bus riser card is used, which
also normally implies that the system is an LPX design.
The use of a riser card no longer directly implies that the motherboard is an LPX design. More
recently, a newer form factor called NLX has been released which also uses a riser card.
On an LPX board, the riser is placed in the middle of the motherboard while NLX boards have
the riser to the side (the motherboard actually plugs into the riser in NLX).
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Because the riser card is no longer used only on LPX boards, perhaps the easiest feature to distinguish is the single height row of connectors along the bottom of the board. The NLX boards have
a different connector area with both single-row and double-row connector areas.
See the section on NLX motherboards later in this chapter for more information on NLX.
See Figure 4.8 for an example of the connectors on the back of an LPX board. There are two connector arrangements shown, for systems without or with USB ports. Note that not all LPX boards
will have the built-in audio, so those connectors might be missing. Other ports can be missing
from what is shown in these diagrams, depending on exactly what options are included on a specific board.
Line
Out
PS/2
Keyboard
Mic In
Line
Out
Figure 4.8
Serial Port 2
Parallel Port
Video
Serial Port 1
USB 1 USB 2
Parallel Port
Video
PS/2
Mouse
PS/2
Keyboard
Mic In
Serial Port 1
PS/2
Mouse
LPX motherboard back panel connectors.
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The connectors along the rear of the board prevent expansion cards from being plugged directly
into the motherboard, which accounts for why riser cards are used for adding expansion boards.
While the built-in connectors on the LPX boards were a good idea, unfortunately, the LPX design
was proprietary (not a fully interchangeable standard) and thus, not a good choice. Newer motherboard form factors such as ATX, Micro-ATX, and NLX have both built-in connectors and use a
standard board design. In fact, the NLX form factor was developed as a modern replacement for
LPX.
ATX
The ATX form factor was the first of a dramatic evolution in motherboard form factors. ATX is a
combination of the best features of the Baby-AT and LPX motherboard designs, with many new
enhancements and features thrown in. The ATX form factor is essentially a Baby-AT motherboard
turned sideways in the chassis, along with a modified power supply location and connector. The
most important thing to know initially about the ATX form factor is that it is physically incompatible with either the previous Baby-AT or LPX designs. In other words, a different case and
power supply are required to match the ATX motherboard. These new case and power supply
designs have become common, and can be found in many new systems.
The official ATX specification was initially released by Intel in July 1995 and was written as an
open specification for the industry. ATX boards didn’t hit the market in force until mid-1996
when they rapidly began replacing Baby-AT boards in new systems. The ATX specification was
updated to version 2.01 in February 1997. The latest revision is ATX version 2.03, released in
December 1998. Intel has published detailed specifications so other manufacturers can use the
ATX design in their systems. Currently, ATX is the most popular motherboard form factor for
new systems, and it is the one I recommend most people get in their systems today. An ATX system will be upgradable for many years to come, exactly like Baby-AT was in the past.
ATX improves on the Baby-AT and LPX motherboard designs in several major areas:
■ Built-in double high external I/O connector panel. The rear portion of the motherboard
includes a stacked I/O connector area that is 6 1/4-inches wide by 1 3/4-inches tall. This
allows external connectors to be located directly on the board and negates the need for
cables running from internal connectors to the back of the case as with Baby-AT designs.
■ Single keyed internal power supply connector. This is a boon for the average end user who
always had to worry about interchanging the Baby-AT power supply connectors and subsequently blowing the motherboard! The ATX specification includes a single keyed and
shrouded power connector that is easy to plug in, and which cannot be installed incorrectly. This connector also features pins for supplying 3.3v to the motherboard, which
means that ATX motherboards will not require built-in voltage regulators that are susceptible to failure.
◊◊ See “Power Supply Connectors,” p. 1102.
■ Relocated CPU and memory. The CPU and memory modules are relocated so they cannot
interfere with any bus expansion cards, and they can easily be accessed for upgrade without
removing any of the installed bus adapters. The CPU and memory are relocated next to the
power supply, which is where the primary system fan is located. The improved airflow
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concentrated over the processor often eliminates the need for extra-cost and sometimes
failure-prone CPU cooling fans. There is room for a large passive heat sink on the CPU with
more than adequate clearance provided in that area.
Note
Note that systems from smaller vendors might still include CPU fans even in ATX systems, as Intel supplies processors with attached high-quality (ball bearing) fans for CPUs sold to smaller vendors. These are so-called “boxed”
processors because they are sold in single-unit box quantities instead of pallets of 100 or more like the raw CPUs
sold to the larger vendors. Intel includes the fan as insurance because most smaller vendors and system assemblers
lack the engineering knowledge necessary to perform thermal analysis, temperature measurements, and the testing
required to select the properly sized passive heat sink. By putting a fan on these “boxed” processors, Intel is covering their bases, as the fan will ensure adequate CPU cooling. This allows them to put a warranty on the boxed
processors that is independent of the system warranty. Larger vendors have the engineering talent to select the
proper passive heat sink, thus reducing the cost of the system as well as increasing reliability. With an OEM nonboxed processor, the warranty is with the system vendor and not Intel directly. Intel normally includes heat sink
mounting instructions with their motherboards if non-boxed processors are used.
■ Relocated internal I/O connectors. The internal I/O connectors for the floppy and hard disk
drives are relocated to be near the drive bays and out from under the expansion board slot
and drive bay areas. This means that internal cables to the drives can be much shorter, and
accessing the connectors will not require card or drive removal.
■ Improved cooling. The CPU and main memory are positioned so they can be cooled directly
by the power supply fan, eliminating the need for separate case or CPU cooling fans. Note
that the ATX specification originally specified that the ATX power supply fan blows into
the system chassis instead of outward. This reverse flow, or positive pressure design, pressurizes the case, which greatly minimizes dust and dirt intrusion. With the positive pressurized reverse flow design, an air filter can be easily added to the air intake vents on the
power supply, creating a system that is even more immune to dirt and dust. More recently,
the ATX specification was revised to allow the more normal standard flow, which negatively pressurizes the case by having the fan blow outward. Because the specification technically allows either type of airflow, and because some overall cooling efficiency is lost with
the reverse flow design, most power supply manufacturers provide ATX power supplies
with standard airflow fans that exhaust air from the system, otherwise called a negative
pressure design.
■ Lower cost to manufacture. The ATX specification eliminates the need for the rat’s nest of
cables to external port connectors found on Baby-AT motherboards, additional CPU or
chassis cooling fans, or onboard 3.3v voltage regulators. Instead, ATX uses a single power
supply connector and allows for shorter internal drive cables. These all conspire to greatly
reduce the cost of the motherboard the cost of a complete system—including the case and
power supply.
Figure 4.9 shows the new ATX system layout and chassis features, as you would see them looking
in with the lid off on a desktop, or sideways in a tower with the side panel removed. Notice how
virtually the entire motherboard is clear of the drive bays, and how the devices such as CPU,
memory, and internal drive connectors are easy to access and do not interfere with the bus slots.
Also notice the power supply orientation and the single power supply fan that blows into the
case directly over the high heat, cooling items such as the CPU and memory.
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Double high
expandable I/O
Single
chassis fan
Power
Supply
Processor
CPU located
near PSU
Full
length slots
Single power
connector
3 1/2"
Bay
Floppy/IDE
connectors close
to peripheral bays
Figure 4.9
5 1/4"
Bay
Easy to access
SIMM memory
ATX system chassis layout and features.
The ATX motherboard is basically a Baby-AT design rotated sideways. The expansion slots are
now parallel to the shorter side dimension and do not interfere with the CPU, memory, or I/O
connector sockets. There are actually two basic sizes of ATX boards. In addition to a full-sized
ATX layout, Intel also has specified a mini-ATX design, which is a fully compatible subset in size
and will fit into the same case. A full size ATX board is 12” wide × 9.6” deep (305mm × 244mm).
The mini-ATX board is 11.2” × 8.2” (284mm × 208mm).
Although the case holes are similar to the Baby-AT case, cases for the two formats are generally
not compatible. The power supplies would require a connector adapter to be interchangeable, but
the basic ATX power supply design is similar to the standard Slimline power supply. The ATX and
mini-ATX motherboard dimensions are shown in Figure 4.10.Clearly, the advantages of the ATX
form factor make it the best choice for new systems. For backward compatibility, you can still
find Baby-AT boards for use in upgrading older systems, but the choices are becoming slimmer
every day. I would never recommend building or purchasing a new system with a Baby-AT motherboard, as you will severely limit your future upgrade possibilities. In fact, I have been recommending only ATX systems for new system purchases since late 1996 and will probably continue
to do so for the next several years.
The best way to tell whether your system has an ATX-board design without removing the lid is to
look at the back of the system. There are two distinguishing features that identify ATX. One is
that the expansion boards plug directly into the motherboard. There is no riser card like with
LPX or NLX and so the slots will be perpendicular to the plane of the motherboard. Also, ATX
boards have a unique double-high connector area for all the built-in connectors on the motherboard (see Figure 4.11). This will be found just to the side of the bus slot area, and can be used to
easily identify an ATX board.
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Chapter 4
5.196
.812
PIN I ISA TO
PIN I PCI
SHARED SLOT
.800 TYP.
BETWEEN
CONNECTORS
Datum 0,0
.500
6.250
REAR 1/10 WINDOW IN CHASSIS
.400
.600
.900
1.225
ACCESSIBLE CONNECTOR 1/0 AREA
ISA CONNECTOR
(4 PLACES)
6. 00
8.950
PCI CONNECTOR
(4 PLACES)
7.550
(MINI ATX)
9.600
M
M
M
5X Ø .156
MINI ATX
MOUNTING HOLES
MARKED (M)
M
10X Ø .156
MTG HOLES
MINI ATX BOARD
11.2" x 8.2"
3.100
4.900
10.300 (MINI ATX)
.650
11.100
12.000
Figure 4.10
ATX specification version 2.03, showing ATX and mini-ATX dimensions.
The specification and related information about the ATX, mini-ATX, micro-ATX, flex-ATX, or
NLX form factor specifications are available from the Platform Development Support Web site at
http://www.teleport.com/~ffsupprt/. This single public site replaces the previous independent
sites dedicated to those form factors. The Platform Developer site provides form factor specifications and design guides, as well as design considerations for new technologies, information on
initiative supporters, vendor products through a “One-Stop-Shopping” mall link, and a form factor bulletin board.
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A
F
H
C
B
Figure 4.11
D
E
G
I
J
K
A
PS/2 keyboard or mouse
G
Serial Port B
B
PS/2 keyboard or mouse
H
MIDI/game Port (optional)
C
USB Port 1
I
Audio Line Out (optional)
D
USB Port 0
J
Audio Line In (optional)
E
Serial Port A
K
Audio Mic In (optional)
F
Parallel Port
Typical ATX motherboard rear panel connectors.
Micro-ATX
Micro-ATX is a motherboard form factor originally introduced by Intel in December of 1997 as an
evolution of the ATX form factor for smaller and lower cost systems. The reduced size as compared to standard ATX allows for a smaller chassis, motherboard, and power supply, reducing the
cost of entire system. The micro-ATX form factor is also backward compatible with the ATX form
factor and can be used in full-size ATX cases. During early 1999 this form factor began to really
catch on in the low-cost, sub-$1,000 PC market.
The main differences between micro-ATX and standard or mini-ATX are as follows:
■ Reduced width motherboard (9.6” [244mm] instead of 12” [305mm] or 11.2” [284mm])
■ Fewer I/O bus expansion slots
■ Smaller power supply (SFX form factor)
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The micro-ATX motherboard maximum size is only 9.6” × 9.6” (244 × 244 mm) as compared to
the full-size ATX size of 12” × 9.6” (305 × 244 mm) or the mini-ATX size of 11.2” × 8.2” (284mm
× 208mm). Even smaller boards can be designed as long as they conform to the location of the
mounting holes, connector positions, etc. as defined by the standard. Fewer slots aren’t a problem because more components such as sound and video are likely to be integrated on the motherboard and therefore won’t require separate slots. This higher integration reduces motherboard
and system costs. External buses such as USB, 10/100 Ethernet, and optionally 1394 (FireWire)
will provide additional expansion out of the box.
The specifications for micro-ATX motherboard dimensions are shown in Figure 4.12.
2.000
(53.24)
.812
(20.62)
PIN 1 IRA TO
PIN 1 PCI
SHARED SLOT
1.200
(38.48)
.80B TYP.
(20, 32)
BETWEEN CONNECTORS
.408
(10.13)
1.223
(31.12)
2.232
(54.7)
0.250
(158.73)
BEAR ISO WINDOW IN CHASSIS
ACCESSIBLE CONNECTOR ISO AREA
Dates B I D
.80B TYP.
(20, 32) BETWEEN
CONNECTORS
.408
(15.24)
.908
(22.08)
.48D
(IT.51)
PIN 1 PCI TO
PIN 1 ABP
IRA CONNECTOR
(2 PLACES)
4.100
(154.14)
8.930
(221.333)
REP CONNECTOR
9.500
(249.84)
PCI CONNECTOR
(2 PLACES)
100.150
(3.86)
MTG HOLES
.301
(20.32)
1.300
(34.28)
1.608
(43.32)
8.980
(203.2)
8.600
(243.84)
Figure 4.12
Micro-ATX specification 1.0 motherboard dimensions.
A new, small form factor (called SFX) power supply has been defined for use with micro-ATX systems. The smaller size of this power supply encourages flexibility in choosing mounting locations
within the chassis, and will allow for smaller systems which consume less power overall.
◊◊ See “SFX Style (micro-ATX Motherboards),” p. 1099.
The micro-ATX form factor is similar to ATX for compatibility. The similarities include the
following:
■ Standard ATX 20-pin power connector
■ Standard ATX I/O panel
■ Mounting holes are a subset of ATX
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These similarities will ensure that a micro-ATX motherboard will easily work in a standard ATX
chassis with a standard ATX power supply, as well as the smaller micro-ATX chassis and SFX
power supply.
The overall system size for a micro-ATX is very small. A typical case will be only 12” to 14” tall,
about 7” wide, and 12” deep. This results in a kind of micro-tower or desktop size. A typical
micro-ATX tower is shown in Figure 4.13.
Not to scale
Memory slots
9.6" (244 mm)
Processor
Alternate power
supply location
5.25" drive bay
3.5" drive bay floppy
ATX-compatible
double-high
expandable I/O window
6.25" (158.75 mm) x
1.75" (44.45 mm)
P
O
W
E
R
IDE, FDD,
front panel
connectors
Hard drive
bay
9.6"
(244 mm)
Power supply and
fan over processor
FRONT
of board
Expansion slots
Figure 4.13
9.6" x 9.6" (244 x 244 mm) motherboard
Micro-ATX system side view showing typical internal layout.
As with ATX, micro-ATX was released to the public domain by Intel so as to facilitate adoption as
a de facto standard. The specification and related information on micro-ATX are available
through the Platform Developer Web site (http://www.teleport.com/~ffsupprt/).
Flex-ATX
In March of 1999, Intel released the flex-ATX addendum to the micro-ATX specification. This
added a new and even smaller variation of the ATX form factor to the motherboard scene. FlexATX is smaller design intended to allow a variety of new PC designs, especially extremely inexpensive, smaller, consumer-oriented, appliance type systems.
Flex-ATX defines a board that is only 9.0” × 7.5” (229mm × 191mm) in size, which is the smallest of the ATX family boards. Besides the smaller size, the other biggest difference between the
flex-ATX form factor and the micro-ATX is that flex-ATX will only support socketed processors.
This means that a flex-ATX board will not have a Slot 1 or Slot 2 type connector for the cartridge
versions of the Pentium II/III processors. However, it can have Socket 7 or the newer Socket 370,
which supports up through the AMD K6-3 and Intel Celeron (Pentium II/III class) processors.
Future versions of the Pentium III will most likely become available in the Socket 370 design and
will be usable in flex-ATX boards.
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Besides the smaller size and socketed-processor only requirement, the rest of flex-ATX is backward
compatible with standard ATX, using a subset of the mounting holes and the same I/O and
power supply connector specifications (see Figure 4.14).
12.000
(304, 80)
9.600
(243, 84)
9.000
(228, 60) Back of Board
B
A
6.250" (158, 75)
wide I/O shield
C
F
FlexATX
7.500
(190, 50)
S
J
H
MicroATX
K
9.600
(243, 84)
R
G
ATX
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Front of Board
Key - Mounting Holes
FlexATX
ATZ and/or microATX
Form factor
Mounting hole locations
• FlexATX
B, C, F, H, J, S
Notes
• microATX
B, C, F, H, J, L, M, R, S
Holes R and S were added for microATX
form factor. Hole B was defined in
Full AT format.
• ATX
A, C, F, G, H, J, K, L, M
Hole F must be implemented in all
ATX 2.03-compliant chassis assemblies.
The hole was optional in the ATX 1.1
specification.
Figure 4.14 Size and mounting hole comparison between ATX, micro-ATX, and flex-ATX
motherboards.
Most flex-ATX systems will likely use the SFX (small form factor) type power supplies (introduced
in the micro-ATX specification), although if the case allows, a standard ATX power supply can
also be used.
With the addition of flex-ATX, the family of ATX boards has now grown to include four definitions of size, as shown in Table 4.1:
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ATX Motherboard Form Factors
Form Factor
Max. Width
Max. Depth
ATX
12.0” (305mm)
9.6” (244mm)
Mini-ATX
11.2” (284mm)
8.2” (208mm)
Micro-ATX
9.6” (244mm)
9.6” (244mm)
Flex-ATX
9.0” (229mm)
7.5” (191mm)
Note that these dimensions are the maximum the board can be. It is always possible to make a
board smaller as long as it conforms to the mounting hole and connector placement requirements detailed in the respective specifications. Each of these have the same basic screw hole and
connector placement requirements, so if you have a case that will fit a full-sized ATX board, you
could also mount a mini-, micro-, or flex-ATX board in that same case. Obviously if you have a
smaller case designed for micro-ATX or flex-ATX, it will not be possible to put the larger miniATX or full sized ATX boards in that case.
NLX
NLX is a new low-profile form factor designed to replace the non-standard LPX design used in
previous low-profile systems. First introduced in November of 1996 by Intel, NLX is proving to be
the form factor of choice for Slimline corporate desktop systems now and in the future. NLX is
similar in initial appearance to LPX, but with numerous improvements designed to allow full
integration of the latest technologies. NLX is basically an improved version of the proprietary
LPX design, and it is fully standardized, which means you should be able to replace one NLX
board with another from a different manufacturer—something that was not possible with LPX.
Another limitation of LPX boards is the difficulty in handling the physical size of the newer
Pentium II/III processors and their higher output thermal characteristics as well as newer bus
structures such as AGP for video. The NLX form factor has been designed specifically to address
these problems (see Figure 4.15).
Figure 4.15
NLX motherboard and riser combination.
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223
The main characteristic of an NLX system is that the motherboard plugs into the riser, unlike
LPX where the riser plugs into the motherboard. This means the motherboard can be removed
from the system without disturbing the riser or any of the expansion cards plugged into it. In
addition, the motherboard in an NLX system literally has no internal cables or connectors
attached to it! All devices that normally plug into the motherboard, such as drive cables, the
power supply, front panel light and switch connectors, etc., all plug into the riser instead (see
Figure 4.16). By using the riser card as a connector concentration point, it is possible to remove
the lid on an NLX system and literally slide the motherboard out the left side of the system without unplugging a single cable or connector on the inside. This allows for unbelievably quick
motherboard changes; in fact, I have swapped motherboards in less than 30 seconds on NLX
systems!
– (/) <
– (/) <
standard right angle
header
Floppy
IDE
IDE
– () –
Riser
Card
Figure 4.16
– () –
SIDE
sleep
reset
left speaker
FC speaker
VIEW VWO Front panel I/O
header
MOTHERBOARD
Power switch
Power LED
HD LED
Ian
Front panel I/O cable
A
female suppression
components
Case
Front
USB
Front panel I/O
EMI shield
Orientation of the riser card in an NLX system.
In addition to being able to remove the motherboard so easily, you can also remove a power supply or any disk drive without removing any other boards from the system. Such a design is a
boon for the corporate market, where ease and swiftness of servicing is a major feature. Not only
can components be replaced with lightening speed, but because of the industry standard design,
motherboards, power supplies, and other components will be interchangeable even among different systems.
Specific advantages of the NLX form factor include
■ Support for all desktop system processor technologies. This is especially important in Pentium
II/III systems, because the size of the Single Edge Contact cartridge this processor uses can
run into physical fit problems on existing Baby-AT and LPX motherboards.
■ Flexibility in the face of rapidly changing processor technologies. Backplane-like flexibility has
been built into the form by allowing a new motherboard to be easily and quickly installed
without tearing your entire system to pieces. But unlike traditional backplane systems,
many industry leaders are putting their support behind NLX.
■ Support for newer technologies. This includes Accelerated Graphics Port (AGP) high-performance graphic solutions, Universal Serial Bus (USB), and memory modules in DIMM or
RIMM form.
■ Ease and speed of servicing and repair. Compared to other industry standard interchangeable
form factors, NLX systems are by far the easiest to work on, and allow component swaps or
other servicing in the shortest amount of time.
Furthermore, with the importance of multimedia applications, connectivity support for such
things as video playback, enhanced graphics, and extended audio have been built into the motherboard. This should represent a good cost savings over expensive daughterboard arrangements
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that have been necessary for many advanced multimedia uses in the past. Although ATX also has
this support, LPX and Baby-AT don’t have the room for these additional connectors.
Figure 4.17 shows the basic NLX system layout, while the NLX motherboard dimensions are
shown in Figure 4.18. Notice that, like ATX, the system is clear of the drive bays and other chassis-mounted components. Also, the motherboard and I/O cards (which, like the LPX form factor,
are mounted parallel to the motherboard) can easily be slid in and out of the side of the chassis,
leaving the riser card and other cards in place. The processor can be easily accessed and enjoys
greater cooling than in a more closed-in layout.
Vents
Fan
Power
Supply
Vents
A.G.P.
Slot
Memory
Slots
Add-in Cards
Vents
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Vents
Riser Card
Periperals
Processor
Figure 4.17
Vents
NLX system chassis layout and cooling airflow.
The NLX motherboard is specified in three different lengths front to back of 13.6”, 11.2” or 10”
total (see Figure 4.18). With proper bracketry, the shorter boards can go into a case designed for a
longer board.
As with most of the different form factors, you can identify NLX via the unique I/O shield or
connector area at the back of the board (see Figure 4.19). I only need a quick look at the rear of
any given system to determine what type of board is contained within. The following figure
shows the unique stepped design of the NLX I/O connector area. This allows for a row of connectors all along the bottom, and has room for double-stacked connectors on one side.
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5, 08 REF
(.200)
340, 33
(13.400)
158,12 REF
(6.225)
4X 4.01
(.300)
Required Keepout Area “A”
Chapter 4
225
345, 44
(13.600)
4X
3.00
(.156)
Mounting Holes
30, 48 REF
(1.200)
223, 50
(5.100)
Maximum
Board Width
31, 36 REF
(3.400)
213, 20
(4.000)
Minimum
Board Width
198, 12
(7.800)
PRIMARY SIDE
111, 76
(4.400)
Card edge gold fingers (shown for orientation)
Figure 4.18 NLX form factor. This shows a 13.6-inch long NLX board. The NLX specification also
allows shorter 11.2-inch and 10-inch versions.
Figure 4.19
NLX motherboard I/O shield and connector area as seen from behind.
As you can see, the NLX form factor has been designed for maximum flexibility and space efficiency. Even extremely long I/O cards will fit easily, without getting in the way of other system
components—a problem with Baby-AT form factor systems.
The specification and related information about the NLX form factor are available through the
Platform Developer Web site located at http://www.teleport.com/~ffsupport/.
ATX, mini-ATX, micro-ATX, flex-ATX, and NLX form factors will be the predominant form factors used in virtually all future systems. Since these are well-defined standards that have achieved
acceptance in the marketplace, I would avoid the older, obsolete standards such as Baby-AT. I recommend avoiding LPX or other proprietary systems if upgradability is a factor because it is not
only difficult to locate a new motherboard that will fit, but LPX systems are also limited in
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expansion slots and drive bays. Overall ATX is still the best choice for most new systems where
expandability, upgradability, low cost, and ease of service are of prime importance.
WTX
WTX is a new board and system form factor developed for the mid-range workstation market.
WTX goes beyond ATX and defines the size and shape of the board and the interface between the
board and chassis, as well as required chassis features.
WTX was first released in September 1998 (1.0) and updated in February of 1999 (1.1). The specification and other information on WTX are available at the following Web site:
http://www.wtx.org.
The WTX form factor is designed to support
■ Future Intel-based 32- and 64-bit processor technologies
■ Dual processor motherboards
■ Future memory technologies
■ Future graphics technologies
■ Flex Slot I/O (double-wide PCI) cards
■ Deskside (tower) form factor
■ Rack mount capability
■ Easy accessibility to memory and expansion slots
■ High-capacity power supplies
Figure 4.20 shows a typical WTX system with the cover removed. Note that easy access is provided to internal components via pull out drawers and swinging side panels.
WTX introduces a new slot called the Flex Slot, which is really a double-wide PCI slot designed to
allow larger, more power hungry, multifunction cards to be utilized. The Flex Slot is primarily
designed for a removable, customizable I/O card for WTX systems. By using the Flex Slot, the I/O
signals are moved farther away from the processor, chipset, and memory in the system. This
allows for improved Electromagnetic Interference (EMI) performance because I/O connectors and
their associated cables are moved away from the strongest signal generators in the system. A Flex
Slot I/O card can include features such as PCI, audio, LAN, SCSI, serial and parallel ports, keyboard and mouse connections, USB, 1394, and system management features such as fan speed
control, all on a single card. Figure 4.21 shows an example Flex Slot I/O card for a WTX system.
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Chapter 4
Overhead System Closed
System Closed
Overhead System Open
System Open
Figure 4.20
Typical WTX system chassis showing internal layout and ease of access.
Figure 4.21
Flex Slot I/O card for a WTX system.
227
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WTX motherboards can be a maximum width of 14 inches (356mm) and a maximum length of
16.75 inches (425 mm), which is significantly larger than ATX. There are no minimum motherboard dimensions, so board designers are free to design smaller boards as long as they meet the
mounting criteria. Figure 4.22 shows WTX maximum board dimensions, sample connector locations, and mounting hole restrictions.
8.950
(227, 33)
3X
2.232
1.225
(56, 69) (31,12)
.000
(0)
-B-
156
(3, 96)
.800
(20, 32)
2.965 MAX
(75, 32)
1,239
(31, 47)
Flex Slot
I/O Card
Centerline
1.818
(46, 19)
Slot S1
Slot S2
-CSlot S1
Slot S2
.000
(0)
.313
(7, 94)
Slot S3
.800
(20, 32)
Slot S4
Slot S5
4.900
(124, 46)
Slot S6
Slot S7
5.002
(127, 05)
5.197
(132)
7.375
(187, 33)
Rear I/O Window
in Chassis
13,785 MAX
(350, 13)
13,600 MAX
(345, 41)
Figure 4.22
400 MAX
(10, 15)
WTX motherboard dimensions and sample connector layout.
The WTX specification offers flexibility by leaving motherboard mounting features and locations
undefined. Instead of defining exact screw hole positions, WTX motherboards must mount to a
standard mounting adapter plate, which must be supplied with the board. The WTX chassis is
designed to accept the mounting plate with attached motherboard and not just a bare board
alone. Figure 4.23 shows the WTX motherboard mounting plate dimensions.
The WTX specification also defines keep-out zones or areas over the motherboard that must be
free of any physical restrictions. This is to allow adequate clearance for tall or large items on the
motherboard, and for proper cooling as well. Figure 4.24 shows the motherboard and plate as it
would be installed in the system, along with the keep-out zones over the board.
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12.151
(308, 64)
13.831
(351, 31)
7.276
(184, 81)
2.401
(60, 99)
.000
.519
(0) (13, 18)
2.401 .000
(60, 99) (0)
.890
(22, 62)
See Detail A
.588
(14, 43)
.868
(22, 05)
.000
(0)
.800
(20, 32)
2.499
(63, 47)
.368
(9, 35)
.000
(0)
5.410
(137, 4)
9X .500
(12, 7)
4.900
(124, 46)
5.433
(138)
C
C
Rear
9X .080
(2, 03)
11.410
(298, 8)
11.433
(290, 4)
11.433
(290, 4)
12.151
(308, 64)
9X .500
(12, 7)
2.401
(60, 99)
Detail A
.080 MIN
(2, 00)
Board-Side View
Section C-C
Figure 4.23
WTX motherboard mounting plate.
Zone
4
Zone
4
Zone
4
Zone
3
Zone
3
Zone
2
Zone
2
Zone
1
Figure 4.24
Zone
1
Typical WTX chassis showing board installation and keep-out zones.
229
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To run a heavy-duty WTX system, new power supply designs are required. WTX specifically
defines two power supply form factors and power levels in order to meet the power requirements
of WTX systems. They are single fan 350w nominal and dual fan 850w nominal units respectively. The single fan power supply is intended for the lower power (around 350w) configurations
of WTX systems. The dual fan power supply is for higher power configured workstations (up to
around 850w). These will normally be supplied with the chassis, and are mounted on a swing out
panel on one of the chassis sides.
With WTX we now have five industry standard form factors. Listed in order of cost/power from
most to least they are as follows:
■ WTX—For mid- to high-end workstations/servers
■ ATX (and mini-ATX)—For power users, enthusiasts, low-end servers/workstations, higherend home systems
■ NLX—For corporate desktop, business workstations
■ Micro-ATX—For midrange home systems, entertainment systems
■ Flex-ATX—For low-end home systems, starter PCs, PC-based appliances
As you can see, WTX isn’t a replacement for ATX, it is for much more expensive and much
higher end type systems than ATX.
Proprietary Designs
Motherboards that are not one of the standard form factors such as Full-sized or Baby-AT, ATX,
mini-ATX, micro-ATX, or NLX are deemed proprietary. Most people purchasing PCs should avoid
proprietary designs because they do not allow for a future motherboard, power supply, or case
upgrade, which limits future use and serviceability of the system. To me, proprietary systems are
disposable PCs, because you can neither upgrade them, nor can you easily repair them. The problem is that the proprietary parts can only come from the original system manufacturer, and they
usually cost many times more than non-proprietary parts. This means that after your proprietary
system goes out of warranty, it is not only un-upgradable, but it is also essentially no longer
worth repairing. If the motherboard or any component on it goes bad, you will be better off purchasing a completely new standard system than paying five times the normal price for a new proprietary motherboard. In addition, a new motherboard in a standard form factor system would be
one or more generations newer and faster than the one you would be replacing. In a proprietary
system, the replacement board would not only cost way too much, but it would be the same as
the one that failed.
Note that it might be possible to perform limited upgrades to older systems with proprietary
motherboards, in the form of custom (non-OEM) processor replacements with attached voltage
regulators, usually called “overdrive” chips. Unfortunately these often overtax the board, power
supply, and other components in the system, and because the board was not originally designed
to work with them, they usually don’t perform up to the standards of a less expensive new
processor and motherboard combination. As such, I normally recommend upgrading the motherboard and processor together—something that can’t be done with a proprietary system.
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Most proprietary systems will still allow for disk drive, memory, or other simple upgrades, but
even those can be limited because of board design and BIOS issues. The popular LPX motherboard design is at the heart of most proprietary systems. These systems are or were sold primarily
in the retail store channel. This class of system has traditionally been dominated by Compaq and
Packard Bell, and, as such, virtually all their systems have the problems inherent with their proprietary designs.
Some of these manufacturers seem to go out of their way to make their systems as physically
incompatible as possible with any other system. Then, replacement parts, repairs, and upgrades
are virtually impossible to find—except, of course, from the original system manufacturer and at
a significantly higher price than the equivalent part would cost to fit a standard PC-compatible
system.
For example, if the motherboard in my current ATX form factor system (and any system using a
Baby-AT motherboard and case) dies, I can find any number of replacement boards that will bolt
directly in—with my choice of processors and clock speeds—at great prices. If the motherboard
dies in a newer Compaq, Packard Bell, Hewlett-Packard, or other proprietary form factor system,
you’ll pay for a replacement available only from the original manufacturer, and you have little or
no opportunity to select a board with a faster or better processor than the one that failed. In
other words, upgrading or repairing one of these systems via a motherboard replacement is difficult and usually not cost-effective.
Systems sold by the leading mail-order suppliers such as Dell, Gateway, Micron, and others are
available in industry standard form factors such as ATX, micro-ATX, and NLX. This allows for
easy upgrading and system expansion in the future. These standard factors allow you to replace
your own motherboards, power supplies, and other components easily and select components
from any number of suppliers other than where you originally bought the system.
Backplane Systems
One type of proprietary design is the backplane system. These systems do not have a motherboard in the true sense of the word. In a backplane system, the components normally found on a
motherboard are located instead on an expansion adapter card plugged into a slot.
In these systems, the board with the slots is called a backplane, rather than a motherboard.
Systems using this type of construction are called backplane systems.
Backplane systems come in two main types—passive and active. A passive backplane means the
main backplane board does not contain any circuitry at all except for the bus connectors and
maybe some buffer and driver circuits. All the circuitry found on a conventional motherboard is
contained on one or more expansion cards installed in slots on the backplane. Some backplane
systems use a passive design that incorporates the entire system circuitry into a single mothercard. The mothercard is essentially a complete motherboard that is designed to plug into a slot in
the passive backplane. The passive backplane/mothercard concept allows the entire system to be
easily upgraded by changing one or more cards. Because of the expense of the high-function
mothercard, this type of system design is rarely found in PC systems. The passive backplane
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design does enjoy popularity in industrial systems, which are often rack-mounted. Some highend file servers also feature this design. Figure 4.25 shows Pentium II/III card-based systems for
passive backplane systems. Figure 4.26 shows a rack-mount chassis with a passive backplane.
Pentium II card-based
motherboard
c
Pentium III card-based
motherboard
Figure 4.25 Pentium and Pentium II/III card-based motherboards (mothercards) for passive backplane systems.
19 Din
(482.6mm)
4.0 Din
(101.8mm)
6 Din
(176.8mm)
5.25 Din
(5.7mm)
10.00 Din
(276.8mm)
6 Din
(176.8mm)
7.2 Din
(164.4mm)
4.0 Din
(102.2mm)
4.3 Din
(101.6mm)
17 Din
(432mm)
Figure 4.26
A rack-mount chassis with passive backplane.
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Passive backplane systems with mothercards (often called single-board computers) are by far the
most popular backplane design. They are used in industrial or laboratory type systems, and are
normally rack mountable. They usually have a large number of slots, extremely heavy-duty power
supplies, and feature high-capacity, reverse flow cooling designed to pressurize the chassis with
cool, filtered air.
An active backplane means the main backplane board contains bus control and usually other circuitry as well. Most active backplane systems contain all the circuitry found on a typical motherboard except for what is then called the processor complex. The processor complex is the name of
the circuit board that contains the main system processor and any other circuitry directly related
to it, such as clock control, cache, and so forth. The processor complex design allows the user to
easily upgrade the system later to a new processor type by changing one card. In effect, it
amounts to a modular motherboard with a replaceable processor section.
Many large PC manufacturers have built systems with an active backplane/processor complex.
Both IBM and Compaq, for example, have used this type of design in some of their high-end
(server class) systems. This allows an easier and generally more affordable upgrade than the passive backplane/mothercard design because the processor complex board is usually much cheaper
than a mothercard. Unfortunately, because there are no standards for the processor complex
interface to the system, these boards are proprietary and can only be purchased from the system
manufacturer. This limited market and availability causes the prices of these boards to be higher
than most complete motherboards from other manufacturers.
The motherboard system design and the backplane system design have advantages and disadvantages. Most original personal computers were designed as backplanes in the late 1970s. Apple and
IBM shifted the market to the now traditional motherboard with a slot-type design because this
type of system generally is cheaper to mass-produce than one with the backplane design. The
theoretical advantage of a backplane system, however, is that you can upgrade it easily to a new
processor and level of performance by changing a single card. For example, you can upgrade a
system’s processor just by changing the card. In a motherboard-design system, you often must
change the motherboard, a seemingly more formidable task. Unfortunately, the reality of the situation is that a backplane design is often much more expensive to upgrade. For example, because
the bus remains fixed on the backplane, the backplane design precludes more comprehensive
upgrades that involve adding local bus slots.
Another nail in the coffin of backplane designs is the upgradable processor. Starting with the 486,
Intel began standardizing the sockets or slots in which processors were to be installed, allowing a
single motherboard to support a wider variety of processors and system speeds. Because board
designs could be made more flexible, changing only the processor chip for a faster standard OEM
type (not one of the kludgy “overdrive” chips) is the easiest and generally most cost-effective way
to upgrade without changing the entire motherboard. To allow processor upgrades, Intel has standardized on a number of different types of CPU sockets and slots that allow for upgrading to any
faster processors designed to fit the same common socket or slot.
Because of the limited availability of the processor-complex boards or mothercards, they usually
end up being more expensive than a complete new motherboard that uses an industry-standard
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form factor. The bottom line is that unless you have a requirement for a large capacity industrial
or laboratory type system, especially one that would be rack mounted, you are better off sticking
with standard ATX form factor PCs. They will certainly be far less expensive.
Motherboard Components
A modern motherboard has several components built in, including various sockets, slots, connectors, chips, and so on. This section examines the components found on a typical motherboard.
Most modern motherboards have at least the following major components on them:
■ Processor socket/slot
■ Chipset (North and South Bridges)
■ Super I/O chip
■ ROM BIOS (Flash ROM)
■ SIMM/DIMM/RIMM sockets
■ ISA/PCI/AGP bus slots
■ CPU voltage regulator
■ Battery
These components are discussed in the following sections.
Processor Sockets/Slots
The CPU is installed in a socket for all systems up to and including the Pentium Pro processor.
The Pentium II processors and beyond use a slot where the processor card or cartridge plugs in.
Starting with the 486 processors, Intel designed the processor to be a user installable and replaceable part, and developed standards for CPU sockets that would allow different models of the
same basic processor to plug in. These socket specifications were numbered and based on the
socket or slot number you have on your motherboard. This means that you will know exactly
what types of processors can be installed.
√√ See “Processor Sockets,” 74.
Sockets for processors prior to the 486 were not numbered, and interchangeability was limited.
Table 4.2 shows the relationship between the various processor sockets/slots and the chips
designed to go into them.
Table 4.2
CPU Socket Specifications
Socket
Number
Pins
Pin Layout
Voltage
Supported Processors
Socket 1
169
17×17 PGA
5v
486 SX/SX2, DX/DX2*,
DX4 OverDrive
Socket 2
238
19×19 PGA
5v
486 SX/SX2, DX/DX2*,
DX4 OverDrive,
486 Pentium OverDrive
Socket 3
237
19×19 PGA
5v/3.3v
486 SX/SX2, DX/DX2, DX4,
486 Pentium OverDrive, 5x86
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Chipsets
Socket
Number
Pins
Pin Layout
Chapter 4
Voltage
Supported Processors
Pentium 60/66, OverDrive
Socket 4
273
21×21 PGA
5v
Socket 5
320
37×37 SPGA
3.3v/3.5v
Pentium 75-133, OverDrive
Socket 6**
235
19×19 PGA
3.3v
486 DX4, 486 Pentium OverDrive
Socket 7
321
37×37 SPGA
VRM
Pentium 75-266+, MMX, OverDrive,
6x86, K6
Socket 8
387
dual pattern SPGA
Auto VRM
Pentium Pro
Socket PGA370
370
37×37 SPGA
Auto VRM
PGA Celeron, future PIII
Slot 1
242
SEC/SEP Slot
Auto VRM
Pentium II, SEP Celeron, Pentium III
Slot 2/SC330
330
SEC Slot
Auto VRM
Pentium II Xeon, Pentium III Xeon
235
*Non-OverDrive DX4 also can be supported with the addition of an aftermarket 3.3v voltage regulator adapter.
**Socket 6 was a proposed standard only and was never actually implemented in any systems.
PGA = Pin Grid Array.
SPGA = Staggered Pin Grid Array.
VRM = Voltage Regulator Module.
SEC = Single Edge Contact cartridge.
SEP = Single-Edge Processor package (Pentium II without the plastic cartridge, for example, Celeron)
Chipsets
When the first PC motherboards were created by IBM, they used several discrete chips to complete the design. Besides the processor and optional math coprocessor, there were many other
components required to complete the system. These other components included things such as
the clock generator, bus controller, system timer, interrupt and DMA controllers, CMOS RAM and
clock, and the keyboard controller. There were also a number of other simple logic chips used to
complete the entire motherboard circuit, plus, of course, things such as the actual processor,
math coprocessor (floating-point unit), memory, and other parts. Table 4.3 lists all the primary
chip components used on the original PC/XT and AT motherboards.
Table 4.3
Primary Chip Components on Motherboards
Chip Function
PC/XT Version
AT Version
Processor
8088
80286
Math Coprocessor (Floating-Point Unit
8087
80287
Clock Generator
8284
82284
Bus Controller
8288
82288
System Timer
8253
8254
Low-order Interrupt Controller
8259
8259
High-order Interrupt Controller
—
8259
Low-order DMA Controller
8237
8237
High-order DMA Controller
-—
8237
CMOS RAM/Real-time Clock
—
MC146818
Keyboard Controller
8255
8042
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In addition to the processor/coprocessor, a six-chip set was used to implement the primary motherboard circuit in the original PC and XT systems. IBM later upgraded this to a nine-chip design
in the AT and later systems, mainly by adding additional Interrupt and DMA controller chips,
and the non-volatile CMOS RAM/Real-time Clock chip. All these motherboard chip components
came from Intel or an Intel-licensed manufacturer, except the CMOS/Clock chip, which came
from Motorola. To build a clone or copy of one of these IBM systems back would require all these
chips plus many smaller discrete logic chips to glue the design together, totaling to 100 or more
individual chips. This kept the price of a motherboard high, and left little room on the board to
integrate other functions.
In 1986, a company called Chips and Technologies introduced a revolutionary component called
the 82C206—the main part of the first PC motherboard chipset. This was a single chip that integrated into it all the functions of the main motherboard chips in an AT-compatible system. This
chip included the functions of the 82284 Clock Generator, 82288 Bus Controller, 8254 System
Timer, dual 8259 Interrupt Controllers, dual 8237 DMA Controllers, and even the MC146818
CMOS/Clock chip. Besides the processor, virtually all the major chip components on a PC motherboard could now be replaced by a single chip. Four other chips augmented the 82C206 acting
as buffers and memory controllers, thus completing virtually the entire motherboard circuit with
five total chips. This first chipset was called the CS8220 chipset by Chips and Technologies.
Needless to say, this was a revolutionary concept in PC motherboard manufacturing. Not only
did it greatly reduce the cost of building a PC motherboard, but it also made it much easier to
design a motherboard. The reduced component count meant the boards had more room for integrating other items formerly found on expansion cards. Later the four chips augmenting the
82C206 were replaced by a new set of only three chips, and the entire set was called the New
Enhanced AT (NEAT) CS8221 chipset. This was later followed by the 82C836 Single Chip AT
(SCAT) chipset, which finally condensed all the chips in the set down to a single chip.
The chipset idea was rapidly copied by other chip manufacturers. Companies such as Acer, Erso,
Opti, Suntac, Symphony, UMC, and VLSI each gained an important share of this market.
Unfortunately for many of them, the chipset market has been a volatile one, and many of them
have long since gone out of business. In 1993, VLSI had become the dominant force in the
chipset market and had the vast majority of the market share; by the next year, they, along with
virtually everybody else in the chipset market, would be fighting to stay alive. This is because a
new chipset manufacturer had come on the scene, and within a year or so of getting serious, they
were totally dominating the chipset market. That company is Intel, and since 1994 they have had
a virtual lock on the chipset market. If you have a motherboard built since 1994, chances are
good that it has an Intel chipset on it along with an Intel processor. There are very few chipset
competitors left, and the ones that are left are scratching for the lower end of the market. Today,
that would include primarily ALi (Acer Laboratories, Inc.), VIA Technologies, and SiS (Silicon integrated Systems). It is interesting to note that Chips and Technologies survived by changing
course to design and manufacture video chips, and found a niche in that market specifically for
laptop and notebook video chipsets. They were bought out by Intel in 1998 as a way for Intel to
get into the video chipset business.
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Intel Chipsets
You cannot talk about chipsets today without discussing Intel. They currently own well over 90
percent of the chipset market, and virtually 100 percent of the higher end Pentium II/III chipset
market. It is interesting to note that we probably have Compaq to thank for forcing Intel into the
chipset business in the first place!
The thing that really started it all was the introduction of the EISA bus designed by Compaq in
1989. At that time, they had shared the bus with other manufacturers in an attempt to make it a
market standard. However, they refused to share their EISA bus chipset—a set of custom chips
needed to implement this bus on a motherboard.
Enter Intel, who decided to fill the chipset void for the rest of the PC manufacturers wanting to
build EISA bus motherboards. As is well known today, the EISA bus failed to become a market
success except for the niche server business, but Intel now had a taste of the chipset business and
this they apparently wouldn’t forget. With the introduction of the 286 and 386 processors, Intel
became impatient with how long it took the other chipset companies to create chipsets around
their new processor designs; this delayed the introduction of motherboards that supported the
new processors. For example, it took more than two years after the 286 processor was introduced
for the first 286 motherboards to appear, and just over a year for the first 386 motherboards to
appear after the 386 had been introduced. Intel couldn’t sell their processors in volume until
other manufacturers made motherboards that would support them, so they thought that by
developing motherboard chipsets for a new processor in parallel with the new processor, they
could jumpstart the motherboard business by providing ready-made chipsets for the motherboard
manufacturers to use.
Intel tested this by introducing the 420 series chipsets along with their 486 processor in April of
1989. This allowed the motherboard companies to get busy right away, and it was only a few
months before the first 486 motherboards appeared. Of course, the other chipset manufacturers
weren’t happy; now they had Intel as a competitor, and Intel would always have their new
processor chipsets on the market first!
Intel then realized that they now made both processors and chipsets, which were 90 percent of
the components on a motherboard. What better way to ensure that motherboards were available
for their Pentium processor when it was introduced than by making their own motherboards as
well, and having these boards ready on the new processor’s introduction date. When the first
Pentium processor debuted in 1993, Intel also debuted the 430LX chipset and a fully finished
motherboard as well. Now not only were the chipset companies upset, but the motherboard companies weren’t too happy either. Intel was not only the major supplier of parts needed to build
finished boards (processors and chipsets), but Intel was now building and selling finished boards
as well. By 1994, Intel had not only dominated the processor market, but they had cornered the
chipset and motherboard markets as well.
Since then, Intel has remained on top in these markets, always introducing new chipsets and
motherboards to go with their new processors. Their success in processors prompted them to take
additional steps—making chipsets and then complete PC motherboards.
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Now as Intel develops new processors, they develop chipsets and even complete motherboards
simultaneously, which means they can be announced and shipped in unison. This eliminates the
delay between introducing new processors and having motherboards and systems be capable of
using them, which was common in the industry’s early days. This delay is virtually eliminated
today. It was amazing to me that on the day they introduced the first Pentium, Pentium II, and
Pentium III processors, not only were there new chipsets available to support them, but complete motherboards were available as well. That very day, you could call Dell, Gateway, or Micron
and order a complete “Intel” system using the new Intel processor, chipset, and motherboard.
This has not made companies such as Compaq (who still like to make their own motherboards
rather than purchase somebody else’s off-the-shelf product) very happy, to say the least.
First, with the advent of the Pentium, Pentium Pro, Pentium II, and now the Pentium III processor, not only do more than 90 percent of the systems sold use Intel processors, but their motherboards also most likely have an Intel chipset on them. In fact, their entire motherboard was most
likely made by Intel. In my seminars, I ask how many people in the class have Intel brand PCs.
Of course, Intel does not sell or market a PC under their own name, so nobody thinks they have
an “Intel brand” PC. But, if your motherboard was made by Intel, for all intents and purposes
you sure seem to have an Intel brand PC, as far as I am concerned. Does it really matter whether
Dell, Gateway, or Micron put that same Intel motherboard into a slightly different looking case
with their name on it?
Intel Chipset Model Numbers
Intel started a pattern of numbering their chipsets as follows:
Chipset Number
Processor Family
420xx
P4 (486)
430xx
P5 (Pentium)
440xx
P6 (Pentium Pro/Pentium II/III)
450xx
P6 Server (Pentium Pro/Pentium II/III Xeon)
The chipset numbers listed here are an abbreviation of the actual chipset numbers stamped on
the individual chips. For example, one of the current popular Pentium II/III chipsets is the Intel
440BX chipset, which really consists of two components, the 82443BX North Bridge and the
82371EX South Bridge. The North Bridge is so named because it is the connection between the
high-speed processor bus (66 or 100MHz) and the slower AGP (66MHz) and PCI (33MHz) buses.
The South Bridge is so named because it is the bridge between the PCI bus (33MHz) and the even
slower ISA bus (8MHz). By reading the number and letter combinations on the larger chips on
your motherboard, you can usually quickly identify the chipset your motherboard uses.
Most of Intel’s chipsets (and those of Intel’s competitors) are broken into a two-tiered architecture
incorporating a North Bridge and South Bridge section. The North Bridge is the main portion of
the chipset and incorporates the interface between the processor and the rest of the motherboard. The North Bridge components are what the chipset is named after, meaning that, for
example, what we call the 440BX chipset is actually derived from the fact that the actual North
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Bridge chip part number for that set is 82443BX. Figure 4.27 shows a sample motherboard (in
this case an Intel SE440BX-2) with the locations of all chips and components.
A
B
C
D E
F
G H I
J
FF
K
EE
DD
L
CC
M
N
O
BB
X
Z
AA
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
Y
W
V
U
- Wake on Ring connector*
- Yanaha YMF740 (DS1-L)
- Analog Devices AD1819A SoundPort
Codec*
- Wake on LAN connector*
- Legacy CD-ROM audio connector*
- CD-ROM Line In audio connector*
- Telephony connector*
- Auxiliary Line In audio connector*
- Video Line In audio connector*
- Back panel connectors
- 242-pin Slot-1 Pentium II/III
connector
- Active CPU fan heatsink power
connector (Fan 2)
- Intel 82443BX PCI/AGP (44BX North
Bridge) controller
- DIMM sockets
- Fan 1 power connector
T
S
P
Q
R
S
T
U
V
-
W
X
Y
Z
AA
BB
CC
DD
EE
FF
-
R
Q
S
Power supply main connector
Floppy drive connector
SCSI LED connector*
Primary/Secondary IDE connectors
Front panel connectors
Accelerated Graphics Port (AGP) slot
Intel 82371EB PCI ISA IDE Xcelerator
(PIIX4E South Bridge)
PCI ISA DMA functionality connector
3V Battery
SMSC FDC37M707 Super I/O controller
Flash BIOS
Configuration jumper
Integrated speaker
PCI slots
Fan 3 power connector
ISA slots
Chassis intrusion switch connector*
* = Optional features
Figure 4.27
Intel SE440BX-2 motherboard showing component locations. Used by permission of Intel.
The North Bridge contains the cache and main memory controllers and the interface between the
high-speed (33MHz, 50MHz, 66MHz, or 100MHz) processor bus and the 33MHz PCI (Peripheral
Component Interconnect) or 66MHz AGP (Accelerated Graphics Port) buses. Intel often refers to
the North Bridge of their more recent chipsets as the PAC (PCI/AGP Controller). The North
Bridge is essentially the main component of the motherboard and is the only motherboard circuit besides the processor that normally runs at full motherboard (processor bus) speed. Most
modern chipsets use a single-chip North Bridge; however, some of the older ones actually consisted of up to three individual chips to make up the complete North Bridge circuit.
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The South Bridge is the lower speed component in the chipset and has always been a single individual chip. The South Bridge is a somewhat interchangeable component in that different North
Bridge chipsets often are designed to use the same South Bridge component. This modular design
of the chipset allows for lower cost and greater flexibility for motherboard manufacturers. The
South Bridge connects to the 33MHz PCI bus and contains the interface to the 8MHz ISA bus. It
also normally contains the dual IDE hard disk controller interfaces, the USB (Universal Serial Bus)
interface, and even the CMOS RAM and clock functions. The South Bridge contains all the components that make up the ISA bus, including the interrupt and DMA controllers.
Let’s start by examining the Intel 486 motherboard chipsets and then work our way through the
latest Pentium II sets.
Intel’s Early 386/486 Chipsets
Intel’s first real PC motherboard chipset was the 82350 chipset for the 386DX and 486 processors.
This chipset was not very successful, mainly because the EISA bus was not very popular, and
because there were many other manufacturers making standard 386 and 486 motherboard
chipsets at the time. The market changed very quickly, and Intel dropped the EISA bus support
and introduced follow-up 486 chipsets that were much more successful.
Table 4.4 shows the Intel 486 chipsets.
Table 4.4
Intel 486 Motherboard Chipsets
Chipset
420TX
420EX
420ZX
Codename
Saturn
Aries
Saturn II
Date Introduced
Nov. ’92
March ’94
March ’94
Processor
5v 486
5v/3.3v 486
5v/3.3v 486
Bus Speed
up to 33 MHz
up to 50 MHz
up to 333 MHz
SMP (dual CPUs)
No
No
No
Memory Types
FPM
FPM
FPM
Parity/ECC
Parity
Parity
Parity
Max. Memory
128MMB
128MMB
160MMB
L2 Cache Type
Async
Async
Async
PCI Support
2.0
2.0
2.1
AGP Support
No
No
No
SMP = Symmetric Multiprocessing (Dual Processors)
FPM = Fast Page Mode
PCI = Peripheral Component Interconnect
AGP = Accelerated Graphics Port
Note: PCI 2.1 supports concurrent PCI operations.
Intel had pretty good success with their 486 chipsets. They had developed their current twotiered approach to system design even back then. This design is such that all Intel 486, Pentium,
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Pentium Pro, and Pentium II have been designed using two main components, which are commonly called the North Bridge and South Bridge.
Fifth-Generation (P5 Pentium Class) Chipsets
With the advent of the Pentium processor in March of 1993, Intel also introduced their first
Pentium chipset, the 430LX chipset (code-named Mercury). This was the first Pentium chipset on
the market and set the stage as Intel took this lead and ran with it. Other manufacturers took
months to a year or more to get their Pentium chipsets out the door. Since the debut of their
Pentium chipsets, Intel has dominated the chipset market with nobody even coming close. Table
4.5 shows the Intel Pentium motherboard chipsets.
Table 4.5
Intel Pentium Motherboard Chipsets (North Bridge)
Chipset
430LX
430NX
430FX
430MX
430HX
430VX
430TX
Codename
Mercury
Neptune
Triton
Mobile
Triton
Triton II
Triton III
n/a
Date Introduced
Mar. ‘93
Mar. ‘94
Jan. ‘95
Oct. ‘95
Feb. ‘96
Feb. ‘96
Feb. ‘97
Bus Speed
66 MHz
66MHz
66MHz
66MHz
66MHz
66MHz
66MHz
CPUs Supported
P60/66
P75+
P75+
P75+
P75+
P75+
P75+
SMP (dual CPUs)
No
Yes
No
No
Yes
No
No
Memory Types
FPM
FPM
FPM/
EDO
FPM/
EDO
FPM/
EDO
FPM/
EDO/
SDRAM
FPM/
EDO/
SDRAM
Parity/ECC
Parity
Parity
Neither
Neither
Both
Neither
Neither
Max. Memory
192MB
512MB
128MB
128MB
512MB
128MB
256MB
Max. Cacheable
192MB
512MB
64MB
64MB
512MB
64MB
64MB
L2 Cache Type
Async
Async
Async/
Pburst
Async/
Pburst
Async/
Pburst
Async/
Pburst
Async/
Pburst
PCI Support
2.0
2.0
2.0
2.0
2.1
2.1
2.1
AGP Support
No
No
No
No
No
No
No
South Bridge
SIO
SIO
PIIX
MPIIX
PIIX3
PIIX3
PIIX4
SMP = Symmetric Multiprocessing (Dual Processors)
FPM = Fast Page Mode
EDO = Extended Data Out
BEDO = Burst EDO
SDRAM = Synchronous Dynamic RAM
Note
PCI 2.1 supports concurrent PCI operations.
Table 4.6 shows all the applicable Intel South Bridge chips, which are the second part of the modern Intel motherboard chipsets.
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Intel South Bridge Chips
Chip Name
SIO
PIIX
PIIX3
PIIX4
PIIX4E
ICH0
ICH
Part Number
82378IB
/ZB
82371FB
82371SB
82371AB
82371EB
82801AB
82801AA
IDE Support
None
BMIDE
BMIDE
UDMA-33
UDMA-33
UDMA-33
UDMA-66
USB Support
None
None
Yes
Yes
Yes
Yes
Yes
CMOS/Clock
No
No
No
Yes
Yes
Yes
Yes
Power
Management
SMM
SMM
SMM
SMM
SMM/
ACPI
SMM/
ACPI
SMM/
ACPI
SIO = System I/O
PIIX = PCI ISA IDE Xcelerator
ICH = I/O Controller Hub
USB = Universal Serial Bus
IDE = Integrated Drive Electronics (AT Attachment)
BMIDE = Bus Master IDE
UDMA = Ultra-DMA IDE
SMM = System Management Mode
ACPI = Advanced Configuration and Power Interface
The following sections detail all the Pentium motherboard chipsets and their specifications.
Intel 430LX (Mercury)
The 430LX was introduced in March of 1993, concurrent with the introduction of the first
Pentium processors. This chipset was only used with the original Pentiums, which came in
60MHz and 66MHz versions. These were 5v chips and were used on motherboards with Socket 4
processor sockets.
√√ See “Processor Sockets,” p. 79.
√√ See “First-Generation Pentium Processor,” p. 133.
The 430LX chipset consisted of three total chips for the North Bridge portion. The main chip was
the 82434LX system controller. This chip contained the processor-to-memory interface, cache
controller, and PCI bus controller. There was also a pair of PCI bus interface accelerator chips,
which were identical 82433LX chips.
The 430LX chipset was noted for the following:
■ Single processor
■ Support for up to 512KB of L2 cache
■ Support for up to 192MB of standard DRAM
This chipset died off along with the 5v 60/66MHz Pentium processors.
Intel 430NX (Neptune)
Introduced in March of 1994, the 430NX was the first chipset designed to run the new 3.3v second generation Pentium processor. These were noted by having Socket 5 processor sockets, and
an on-board 3.3v/3.5v voltage regulator for both the processor and chipset. This chipset was primarily designed for Pentiums with speeds from 75MHz to 133MHz, although mostly it was used
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with 75MHz to 100MHz systems. Along with the lower voltage processor, this chipset ran faster,
cooler, and more reliably than the first-generation Pentium processor and the corresponding 5v
chipsets.
√√ See “CPU Operating Voltages,” p. 91.
√√ See “Second-Generation Pentium Processor,” p. 134.
The 430NX chipset consisted of three chips for the North Bridge component. The primary chip
was the 82434NX, which included the cache and main memory (DRAM) controller and the control interface to the PCI bus. The actual PCI data was managed by a pair of 82433NX chips called
local bus accelerators. Together, these two chips, plus the main 82434NX chip, constituted the
North Bridge.
The South Bridge used with the 430NX chipset was the 82378ZB System I/O (SIO) chip. This
component connected to the PCI bus and generated the lower speed ISA bus.
The 430NX chipset introduced the following improvements over the Mercury (430LX) chipset:
■ Dual processor support
■ Support for 512MB of system memory (up from 192MB for the LX Mercury chipset)
This chipset rapidly became the most popular chipset for the early 75MHz to 100MHz systems,
overshadowing the older 60MHz and 66MHz systems that used the 430LX chipset.
Intel 430FX (Triton)
The 430FX (Triton) chipset rapidly became the most popular chipset ever, after it was introduced
in January of 1995. This chipset is noted for being the first to support EDO (Extended Data Out)
memory, which also became popular at the time. EDO was slightly faster than the standard FPM
(Fast Page Mode) memory that had been used up until that time, but cost no more than the
slower FPM. Unfortunately, while being known for faster memory support, the Triton chipset was
also known as the first Pentium chipset without support for parity checking for memory. This
was a major blow to PC reliability, although many did not know it at the time.
◊◊ See “EDO RAM,” p. 427.
◊◊ See “Parity Checking,” p. 459.
The Triton chipset lacked not only parity support from the previous 430NX chipset, but it also
would only support a single CPU. The 430FX was designed as a low-end chipset, for home or
non–mission-critical systems. As such, it did not replace the 430NX, which carried on in higher
end network file servers and other more mission-critical systems.
The 430FX consisted of a three-chip North Bridge. The main chip was the 82437FX system controller that included the memory and cache controllers, CPU interface, and PCI bus controller,
along with dual 82438FX data path chips for the PCI bus. The South Bridge was the first PIIX
(PCI ISA IDE Xcelerator) chip that was the 82371FB. This chip acted not only as the bridge
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between the 33MHz PCI bus and the slower 8MHz ISA bus, but also incorporated for the first
time a dual-channel IDE interface. By moving the IDE interface off of the ISA bus and into the
PIIX chip, it was now effectively connected to the PCI bus, allowing for much faster Bus Master
IDE transfers. This was key in supporting the ATA-2 or Enhanced IDE interface for better hard
disk performance.
The major points on the 430FX are
■ Support for EDO memory
■ Support for higher speed—pipelined burst cache
■ PIIX South Bridge with high-speed Bus Master IDE
■ Lack of support for parity-checked memory
■ Only single CPU support
■ Supported only 128MB of RAM, of which only 64MB could be cached
That last issue is one that many people are not aware of. The 430FX chipset can only cache up to
64MB of main memory. This means that if you install more than 64MB of RAM in your system,
performance will suffer greatly. Now, many think this won’t be that much of a problem—after all,
they don’t normally run enough software to load past the first 64MB anyway. That is another
misunderstanding, because Windows 9x and NT/2000 (as well as all other protected mode operating systems including Linux, etc.) load from the top down. This means, for example, that if you
install 96MB of RAM (one 64MB and one 32MB bank), virtually all your software, including the
main operating system, will be loading into the non-cached region above 64MB. Only if you use
more than 32MB would you begin to see an improvement in performance. Try disabling the L2
cache via your CMOS setup to see how slow your system will run without it. That is the performance you can expect if you install more than 64MB of RAM in a 430FX-based system.
This lack of cacheable memory, plus the lack of support for parity or ECC (error correcting code)
memory, make this a non-recommended chipset in my book. Fortunately, this chipset became
obsolete when the more powerful 430HX was introduced.
Intel 430HX (Triton II)
The Triton II 430HX chipset was created by Intel as a true replacement for the powerful 430NX
chip. It added some of the high-speed memory features from the low-end 430FX, such as support
for EDO memory and pipeline burst L2 cache. It also retained dual-processor support. In addition
to supporting parity checking to detect memory errors, it also added support for ECC (error correcting code) memory to detect and correct single bit errors on-the-fly. And the great thing was
that this was implemented using plain parity memory.
This was a chipset suitable for high-end or mission-critical system use such as file servers; it also
worked well for lower end systems. Parity or ECC memory was not required—the chipset could
easily be configured to use less expensive, nonparity, noncorrecting memory as well.
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The HX chipset’s primary advantages over the FX are
■ Symmetric Multiprocessor (dual processor) support.
■ Support for ECC (error correcting code) and parity memory.
■ 512MB maximum RAM support (versus 128MB).
■ L2 cache functions over 512MB RAM versus 64MB (providing optional cache Tag RAM is
installed).
■ Memory transfers in fewer cycles overall.
■ PCI level 2.1 compliance that allows concurrent PCI operations.
■ PIIX3 supports different IDE/ATA transfer speed settings on a single channel.
■ PIIX3 South Bridge component supports USB.
The memory problems with caching in the 430FX were corrected in the 430HX. This chipset
allowed for the possibility of caching the full 512MB of possible RAM as long as the correct
amount of cache tag was installed. Tag is a small cache memory chip used to store the index to
the data in the cache. Most 430HX systems shipped with a tag chip that could only manage
64MB of cached main memory, while you could optionally upgrade it to a larger capacity tag
chip that would allow for caching the full 512MB of RAM.
The 430HX chipset was a true one-chip North Bridge. It was also one of the first chips out in a
ball-grid array package, where the chip leads were configured as balls on the bottom of the chip.
This allowed for a smaller chip package than the previous PQFP (Plastic Quad Flat Pack)
packaging used on the older chips, and, because there was only one chip for the North Bridge, a
very compact motherboard was possible. The South Bridge was the PIIX3 (82371SB) chip, which
allowed for independent timing of the dual IDE channels. This meant that you could install two
different speed devices on the same channel and configure their transfer speeds independently.
Previous PIIX chips allowed both devices to work at the lowest common denominator speed supported by both. The PIIX3 also incorporated the USB for the first time on a PC motherboard.
Unfortunately at the time, there were no devices available to attach to USB, nor was there any
operating systems or driver support for the bus. USB ports were a curiosity at the time, and
nobody had a use for them.
◊◊ See “USB (Universal Serial Bus),” p. 892.
The 430HX supports the newer PCI 2.1 standard, which allowed for concurrent PCI operations
and greater performance. Combined with the support for EDO and pipelined burst cache, this
was perhaps the best Pentium chipset for the power user’s system. It offered not only excellent
performance, but with ECC memory it offered a truly reliable and stable system design.
The 430HX was the only modern Intel Pentium-class chipset to offer parity and error-corrected
memory support. This made it the recommended Intel chipset for mission-critical applications
such as file servers, database servers, business systems, and so on. Of course, today few would recommend using any type of Pentium system as a file server in lieu of a more powerful, and yet
not much more expensive, Pentium II/III system.
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As this chipset and most of the Pentium processors are being phased out, you should look toward
Pentium II systems for this kind of support.
Intel 430VX (Triton III)
The 430VX chipset never had an official code-name, although many in the industry began calling it the Triton III. The 430VX was designed to be a replacement for the low-end 430FX chipset.
It was not a replacement for the higher powered 430HX chipset. As such, the VX has only one
significant technical advantage over the HX, but in almost all other respects is more like the
430FX than the HX.
The VX has the following features:
■ Support for 66MHz SDRAM (synchronous DRAM)
■ No parity or ECC memory support
■ Single processor only
■ Supports only 128MB RAM
■ Supports only 64MB of cached RAM
Although the support for SDRAM is a nice bonus, the actual speed derived from such memory is
limited. This is because with a good L2 cache, there will only be a cache miss about 5 percent of
the time the system is reading or writing memory, which means that the cache performance is
actually more important than main memory performance. This is why most 430HX systems are
faster than 430VX systems even though the VX can use faster SDRAM memory. Also, note that
because the VX was designed as a low-end chipset for low-cost retail systems, most of them
would never see any SDRAM memory anyway.
Like with the 430FX, the VX has the limitation of being capable to cache only 64MB of main
memory. With the memory price crash of 1996 bringing memory prices down to where more
than 64MB is actually affordable for most people, and with Windows software using more and
more memory, this is really becoming a limitation.
The 430VX chipset was rapidly made obsolete in the market by the 430TX chipset that followed.
Intel 430TX
The 430TX chipset never had a code-name that I am aware of; however, some persisted in calling
it the Triton IV. The 430TX was Intel’s last Pentium chipset. It was designed not only to be used
in desktop systems, but to replace the 430MX mobile Pentium chipset for laptop and notebook
systems.
The 430TX has some refinements over the 430VX, but, unfortunately, it still lacks support for
parity or ECC memory, and retains the 64MB cacheable RAM limitation of the older FX and VX
chipsets. The 430TX was not designed to replace the high-end 430HX chipset, which still
remained the chipset of choice for mission-critical systems. This is probably because of Intel’s deemphasizing of the Pentium; they are trying to wean us from Pentium processors and force the
market—especially for higher end mission-critical systems—to the more powerful Pentium II/III.
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The TX chipset features include the following:
■ 66MHz SDRAM support
■ Cacheable memory still limited to 64MB
■ Support for Ultra-ATA, or Ultra-DMA 33 (UDMA) IDE transfers
■ Lower power consumption for mobile use
■ No parity or ECC memory support
■ Single processor only
◊◊ See “ATA/ATAPI-4,” p. 526
Because the Pentium processor has been relegated to low-end system use only, the fact that it
lacks parity or ECC memory support, as well as the lack of support for cacheable memory over
64MB, has not been much of a problem for the market for which this chipset is intended. You
should not use it for business-class systems, especially those that are mission-critical.
Those seeking a true high-performance chipset and a system that is robust—and which has support for mission-critical features such as ECC memory or for caching more than 64MB of memory—should be looking at Pentium II systems and not the lowly Pentium. Intel has recently
stopped all further Pentium processor manufacturing and is only continuing to sell what they
have in inventory.
Third-Party (Non-Intel) P5 Pentium Class Chipsets
VIA Technologies
VIA Technologies, Inc. was founded in 1987, and has become a major designer of PC motherboard chipsets. VIA employs state-of-the-art manufacturing capability through foundry relationships with leading silicon manufacturers, such as Toshiba and Taiwan Semiconductor
Manufacturing Corporation.
Apollo VP-1
The VT82C580VP Apollo VP-1 is a four-chip set released in October of 1995 and used in older
Socket 5 and Socket 7 systems. The Apollo VP-1 is an equivalent alternative to the Intel 430VX
chipset, and features support for SDRAM, EDO, or Fast Page Mode memory as well as pipelineburst SRAM cache. The VP-1 consists of the VT82C585VP 208-pin PQFP (Plastic Quad Flat Pack),
two VT82C587VP 100-pin PQFP chips acting as the North Bridge, and the VT82C586 208-pin
PQFP South Bridge chip.
Apollo VP2
The two-chip Apollo VP2 chipset was released in May of 1996. The VP2 is a high-performance
Socket 7 chipset including several features over the previous VP-1 chipset. The VP2 adds support
for ECC (error correcting code) memory over the VPX. The VP2 has also been licensed by AMD as
their AMD 640 chipset. Motherboards using the Apollo VP2 can support P5 class processors,
including the Intel Pentium and Pentium MMX, AMD K5 and K6, and Cyrix/IBM 6x86 and
6x86MX (MII) processors.
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The VP2 chipset consists of the VT82C595 328 pin BGA (Ball Grid Array) package North Bridge
chip, which supports up to 2MB of L2 cache and up to 512MB DRAM. Additional performancerelated features include a fast DRAM controller with support for SDRAM, EDO, BEDO, and FPM
DRAM types in mixed combinations with 32/64-bit data bus widths and row and column
addressing, a deeper buffer with enhanced performance, and an intelligent PCI bus controller
with Concurrent PCI master/CPU/IDE (PCI 2.1) operations. For data integrity and server use, the
VP2/97 incorporates support for ECC or parity memory.
The Apollo VP2 features the VIA VT82C586B PCI-IDE South Bridge controller chip, which complies with the Microsoft PC97 industry specification by supporting ACPI/OnNow, Ultra DMA/33,
and USB technologies.
Apollo VPX
The VT82C580VPX Apollo VPX is a four-chip set for Socket 7 motherboards released in December
of 1996. The Apollo VPX is functionally equivalent to the Intel 430TX chipset, but also has specific performance enhancements relative to the 430TX. The VPX was designed as a replacement
for the VP-1 chipset, and is an upgrade of that set designed to add support for the newer AMD
and Cyrix P5 processors.
The Apollo VPX consists of the VT82C585VPX North Bridge and VT82C586B South Bridge chips.
There are also two 208-pin PQFP frame buffers that go with the North Bridge memory interface.
The Apollo VPX/97 features the VIA VT82C586B PCI-IDE South Bridge controller chip that complies with the Microsoft PC97 industry standard by supporting ACPI/OnNow, Ultra-DMA/33, and
USB technologies. VIA also offers a non-PC97 version of the Apollo VPX that includes the older
VT82C586A South Bridge and which was used in more entry-level PC designs.
Motherboards using the Apollo VPX can support P5 class processors, including the Intel Pentium
and Pentium MMX, AMD K5 and K6, and Cyrix/IBM 6x86 and 6x86MX (MII) processors. To
enable proper implementation of the Cyrix/IBM 6x86 200+ processor, the chipset features an
asynchronous CPU bus that operates at either 66 or 75MHz speeds. The Apollo VPX is an upgrade
over the Apollo VP-1 with the additional feature of Concurrent PCI master/CPU/IDE operations
(PCI 2.1). The VPX also supports up to 2MB of L2 cache and up to 512MB DRAM.
Apollo VP3
The Apollo VP3 is one of the first P5 class chipsets to implement the Intel AGP (Advanced
Graphics Port) specification. Intel offers that interface with their Pentium II (P6) class chipsets.
This allows a higher performance Socket 7 motherboard to be built that can accept the faster AGP
video cards. The Socket 7 interface allows P5 class processors such as the Intel Pentium and
Pentium MMX, AMD K5 and K6, and Cyrix/IBM 6x86 and 6x86MX (MII) to be utilized.
The Apollo VP3 chipset consists of the VT82C597 North Bridge system controller (472-pin BGA)
and the VT82C586B South Bridge (208-pin PQFP). The VT82C597 North Bridge provides superior
performance between the CPU, optional synchronous cache, DRAM, AGP bus, and the PCI bus
with pipelined, burst, and concurrent operation. The VT82C597 complies with the Accelerated
Graphics Port Specification 1.0 and features a 66MHz master system bus.
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Apollo MVP3
The Apollo MVP3 adds to the VP3 chip by supporting the new Super-7 100MHz Socket-7 specification. This allows the newer high-speed P5 processors such as the AMD K6 and Cyrix/IBM MII
processors to be supported. The Apollo MVP3 chipset is a two-chip chipset that consists of the
VT82C598AT North Bridge system controller and the VT82C586B South Bridge. The VT82C598AT
chip is a 476-pin BGA (Ball Grid Array) package and the VT82C586B chip is a 208-pin PQFP
(Plastic Quad Flat Pack) package.
The VT82C598AT North Bridge chip includes the CPU-to-PCI bridge, the L2 cache and buffer
controller, the DRAM controller, the AGP interface, and the PCI IDE controller. The VT82C598AT
North Bridge provides superior performance between the CPU, optional synchronous cache,
DRAM, AGP bus, and the PCI bus with pipelined, burst, and concurrent operation. The DRAM
controller supports standard Fast Page Mode (FPM), EDO, SDRAM, and DDR (Double Data Rate)
SDRAM. The VT82C598AT complies with the Accelerated Graphics Port Specification 1.0 and features support for 66/75/83/100MHz CPU bus frequencies and the 66MHz AGP bus frequency.
The VT82C586B South Bridge includes the PCI-to-ISA bridge, ACPI support, SMBus, the USB
host/hub interface, the Ultra-33 IDE Master controller, PS/2 Keyboard/Mouse controller, and the
I/O controller. The chip also contains the keyboard and PS/2 mouse controller.
This chipset is closest to the Intel 430TX in that it supports Socket 7 chips (Pentium and P5-compatible processors), SDRAM DIMM memory, and is physically a two-chip set. It differs mainly in
that it allows operation at speeds up to 100MHz and supports AGP—features only available with
the Pentium II boards and chipsets from Intel. This is an attempt to make the Socket 7 motherboards and processors more competitive with the lower-end Pentium II chips such as the Celeron.
The South Bridge is compatible with the newer Intel PIIX4e in that it includes UDMA IDE, USB,
CMOS RAM, plus ACPI 1.0 power management.
One big benefit over the Intel 430TX is support for ECC (error correcting code) memory or parity
checking can be selected on a bank-by-bank basis, which allows mixing of parity and ECC modules. The 430TX from Intel doesn’t support any ECC or parity functions at all. Memory timing
for FPM is X-3-3-3, whereas EDO is X-2-2-2, and SDRAM is X-1-1-1, which is similar to the Intel
430TX.
Another benefit over the 430TX is in memory cacheability. The 430TX allows caching up to only
64MB of main memory, a significant limitation in higher end systems. The maximum cacheable
range is determined by a combination of cache memory size and the number of cache tag bits
used. The most common L2 cache sizes will be 512KB or 1MB of L2 cache on the motherboard,
allowing either 128MB or 256MB of main memory to be cached. The maximum configuration of
2MB of L2 cache will allow up to 512MB of main memory to be cacheable. Intel solves this in the
Pentium II by including sufficient cache tag RAM in the L2 cache built in to the Pentium II
processors to allow either 512MB of main memory or 4GB of main memory to be cached.
The MVP3 seems to be the chipset of choice in the higher end Socket 7 motherboards from DFI,
FIC, Tyan, Acer, and others.
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Acer Laboratories, Inc (Ali)
Acer Laboratories, Inc. was originally founded in 1987 as an independent research and development center for the Acer Group. In 1993, ALi separated financially and legally from Acer Inc. and
became a member company of the Acer Group. ALi has rapidly claimed a prominent position
among PC chipset manufacturers.
Aladdin IV
The Aladdin IV from Acer Labs is a two-chip set for P5 class processors consisting of the M1531
North Bridge and either an M1533 or M1543 South Bridge chip. The Aladdin IV supports all
Intel, AMD, Cyrix/IBM and other P5-class CPUs including the Intel Pentium and Pentium MMX,
AMD K5 and K6, and the Cyrix/IBM 6x86 and 6x86MX (MII) processors. The Aladdin IV is equivalent to the Intel 430TX chipset, with the addition of error-correcting memory support and
higher-speed 75MHz and 83.3MHz operation. Also, when using the M1543 South Bridge, an additional Super I/O chip is not necessary as those functions are included in the M1543 South Bridge.
The M1531 North Bridge is a 328-pin BGA (Ball Grid Array) chip that supports CPU bus speeds of
83.3 MHz, 75 MHz, 66 MHz, 60 MHz, and 50MHz. The M1531 also supports Pipelined-Burst
SRAM cache in sizes of up to 1MB, allowing either 64MB (with 8-bit Tag SRAM) or up to 512MB
(with 11-bit Tag SRAM) of cacheable main memory. FPM, EDO, or SDRAM main memory modules are supported for a total capacity of 1GB in up to four total banks. Memory timing is 6-3-3-3
for back-to-back FPM reads, 5-2-2-2 for back-to-back EDO reads, and 6-1-1-1 for back-to-back
SDRAM reads. For reliability and integrity in mission-critical or server applications, ECC (Error
Correcting Code) or parity is supported. PCI spec. 2.1 is also supported, allowing concurrent PCI
operations.
The M1533 South Bridge integrates ACPI support, two-channel Ultra-DMA 33 IDE master controller, two-port USB controller, and a standard Keyboard/Mouse controller. A more full-function
M1543 South Bridge is also available that has everything in the M1533 South Bridge plus all the
functions of a normally separate Super I/O controller. The M1543 integrates ACPI support, twochannel Ultra-DMA 33 IDE controller, two-port USB controller, and a standard keyboard/mouse
controller. Also included is an integrated Super I/O including a 2.88MB floppy disk controller,
two high-performance serial ports, and a multi-mode parallel port. The serial ports incorporate
16550-compatible UARTs (Universal Asynchronous Receiver Transmitters) with 16-byte FIFO (First
In First Out) buffers and Serial Infra Red (SIR) capability. The multimode Parallel Port includes
support for Standard Parallel Port (SPP) mode, PS/2 bidirectional mode, Enhanced Parallel Port
(EPP) mode, and the Microsoft and Hewlett Packard Extended Capabilities Port (ECP) mode.
Aladdin V
The Acer Labs (ALi) Aladdin V Chipset is a two-chip set that consists of the M1541 North Bridge
chip and the M1543 South Bridge/Super I/O controller combo chip. The M1541 North Bridge is a
456-pin BGA package chip while the M1543 South Bridge is a 328-pin BGA package chip. The
M1541 chipset is similar to the previous M1532 chipset with the addition of higher speed (up to
100MHz) operation and AGP (Accelerated Graphics Port) support.
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The M1541 North Bridge includes the CPU-to-PCI bridge, the L2 cache and buffer controller, the
DRAM controller, the AGP interface, and the PCI controller. The M1541 supports the Super-7
high-speed 100MHz Socket 7 processor interface used by some of the newer AMD and Cyrix/IBM
P5 processors. It will also run the processor bus at 83.3MHz, 75MHz, 66MHz, 60MHz, and 50MHz
for backward compatibility. When running the CPU bus at 75MHz, the PCI bus only runs at
30MHz; however, when the CPU bus is running at 83.3MHz or 100MHz, the PCI bus will run at
full 33MHz PCI standard speed.
The M1541 also integrates enough cache Tag RAM (16K×10) internally to support 512KB of L2
cache, simplifying the L2 cache design and further reducing the number of chips on the motherboard. Cacheable memory is up to 512MB of RAM when using 512KB L2 cache and 1GB of RAM
when using 1MB of L2 cache. FPM, EDO, or SDRAM memory is supported, in up to four banks
and up to 1GB total RAM. ECC/Parity is also supported for mission-critical or fileserver applications to improve reliability. Memory timing is 6-3-3-3-3-3-3-3 for back-to-back FPM reads, 5-2-2-22-2-2-2 for back-to-back EDO reads, and 6-1-1-1-2-1-1-1 for back-to-back SDRAM reads. For more
information on memory timing, see chapter 6.
Finally, Accelerated Graphics Port (AGP) Interface specification V1.0 is supported, along with 1x
and 2x modes, allowing the latest graphics cards to be utilized.
The M1543 South Bridge and Super I/O combo chip includes ACPI support, the USB host/hub
interface, dual channel Ultra-DMA/33 IDE host interface, keyboard and mouse controller, and the
Super I/O controller. The built-in Super I/O consists of an integrated floppy disk controller, two
serial ports with infrared support, and a multimode parallel port.
Silicon integrated Systems (SiS)
Silicon integrated Systems (SiS) was formerly known as Symphony Labs and is one of the three
largest non-Intel PC motherboard chipset manufacturers.
5581 and 5582
The SiS5581 and 5582 chips are both 553-pin BGA package single-chip sets incorporating both
North and South Bridge functions. The SiS5582 is targeted for AT/ATX form factor motherboards
while the SiS5581 is intended to be used on LPX/NLX form factor boards. In all other ways, the
two North Bridge chips are identical. The SiS 5581/5582 is a single-chip set designed to be a highperformance, low-cost alternative that is functionally equivalent to Intel’s 430TX chipset. By having everything in a single chip, a low-cost motherboard can be produced.
The 5581/5582 consists of both North and South Bridge functions, including PCI to ISA bridge
function, PCI IDE function, Universal Serial Bus host/hub function, Integrated RTC, and
Integrated Keyboard Controller. These chips support a CPU bus speed of 50, 55, 60, 66, and
75MHz.
A maximum of 512KB of L2 cache is supported, with a maximum cacheable range of 128MB of
main memory. The maximum cacheable range is determined by a combination of cache memory
size, and the number of Tag bits used. The most common cache size that will allow caching of up
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to 128MB of RAM will be 512KB, although up to 384MB of RAM can technically be installed in
up to three total banks. Because this is designed for low-cost systems, ECC (Error Correcting
Code) or parity functions are not supported. Main memory timing is x-3-3-3 for FPM, while EDO
timing is x-2-2-2, and SDRAM timing is x-1-1-1.
The 5581/5582 chipset also includes Advanced Configuration and Power Interface (ACPI) power
management, a dual channel Ultra-DMA/33 IDE interface, USB controller, and even the CMOS
RAM and Real Time Clock (RTC). PCI v2.1 is supported that allows concurrent PCI operation;
however, AGP is not supported in this chipset.
5591 and 5592
The SiS 5591/5592 is a three-chip set consisting of either a 5591 or 5592 North Bridge chip along
with a SiS5595 South Bridge. The 5591/5592 North Bridge chips are both 3.3v 553-pin BGA package chips, while the 5595 South Bridge chip is a 5v 208-pin PQFP (Plastic Quad Flat Pack) package
chip. The SiS5591 North Bridge is targeted for ATX form factor motherboards while the SiS5592
version is intended to be used on the NLX form factor. In all other ways, the two North Bridge
chips are identical.
The 5591/5592 North Bridge chips include the Host-to-PCI bridge, the L2 cache controller, the
DRAM controller, the Accelerated Graphics Port interface, and the PCI IDE controller. The
SiS5595 South Bridge includes the PCI-to-ISA bridge, the ACPI/APM power management unit, the
Universal Serial Bus host/hub interface, and the ISA bus interface that contains the ISA bus controller, the DMA controllers, the interrupt controllers, and the Timers. It also integrates the
Keyboard controller and the Real Time Clock (RTC).
The 5591/5592 North Bridge chips support CPU bus speeds of up to 75MHz. They also support
up to 1MB of L2 cache allowing up to 256MB of main memory to be cacheable. The maximum
cacheable main memory amount is determined by a combination of cache memory size and the
number of Tag bits used. Most common cache sizes will be 512KB and 1MB. The 512KB cache
with 7 Tag bits will allow only 64M of memory to be cached, while 8 Tag bits will allow caching
of up to 128MB. With 1MB of cache onboard, the cacheable range is doubled to a maximum of
256MB.
A maximum of 256MB of total RAM is allowed in up to three banks. Both ECC and parity are
supported for mission-critical or file server applications. Main memory timing for FPM memory is
x-3-3-3, EDO timing is x-2-2-2, and SDRAM is x-1-1-1.
PCI specification 2.1 is supported at up to 33MHz, and AGP specification 1.0 is supported in both
1x and 2x modes. The separate 5595 South Bridge includes a dual-channel Ultra-DMA/33 interface and support for USB.
Sixth-Generation (P6 Pentium Pro/Pentium
II/III Class) Chipsets
Although Intel clearly dominated the Pentium chipset world, they are virtually the only game in
town for the Pentium Pro and Pentium II/III chipsets. The biggest reason for this is that since the
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253
Pentium first came out in 1993, Intel has been introducing new chipsets (and even complete
ready-to-go motherboards) simultaneously with their new processors. This makes it hard for anybody else to catch up. Another problem for other chipset manufacturers is that Intel has been
reluctant to license the Slot 1 and Socket 370 interface used by the Celeron and Pentium II/III
processors, while the Socket 7 interface used by the Pentium has been freely available for license.
Still, some licenses have been granted, and you should see other chipmakers developing Socket
370 or Slot 1 processors in the future. For now, Intel has most of the Celeron/Pentium II/III market to themselves.
Several of the third-party chipset manufacturers such as VIA Technologies, Acer Laboratories, Inc
(ALi), and Silicon integrated Systems (SiS) have recently introduced chipsets for Slot 1 or Socket
370 motherboards.
Note that because the Pentium Pro, Celeron, and Pentium II/III are essentially the same processor
with different cache designs, the same chipset can be used for Socket 8 (Pentium Pro), Socket 370
(Celeron), and Slot 1 (Celeron/Pentium II/III) designs. Of course, the newer P6 class chipsets are
optimized for the Slot 1/Socket 370 architecture and nobody is doing any new Socket 8 designs.
This is also true for the Pentium Pro, which is essentially obsolete compared to the
Celeron/Pentium II/III and is currently being used only in limited file server applications.
Although there are a few newcomers to the P6 chipset market, virtually all Pentium Pro, Celeron,
and Pentium II/III motherboards use Intel chipsets; their market share here is for all practical purposes near 100 percent.
The sixth-generation P6 (Pentium Pro/Celeron/Pentium II/III) motherboard chipsets continue
with the North Bridge/South Bridge design first debuted in the Pentium processor chipsets. In
fact, the South Bridge portion of the chipset is the same as that used in many of the Pentium
chipsets.
Table 4.7 shows the chipsets used on Pentium Pro motherboards.
Table 4.7
Pentium Pro Motherboard Chipsets (North Bridge)
Chipset
450KX
450GX
440FX
Codename
Orion
Orion Server
Natoma
Workstation Date
Introduced
Nov. 1995
Nov. 1995
May 1996
Bus Speed
66 MHz
66 MHz
66 MHz
SMP (dual CPUs)
Yes
Yes (4 CPUs)
Yes
Memory Types
FPM
FPM
FPM/EDO/BEDO
Parity/ECC
Both
Both
Both
Maximum Memory
8GB
1GB
1GB
L2 Cache Type
In CPU
In CPU
In CPU
Maximum Cacheable 1GB
1GB
1GB
PCI Support
2.0
2.1
2.0
(continues)
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Continued
Chipset
450KX
450GX
440FX
AGP Support
No
No
No
AGP Speed
n/a
n/a
n/a
South Bridge
various
various
PIIX3
SMP = Symmetric Multiprocessing (Dual Processors)
FPM = Fast Page Mode
EDO = Extended Data Out
BEDO = Burst EDO
SDRAM = Synchronous Dynamic RAM
Pburst = Pipeline Burst (Synchronous)
PCI = Peripheral Component Interconnect
AGP = Accelerated Graphics Port
SIO = System I/O
PIIX = PCI ISA IDE Xcelerator
Note
PCI 2.1 supports concurrent PCI operations.
For the Celeron and Pentium II/III motherboards, Intel offers the chipsets in Table 4.8.
Table 4.8
Celeron and Pentium II/III Motherboard Chipsets (North Bridge)
Chipset
440FX
440LX
440EX
440BX
Codename
Natoma
none
none
none
Date Introduced
May 1996
Aug. 1997
April 1998
April 199
Part Numbers
82441FX
82442FX
82443LX
82443EX
82443BX
Bus Speed
66 MHz
66 MHz
66 MHz
66/100 MHz
Optimum Processor
Pentium II
Pentium II
Celeron
Pentium II/III,
Celeron
SMP (dual CPUs)
Yes
Yes
No
Yes
Memory Types
FPM/EDO/BEDO
FPM/EDO/SDRAM
EDO/SDRAM
SDRAM
Parity/ECC
Both
Both
Neither
Both
Maximum Memory
1GB
1GB EDO/
512 MB
SDRAM
256MB
1GB
Memory Banks
4
4
2
4
PCI Support
2.1
2.1
2.1
2.1
AGP Support
No
AGP-2x
AGP-2x
AGP-2x
South Bridge
82371SB (PIIX3)
82371AB (PIIX4)
82371EB (PIIX4E)
82371EB (PIIX4E)
Chipset
440GX
450NX
440ZX
810
Codename
none
none
none
Whitney
Date Introduced
June 1998
June ‘98
November ‘98
April ‘99
Part Numbers
82443GX
82451NX
82452NX
82453NX
82454NX
82443ZX
82810/
82810DC100
82802AB/AC
Bus Speed
100 MHz
100 MHz
66/100 MHz*
66/100 MHz
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Chipset
440GX
450NX
440ZX
810
Optimum Processor
Pentium II/III,
Xeon
Pentium II/III,
Xeon
Celeron,
Pentium II/III
Celeron,
Pentium II/III
SMP (dual CPUs)
Yes
Yes, up to 4
No
No
Memory Types
SDRAM
FPM/EDO
SDRAM
SDRAM
Parity/ECC
Both
Both
Neither
Neither
Maximum Memory
2GB
8 GB
256 MB
256 MB
Memory Banks
4
4
2
2
PCI Support
2.1
2.1
2.1
2.2
AGP Support
AGP-2x
No
AGP-2x
Direct AGP
South Bridge
82371EB (PIIX4E)
82371EB (PIIX4E)
82371EB (PIIX4E)
82801AA/
AB (ICH/ICH0)
255
* Note the 440ZX is available in a cheaper 440ZX-66 version, which will only run 66MHz
SMP = Symmetric Multiprocessing (Dual Processors)
FPM = Fast Page Mode
PCI = Peripheral Component Interconnect
EDO = Extended Data Out
AGP = Accelerated Graphics Port
BEDO = Burst EDO
SIO = System I/O
SDRAM = Synchronous Dynamic RAM
PIIX = PCI ISA IDE Xcelerator
Pburst = Pipeline Burst (Synchronous)
ICH = I/O Controller Hub
Note
Pentium Pro, Celeron, and Pentium II/III CPUs have their secondary cache integrated into the CPU package.
Therefore, cache characteristics for these machines are not dependent on the chipset but are quite dependent on
the processor instead.
Most Intel chipsets are designed as a two-part system, using a North Bridge and a South Bridge
component. Often the same South Bridge component can be used with several different North
Bridge chipsets. Table 4.9 shows a list of all the current Intel South Bridge components and their
capabilities.
Table 4.9
Intel South Bridge Chips
Chip Name
SIO
PIIX
PIIX3
PIIX4
PIIX4E
ICH0
ICH
Part Number
82378IB
/ZB
82371FB
82371SB
82371AB
82371EB
82801AB
82801AA
IDE Support
None
BMIDE
BMIDE
UDMA-33
UDMA-33
UDMA-33
UDMA-66
USB Support
None
None
Yes
Yes
Yes
Yes
Yes
CMOS/Clock
No
No
No
Yes
Yes
Yes
Yes
Power
Management
SMM
SMM
SMM
SMM
SMM/
ACPI
SMM/
ACPI
SMM/
ACPI
SIO = System I/O
PIIX = PCI ISA IDE Xcelerator
ICH = I/O Controller Hub
USB = Universal Serial Bus
IDE = Integrated Drive Electronics (AT Attachment)
BMIDE = Bus Master IDE
UDMA = Ultra-DMA IDE
SMM = System Management Mode
ACPI = Advanced Configuration and Power Interface
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The following sections examine the P6 chipsets for both the Pentium Pro and Pentium II
processors.
Intel 450KX/GX (Orion Workstation/Server)
The first chipsets to support the Pentium Pro were the 450KX and GX, both code-named Orion.
The 450KX was designed for networked or standalone workstations; the more powerful 450GX
was designed for file servers. The GX server chipset was particularly suited to the server role, as it
supports up to four Pentium Pro processors for Symmetric Multiprocessing (SMP) servers, up to
8GB of four-way interleaved memory with ECC or parity, and two bridged PCI buses. The 450KX
is the workstation or standalone user version of Orion and as such it supports fewer processors
(one or two) and less memory (1GB) than the GX. The 450GX and 450KX both have full support
for ECC memory—a requirement for server and workstation use.
The 450GX and 450KX North Bridge is comprised of four individual chip components—an
82454KX/GX PCI Bridge, an 82452KX/GX Data Path (DP), an 82453KX/GX Data Controller (DC),
and an 82451KX/GX Memory Interface Controller (MIC). Options for QFP (Quad Flat Pack) or
BGA (Ball Grid Array) packaging were available on the PCI Bridge and the DP. BGA uses less space
on a board.
The 450’s high reliability is obtained through ECC from the Pentium Pro processor data bus to
memory. Reliability is also enhanced by parity protection on the processor bus, control bus, and
on all PCI signals. In addition, single-bit error correction is provided, thereby avoiding server
downtime because of spurious memory errors caused by cosmic rays.
◊◊ See “Parity and ECC,” p. 457.
Until the introduction of the following 440FX chipset, these were used almost exclusively in file
servers. After the debut of the 440FX, the expensive Orion chips all but disappeared due to their
complexity and high cost.
Intel 440FX (Natoma)
The first popular mainstream P6 (Pentium Pro or Pentium II) motherboard chipset was the
440FX, which was code-named Natoma. The 440FX was designed by Intel to be a lower cost and
somewhat higher performance replacement for the 450KX workstation chipset. It offered better
memory performance through support of EDO memory, which the prior 450KX lacked.
The 440FX uses half the number of components than the previous Intel chipset. It offers additional features such as support for the PCI 2.1 (Concurrent PCI) standard, Universal Serial Bus
(USB) support, and reliability through error checking and correction (ECC).
The Concurrent PCI processing architecture maximizes system performance with simultaneous
activity on the CPU, PCI, and ISA buses. Concurrent PCI provides increased bandwidth to better
support 2D/3D graphics, video and audio, and processing for host-based applications. ECC memory support delivers improved reliability to business system users.
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The main features of this chipset include
■ Support for up to 1GB of EDO memory
■ Full 1GB cacheability (based on the processor because the L2 cache and tag are in the CPU)
■ Support for USB
■ Support for BusMaster IDE
■ Full parity/ECC support
The 440FX consists of a two-chip North Bridge. The main component is the 82441FX PCI Bridge
and Memory controller, along with the 82442FX Data Bus accelerator for the PCI bus. This
chipset uses the PIIX3 82371SB South Bridge chip that supports high-speed busmaster DMA IDE
interfaces and USB, and it acts as the bridge between the PCI and ISA buses.
Note that this was the first P6 chipset to support EDO memory, but it lacked support for the
faster SDRAM. Also, the PIIX3 used with this chipset does not support the faster Ultra DMA IDE
hard drives.
The 440FX was the chipset used on the first Pentium II motherboards, which have the same basic
architecture as the Pentium Pro. The Pentium II was released several months before the chipset
that was supposedly designed for it was ready, and so early PII motherboards used the older
440FX chipset. This chipset was never designed with the Pentium II in mind, whereas the newer
440LX was optimized specifically to take advantage of the Pentium II architecture. For that reason, I normally recommended that people stay away from the original 440FX-based PII motherboards and wait for Pentium II systems that used the forthcoming 440LX chipset. When the new
chipset was introduced, the 440FX was quickly superseded by the improved 440LX design.
Intel 440LX
The 440LX quickly took over in the marketplace after it debuted in August of 1997. This was the
first chipset to really take full advantage of the Pentium II processor. Compared to the 440FX, the
440LX chipset offers several improvements:
■ Support for the new Advanced Graphics Port (AGP) video card bus
■ Support for 66MHz SDRAM memory
■ Support for the Ultra DMA IDE interface
■ Support for Universal Serial Bus (USB)
The 440LX rapidly became the most popular chip for all new Pentium II systems from the end of
1997 through the beginning of 1998.
Intel 440EX
The 440EX is designed to be a low-cost lower performance alternative to the 440LX chipset. It
was introduced in April 1998 along with the Intel Celeron low-end Pentium II processor. The
440EX lacks several features in the more powerful 440LX, including dual processor and ECC or
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parity memory support. This chipset is basically designed for low-end 66MHz bus-based systems
that use the new Intel Celeron low-end Pentium II processor. Note that boards with the 440EX
will fully support a full-blown Pentium II but lack some of the features of the more powerful
440LX or 440BX chipsets.
The main things to note about the 440EX are listed here:
■ Designed with a feature set tuned for the low-end PC market
■ Primarily for the Intel Celeron processor
■ Supports AGP
■ Does not support ECC or parity memory
■ Single processor support only
Although it is based on the core technology of the Intel 440LX, the 440EX is basically considered
a lower-feature, lower-reliability version of that chipset designed for non-mission-critical systems.
The 440EX consists of a 82443EX PCI AGP Controller (PAC) North Bridge component and the
new 82371EB (PIIX4E) South Bridge chip. Although this chipset is fine for most low-end use, I
would normally recommend the faster, more powerful, and more reliable (with ECC memory)
440BX instead.
Intel 440BX
The Intel 440BX chipset was introduced in April of 1998 and was the first chipset to run the
processor host bus (and basically the motherboard) at 100MHz. The 440BX was designed specifically to support the faster Pentium II/III processors at 350MHz, 400MHz, 450MHz, or 500MHz. A
mobile version of this chipset also is the first Pentium II/III chipset for notebook or laptop
systems.
The main change from the previous 440LX to the BX is that the 440BX chipset improves performance by increasing the bandwidth of the system bus from 66MHz to 100MHz. The chipset can
run at either 66- or 100MHz, allowing one basic motherboard design to support all Pentium II/III
processor speeds from 233MHz to 500MHz and beyond.
Intel 440BX highlights
■ Support for 100MHz SDRAM (PC100)
■ Support for both 100MHz or 66MHz system and memory bus designs
■ Support for up to 1GB of memory in up to four banks (four DIMMs)
■ Support for ECC (Error Correcting Code) memory
■ Support for ACPI (Advanced Configuration and Power Interface specification)
■ The first chipset to support the Mobile Intel Pentium II processor
◊◊ See “Mobile Pentium II,” p. 1218.
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The Intel 440BX consists of a single North Bridge chip called the 82443BX Host
Bridge/Controller, which is paired with a new 82371EB PCI-ISA/IDE Xcelerator (PIIX4E) South
Bridge chip. The new South Bridge adds support for the ACPI specification version 1.0. Figure
4.28 shows a typical system block diagram using the 440BX.
Pentium® II
Processor
Video
- DVD
- Camera
- VCR
Host Bus
- VMI
- Video Capture
2X AGP Bus
Graphics
Device
Pentium® II
Processor
82443BX
Host Bridge
66/100
MHz
Main
Memory
3.3V EDO &
SDRAM Support
Display
Graphics Local
Memory
PCI Slots
Encoder
Primary
PCI Bus
TV
(PCI Bus #0)
Video BIOS
System MGMT
(SM) Bus
2 IDE Ports
(Ultra DMA/33)
2 USB
Ports
USB
82371EB
(PIIX4E)
(PCI-to-ISA
Bridge
IO
APIC
ISA Slots
USB
ISA Bus
System BIOS
Figure 4.28
System block diagram using the Intel 440BX chipset.
The 440BX is currently the most popular high-end chipset in the Intel arsenal for standard desktop users. It offers superior performance and high reliability through the use of ECC (Error
Correcting Code), SDRAM (Synchronous DRAM), and DIMMs (Dual Inline Memory Modules).
Intel 440ZX and 440ZX-66
The 440ZX is designed to be a low-cost version of the 440BX. The 440ZX brings 66 or 100MHz
performance to entry-level Celeron and low-end Pentium II/III systems. The 440ZX is pin-compatible with the more expensive 440BX, meaning existing 440BX motherboards can be easily
redesigned to use this lower cost chipset.
Note that there are two versions of the 440ZX, the standard one, will run at 100MHz or 66MHz,
and the 440ZX-66, which will only run at the slower 66MHz.
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The features of the 440ZX include the following:
■ Optimized for the micro-ATX form factor
■ Support for Celeron and Pentium II/III processors at up to 100MHz bus speeds
■ The main differences from the 440BX include
• No parity or ECC memory support
• Only two banks of memory (two DIMMs) supported
• Maximum memory only 256MB
• Only runs up to 66MHz (440ZX-66)
The 440ZX is not a replacement for the 440BX; instead, it is designed to be used in less expensive
systems where the greater memory capabilities, performance, and data integrity functions (ECC
memory) of the 440BX are not needed.
Intel 440GX
The Intel 440GX AGPset is the first chipset optimized for high-volume midrange workstations
and lower cost servers. The 440GX is essentially a version of the 440BX that has been upgraded
to support the Slot 2 (also called SC330) processor slot for the Pentium II/III Xeon processor. The
440GX can still be used in Slot 1 designs as well. It also supports up to 2GB of memory, twice
that of the 440BX. Other than these items, the 440GX is essentially the same as the 440BX.
Because the 440GX is core-compatible with the 440BX, motherboard manufacturers will be able
to quickly and easily modify their existing Slot 1 440BX board designs into Slot 1 or 2 440GX
designs.
The main features of the 440GX include
■ Support for Slot 1 and Slot 2
■ Support for 100MHz system bus
■ Support for up to 2GB of SDRAM memory
This chipset allows for lower cost, high-performance workstations and servers using the Slot 2
based Xeon processors.
Intel 450NX
The 450NX chipset is designed for multiprocessor systems and standard high-volume servers
based on the Pentium II/III Xeon processor. The Intel 450NX chipset consists of four components: the 82454NX PCI Expander Bridge (PXB), 82451NX Memory and I/O Bridge Controller
(MIOC), 82452NX RAS/CAS Generator (RCG), and 82453NX Data Path Multiplexor (MUX).
The 450NX supports up to four Pentium II/III Xeon processors at 100MHz. Two dedicated PCI
Expander Bridges (PXBs) can be connected via the Expander Bus. Each PXB provides two independent 32-bit, 33MHz PCI buses, with an option to link the two buses into a single 64-bit,
33MHz bus.
Figure 4.29 shows a typical high-end server block diagram using the 450NX chipset.
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1.2
Cache
1.2
Cache
1.2
Cache
1.2
Cache
Pentium® II
Xeon™
processor
Pentium® II
Xeon™
processor
Pentium® II
Xeon™
processor
Pentium® II
Xeon™
processor
Optional
Cluster
Bridge
System Bus
Expander
Buses
X1
PXB #1
PCI
Expander
Bridge
1B
1A
RCGs
MUXs
MA(13:0)
Control
Memory
Subsystem
1 or 2 cards
X0
PXB #0
PCI
Expander
Bridge
0B
BMIDE HDDs
I/O
APIC
4 PCI Buses
32-bit, 33-MHz, 3.3v or 5v
Can link pairs into 64-bit bus
USB
PIIX4E
South Bridge
0A
PCI
Slots
Figure 4.29
AGTL+ 100 MHz
MD(71:0)
MIOC
Memory
and I/O
Controller
third-party
controls
261
BIOS
Flash
EPROM
IDE CD-ROM
ISA slots
XCVR
KBC
8042
SND
High-end server block diagram using the Intel 440NX chipset.
The 450NX supports one or two memory cards. Each card incorporates an RCG chip and two
MUX chips, in addition to the memory DIMMs. Up to 8GB of memory is supported in total.
The primary features of the 450NX include the following:
■ Slot 2 (SC330) processor bus interface at 100MHz
■ Supports up to four-way processing
■ Support for two dedicated PCI expander bridges (PXBs)
■ Up to four 32-bit PCI buses or two 64-bit PCI buses
The 450NX chipset does not support AGP, because high-end video is not an issue in network file
servers.
Intel 810
Introduced in April of 1999, the Intel 810 chipset (code-named Whitney) represents a major
change in chipset design from the standard North and South Bridges that have been used since
the 486 days. The 810 chipset allows for improvements in system performance, all for less cost
and system complexity.
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The major features of the 810 chipset include
■ 440BX chipset technology foundation
■ 66/100MHz System Bus capability
■ Integrated Intel 3D graphics with Direct AGP for 2D and 3D graphics
■ Efficient use of system memory for graphics performance
■ Optional 4MB of dedicated display cache video memory
■ Digital Video Out port compatible with DVI specification for flat panel displays
■ Software MPEG-2 DVD playback with Hardware Motion Compensation
■ Accelerated Hub Architecture for increased 66MHz I/O performance
■ Supports UDMA-66 for high performance IDE drives
■ Integrated Audio-Codec 97 (AC97) controller
■ Supports low-power sleep modes
■ Random Number Generator (RNG) for stronger security products
■ Integrated USB controller
■ Elimination of ISA Bus
The 810 chipset (see Figure 4.30) consists of three major components:
■ 82810 Graphics Memory Controller Hub (GMCH). 421 Ball Grid Array (BGA) package
■ 82801 Integrated Controller Hub (ICH). 241 Ball Grid Array (BGA) package
■ 82802 Firmware Hub (FWH). In either 32-pin Plastic Leaded Chip Carrier (PLCC) or 40-pin
Thin Small Outline Package (TSOP) packages
Figure 4.30 Intel 810 chipset showing the 82810 (GMCH), 82801 (ICH), and 82802 (FWH) chips.
Photograph used by permission of Intel Corporation.
Compared to the previous North/South Bridge designs, there are some fairly significant changes
in the 810 chipset. The previous system designs had the North Bridge acting as the memory controller, talking to the South Bridge chip via the PCI bus. This new design has the Graphics
Memory Controller Hub (GMCH) taking the place of the North Bridge, which talks to the I/O
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263
Controller Hub (ICH) via a 66MHz dedicated interface called the Accelerated Hub Architecture
(AHA) bus. In particular, implementing a direct connection between the North and South Bridges
in this manner was key in implementing the new UDMA-66 high-speed IDE interface for hard
disks, DVD drives, and other IDE devices.
Figure 4.31 shows a system block diagram for the 810 chipset.
Overall there is still a three-tier system approach as with the previous North/South Bridge and
super I/O chip circuits used in previous motherboard designs. The big difference is that the lowest
speed in this new design is the 33MHz PCI bus. The old 8MHz ISA bus is finally put out to pasture, as there is no direct provision for ISA in this chipset. It is possible to integrate an ISA bridge
chip in an 810 motherboard, so you might yet see some of these boards with ISA slots, but it is
doubtful due to the extra cost and little benefit this would provide.
With the 810 chipset, ISA is finally dead.
CPU
L1
Cache
L1
Cache
Core or
1/2 Core
66/100 MHz
CPU Bus
100 MHz
Direct
AGP
Video
SDRAM
Display
Cache
82810
GMCH
100 MHz
SDRAM
DIMMs
Digital
LCD
Analog
Monitor
66 MHz
Accelerated Hub Architecture (AHA) Bus
USB
AC97
Codec
Speaker
Kybd
82801
ICH
Speaker
CMUS
Clock
L1
Cache
Mouse
Floppy
COM1
LPT1
33 MHz
PCI Slots
82801
FWH
ROM
BIOS
Figure 4.31
Intel 810 Chipset system block diagram.
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The 82810 Graphics Memory Controller Hub (GMCH) uses an internal Direct AGP (integrated
AGP) interface to create 2D and 3D effects and images. The video capability integrated into the
82810 chip features Hardware Motion Compensation to improve software DVD video quality and
both analog and direct digital video out ports, which enable connections to either traditional TVs
(via an external converter module) or the new direct digital flat panel displays. The GMCH chip
also incorporates the System Manageability Bus, which allows networking equipment to monitor
the 810 chipset platform. Using ACPI specifications, the system manageability function enables
low-power sleep mode and conserves energy when the system is idle.
Note that there are two versions of the GMCH, known as the 82810 and 82810-DC100. The latter
DC100 (Display Cache 100MHz) version has the option for up to 4MB of 100MHz SDRAM to
be directly connected as a dedicated display cache. The regular 82810 GMCH chip lacks this provision.
The 82801 I/O Controller Hub (ICH) employs Accelerated Hub Architecture for a direct connection from the GMCH chip. This is twice as fast (266MB/sec) as the previous North/South Bridge
connections that used the PCI bus. Plus, the AHA bus is dedicated, meaning that no other devices
will be on it. The AHA bus also incorporates optimized arbitration rules allowing more functions
to run concurrently, enabling better video and audio performance.
The ICH also integrates dual IDE controllers, which run up to either 33MB/s (UDMA-33 or UltraATA/33) or 66MB/s (UDMA-66 or Ultra-ATA/66). Note that there are two versions of the ICH chip.
The 82801AA (ICH) incorporates the 66MB/s capable IDE and supports up to six PCI slots, while
the 82801AB (ICH0) only supports 33MB/sec maximum and supports up to four PCI slots.
The ICH also integrates an interface to an Audio-Codec 97 (AC97) controller, dual USB ports, and
the PCI bus with up to four or six slots. The Integrated Audio-Codec 97 controller enables software audio and modem by using the processor to run sound and modem software. By reusing
existing system resources, this lowers the system cost by eliminating components.
The 82802 Firmware Hub (FWH) incorporates the system BIOS and video BIOS, eliminating a
redundant nonvolatile memory component. The BIOS within the FWH is flash type memory, so
it can be field updated at any time. In addition, the 82802 contains a hardware Random Number
Generator (RNG). The RNG provides truly random numbers to enable fundamental security
building blocks supporting stronger encryption, digital signing, and security protocols. There are
two versions of the FWH, called the 82802AB and 82802AC respectively. The AB version incorporates 512KB (4Mbit) of flash BIOS memory, and the AC version incorporates a full 1MB (8Mbit) of
BIOS ROM.
With the Intel 810 chipset, Intel has done something that many in the industry were afraid of—
they have integrated the video and graphics controller directly into the motherboard chipset.
This means that systems using the 810 chipset won’t have an AGP slot, and won’t be able to use
conventional AGP video cards. From a performance standpoint, this is not really a problem. The
video they have integrated is an outstanding performer, and it has direct access to the rest of the
chipset at a data rate even faster than standard AGP. The direct AGP interface built-in to the 810
chipset runs at 100MHz, rather than the 66MHz of standard AGP. Intel calls the integrated
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interface Direct AGP, and it describes the direct connection between the memory and processor
controllers with the video controller all within the same chip.
This probably dictates the future of mainstream PCs, which means the video card, as we know it,
will be reserved only for higher end systems. With the 810 chipset, Intel has let it be known in a
big way that they have entered the PC video business. If I were a video chip or board manufacturer, I would be carefully studying my options in other areas for the future!
In fact, the theme with the 810 chipset is one of integration. The integrated video means no
video cards are required; the integrated AC97 interface means that conventional modems and
sound cards are not required. Plus, there is an integrated CMOS/Clock chip (in the ICH), and
even the BIOS is integrated in the FWH chip. All in all the 810 should be taken as a sign for
things to come in the PC industry, which means more integration, better overall performance,
and less cost.
Third-Party (non-Intel) P6 Class Chipsets
Acer Laboratories, Inc. (ALi)
Aladdin Pro II
The Acer Labs (ALi) Aladdin Pro II M1621 is a two-chip set for P6 (Pentium Pro and Pentium II)
processors consisting of two BGA package chips, the 456-pin BGA package M1621 North Bridge,
and either the M1533 or M1543 South Bridge. This is one of the first Slot 1 P6 processor chipsets
from a company other than Intel.
The M1621 North Bridge includes an AGP, memory and I/O controller, and a data path with multiport buffers for data acceleration. It can support multiple Pentium II processors with bus speeds
of 60, 66, and 100MHz. This chipset is equivalent to the 440BX chipset from Intel.
The integrated memory controller supports FPM, EDO, and SDRAM with a total capacity of up to
1GB (SDRAM) or 2GB (EDO). ECC (Error Correcting Code) memory is supported, allowing use in
mission-critical or fileserver applications. Memory timing is x-1-1-1-1-1-1-1 in back-to-back
SDRAM reads, or x-2-2-2-2-2-2-2 in back-to-back EDO reads.
The M1621 supports AGP v1.0, in both 1x and 2x modes, and is fully compliant with PCI Rev.
2.1, allowing for concurrent PCI operations. The M1621 can be used with either the M1533
South Bridge or M1543 South Bridge/Super I/O combo chips.
The M1533 South Bridge includes the following features:
■ PCI-to-ISA Bridge
■ Built-in keyboard/mouse controller
■ Enhanced Power Management, featuring ACPI (Advanced Configuration and Power
Interface)
■ Two-port USB interface
■ Dual channel Ultra-DMA/33 IDE host adapter
■ 328-pin BGA package
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M1543 includes all features in the 1533 plus fully integrated Super I/O, including a Floppy Disk
Controller, two high-speed serial ports, and one multimode parallel port.
VIA Technologies
Apollo P6/97
The VT82C680 Apollo P6 is a high-performance, cost-effective, and energy-efficient chipset for
the implementation of PCI/ISA desktop and notebook personal computer systems based on 64-bit
Intel P6 processors. This was one of the first non-Intel P6 chipsets of any kind available and is
functionally equivalent to the Intel 440FX chipset. The Apollo P6 chipset supports dual processor
configurations with up to 66MHz external CPU bus speed. The DRAM and PCI bus are also independently powered so that each of the buses can be run at 3.3v or 5v. The ISA bus always runs at
5v. The Apollo P6 supports up to 1GB of DRAM. This chipset never really achieved much popularity in the market.
Apollo Pro
The Apollo Pro is a high-performance chipset for Slot 1 mobile and desktop PC systems. The
Apollo Pro includes support for advanced system power management capability for both desktop
and mobile PC applications, PC100 SDRAM, AGP 2x mode, and multiple CPU/DRAM timing configurations. The Apollo Pro chipset is comparable in features to the 440BX and PIIX4e chipset
from Intel, and represents one of the first non-Intel chipsets to support the Socket 1 architecture.
The VIA Apollo Pro consists of two devices—the VT82C691 North Bridge chip and the
VT82C596, a BGA-packaged South Bridge with a full set of mobile, power-management features.
For cost-effective desktop designs, the VT82C691 can also be configured with the VT82C586B
South Bridge.
The VT82C691 Apollo Pro North Bridge supports all Slot-1 (Intel Pentium II) and Socket 8 (Intel
Pentium Pro) processors. The Apollo Pro also supports the 66MHz and the newer 100 MHz CPU
external bus speed required by the 350MHz and faster Pentium II processors. AGP v1.0 and PCI
2.1 are also supported, as are FPM, EDO, and SDRAM. Different DRAM types may be used in
mixed combinations in up to eight banks and up to 1GB of DRAM. EDO memory timing is 5-2-22-2-2-2-2 for back-to-back accesses, and SDRAM timing is 6-1-1-1-2-1-1-1 for back-to-back
accesses.
The VT82C596 South Bridge supports both ACPI (Advanced Configuration and Power Interface)
and APM (Advanced Power Management), and includes an integrated USB Controller and dual
UltraDMA-66 EIDE ports.
Silicon integrated Systems (SiS)
SiS5600/5595
The 5600/5595 chipset was introduced in June 1998, and is designed for low-cost Celeron CPUs
with a 66MHz or 100MHz host bus. SiS intends to use this low-cost chipset to help push the
Pentium II PC technology toward the sub-$1,000 PC market.
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Super I/O Chips
The third major chip seen on most PC motherboards is called the Super I/O chip. This is a chip
that normally integrates devices formerly found on separate expansion cards in older systems.
Most Super I/O chips contain, at a minimum, the following components:
■ Floppy controller
■ Dual serial port controllers
■ Parallel port controller
The floppy controllers on most Super I/O chips will handle two drives, but some of them can
only handle one. Older systems often required a separate floppy controller card.
The dual serial port is another item that was formerly on one or more cards. Most of the better
Super I/O chips implement a buffered serial port design known as a UART (Universal
Asynchronous Receiver Transmitter), one for each port. Most mimic the standalone NS16550A
high-speed UART, which was created by National Semiconductor. By putting the function of two
of these chips into the Super I/O chip, we essentially have these ports built-in to the motherboard.
Virtually all Super I/O chips also include a high-speed multimode parallel port. The better ones
allow three modes, called standard (bidirectional), Enhanced Parallel Port (EPP), and the
Enhanced Capabilities Port (ECP) modes. The ECP mode is the fastest and most powerful, but
selecting it also means your port will use an ISA bus 8-bit DMA channel, usually DMA channel 3.
As long as you account for this and don’t set anything else to that channel (such as a sound card,
and so on), the EPC mode parallel port should work fine. Some of the newer printers and scanners that connect to the system via the parallel port will use ECP mode, which was initially
invented by Hewlett-Packard.
The Super I/O chip may contain other components, as well. For example, currently the most popular Pentium II motherboard on the market—the Intel SE440BX ATX motherboard—uses an SMC
(Standard Microsystems Corp.) FDC37C777 Super I/O chip. This chip incorporates the following
functions:
■ Single floppy drive interface
■ Two high-speed serial ports
■ One ECP/EPP multimode parallel port
■ 8042-style keyboard and mouse controller
Only the keyboard and mouse controller are surprising here; all the other components are in
most Super I/O chips. The integrated keyboard and mouse controller saves the need to have this
chip as a separate part on the board.
One thing I’ve noticed over the years is that the role of the Super I/O chip has decreased more
and more in the newer motherboards. This is primarily due to Intel moving Super I/O functions
such as IDE directly into the chipset South Bridge component, where these devices can attach to
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the PCI bus rather than the ISA bus. One of the shortcomings of the Super I/O chip is that it is
interfaced to the system via the ISA bus, and shares all the speed and performance limitations of
that 8MHz bus. Moving the IDE over to the PCI bus allowed higher speed IDE drives to be developed that could transfer at the faster 33MHz PCI bus speed.
As Intel combines more and more functions into their main chipset, and as USB-based peripherals replace standard serial, parallel, and floppy controller-based devices, you will probably see the
Super I/O chip fade away on some future motherboard designs. At least one of the third-party
chipsets has already combined the South Bridge and Super I/O chip into a single component, saving space and reducing parts count on the motherboard.
Motherboard CMOS RAM Addresses
In the original AT system, a Motorola 146818 chip was used as the RTC (Real-time Clock) and
CMOS (Complementary Metal-Oxide Semiconductor)RAM chip. This is a special chip that had a
simple digital clock, which used 10 bytes of RAM, and an additional 54 more bytes of leftover
RAM in which you could store anything you wanted. The designers of the IBM AT used these
extra 54 bytes to store the system configuration.
Modern PC systems don’t use the Motorola chip; instead, they incorporate the functions of this
chip into the motherboard chipset (South Bridge), Super I/O chip, or they use a special battery
and NVRAM (Non-Volatile RAM) module from companies such as Dallas or Benchmarq.
Table 4.10 shows the standard format of the information stored in the 64-byte standard CMOS
RAM module. This information controls the configuration of the system and is read and written
by the system Setup program.
Table 4.10
AT CMOS RAM Addresses
Offset
Hex
Offset
Dec
Field
Size
Function
00h
0
1 byte
Current second in binary coded decimal (BCD)
01h
1
1 byte
Alarm second in BCD
02h
2
1 byte
Current minute in BCD
03h
3
1 byte
Alarm minute in BCD
04h
4
1 byte
Current hour in BCD
05h
5
1 byte
Alarm hour in BCD
06h
6
1 byte
Current day of week in BCD
07h
7
1 byte
Current day in BCD
08h
8
1 byte
Current month in BCD
09h
9
1 byte
Current year in BCD
0Ah
10
1 byte
Status register A
Bit 7 = Update in progress
0 = Date and time can be read
1 = Time update in progress
Bits 6–4 = Time frequency divider
010 = 32.768khz
Bits 3–0 = Rate selection frequency
0110 = 1.024KHz square wave frequency
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Offset
Hex
Offset
Dec
Field
Size
Function
0Bh
11
1 byte
Status register B
Bit 7 = Clock update cycle
0 = Update normally
1 = Abort update in progress
Bit 6 = Periodic interrupt
0 = Disable interrupt (default)
1 = Enable interrupt
Bit 5 = Alarm interrupt
0 = Disable interrupt (default)
0 = Disable interrupt (default)
1 = Enable interrupt
Bit 4 = Update-ended interrupt
0 = Disable interrupt (default)
1 = Enable interrupt
Bit 3 = Status register A square wave frequency
0 = Disable square wave (default)
1 = Enable square wave
Bit 2 = Date format
0 = Calendar in BCD format (default)
1 = Calendar in binary format
Bit 1 = 24-hour clock
0 = 24-hour mode (default)
1 = 12-hour mode
Bit 0 = Daylight Savings Time
0 = Disable Daylight Savings (default)
1 = Enable Daylight Savings
0Ch
12
1 byte
Status register C
Bit 7 = IRQF flag
Bit 6 = PF
Bit 5 = AF flag
Bit 4 = UF flag
Bits 3–0 = Reserved
0Dh
13
1 byte
Status register D
Bit 7 = Valid CMOS RAM bit
0 = CMOS battery dead
1 = CMOS battery power good
Bits 6–0 = Reserved
0Eh
14
1 byte
Diagnostic status
Bit 7 = Real-time clock power status
0 = CMOS has not lost power
1 = CMOS has lost power
Bit 6 = CMOS checksum status
0 = Checksum is good
1 = Checksum is bad
Bit 5 = POST configuration information status
0 = Configuration information is valid
1 = Configuration information is invalid
Bit 4 = Memory size compare during POST
0 = POST memory equals configuration
1 = POST memory not equal to configuration
Bit 3 = Fixed disk/adapter initialization
0 = Initialization good
1 = Initialization failed
Bit 2 = CMOS time status indicator
0 = Time is valid
1 = Time is Invalid
Bits 1–0 = Reserved
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(continues)
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Continued
Offset
Hex
Offset
Dec
Field
Size
Function
0Fh
15
1 byte
Shutdown code
00h = Power on or soft reset
01h = Memory size pass
02h = Memory test past
03h = Memory test fail
04h = POST end; boot system
05h = JMP double word pointer with EOI
06h = Protected mode tests pass
07h = Protected mode tests fail
07h = Protected mode tests fail
08h = Memory size fail
09h = Int 15h block move
0Ah = JMP double word pointer without EOI
0Bh = used by 80386
10h
16
1 byte
Floppy disk drive types
Bits 7–4 = Drive 0 type
Bits 3–0 = Drive 1 type
0000 = None
0001 = 360KB
0010 = 1.2MB
0011 = 720KB
0100 = 1.44MB
11h
17
1 byte
Reserved
12h
18
1 byte
Hard disk types
Bits 7–4 = Hard disk 0 type (0–15)
Bits 3–0 = Hard disk 1 type (0–15)
13h
19
1 byte
Reserved
14h
20
1 byte
Installed equipment
Bits 7–6 = Number of floppy disk drives
00 = 1 floppy disk drive
01 = 2 floppy disk drives
Bits 5–4 = Primary display
00 = Use display adapter BIOS
01 = CGA 40-column
10 = CGA 80-column
11 = Monochrome Display Adapter
Bits 3–2 = Reserved
Bit 1 = Math coprocessor present
Bit 0 = Floppy disk drive present
15h
21
1 byte
Base memory low-order byte
16h
22
1 byte
Base memory high-order byte
17h
23
1 byte
Extended memory low-order byte
18h
24
1 byte
Extended memory high-order byte
Hard Disk 0 Extended Type (0–255)
19h
25
1 byte
1Ah
26
1 byte
Hard Disk 1 Extended Type (0–255)
1Bh
27
9 bytes
Reserved
2Eh
46
1 byte
CMOS checksum high-order byte
2Fh
47
1 byte
CMOS checksum low-order byte
30h
48
1 byte
Actual extended memory low-order byte
31h
49
1 byte
Actual extended memory high-order byte
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Offset
Hex
Offset
Dec
Field
Size
Function
32h
50
1 byte
Date century in BCD
33h
51
1 byte
POST information flag
Bit 7 = Top 128KB base memory status
0 = Top 128KB base memory not installed
1 = Top 128KB base memory installed
Bit 6 = Setup program flag
0 = Normal (default)
1 = Put out first user message
Bits 5–0 = Reserved
34h
52
2 bytes
Reserved
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271
Note that many newer systems have more than 64 bytes of CMOS RAM; in fact, in some systems
they might have 2KB or 4KB. The extra room is used to store the Plug-and-Play information
detailing the configuration of adapter cards and other options in the system. As such, there is no
100 percent standard for how CMOS information is stored in all systems. Table 4.10 only shows
how the original systems did it; newer BIOS versions and motherboard designs can do things differently. You should consult the BIOS manufacturer for more information if you want the full
details of how CMOS is stored, because the CMOS configuration and Setup program is normally a
part of the BIOS. This is another example of how close the relationship is between the BIOS and
the motherboard hardware.
There are backup programs and utilities in the public domain for CMOS RAM information, which
can be useful for saving and later restoring a configuration. Unfortunately, these programs would
be BIOS specific and would only function on a BIOS they are designed for. As such, I don’t normally rely on these programs because they are too motherboard and BIOS specific and will not
work on all my systems seamlessly.
Table 4.11 shows the values that can be stored by your system BIOS in a special CMOS byte called
the diagnostics status byte. By examining this location with a diagnostics program, you can determine whether your system has set trouble codes, which indicate that a problem previously has
occurred.
Table 4.11
CMOS RAM Diagnostic Status Byte Codes
Bit Number
7 6 5 4 3 2 1 0
Hex
Function
1 • • • • • • •
80
Real-time clock (RTC) chip lost power
• 1 • • • • • •
40
CMOS RAM checksum is bad
• • 1 • • • • •
20
Invalid configuration information found at POST
• • • 1 • • • •
10
Memory size compare error at POST
• • • • 1 • • •
08
Fixed disk or adapter failed initialization
• • • • • 1 • •
04
Real-time clock (RTC) time found invalid
• • • • • • 1 •
02
Adapters do not match configuration
• • • • • • • 1
01
Time-out reading an adapter ID
• • • • • • • •
00
No errors found (Normal)
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If the Diagnostic status byte is any value other than zero, you will normally get a CMOS configuration error on startup. These types of errors can be cleared by rerunning the Setup program.
Motherboard Interface Connectors
There are a variety of different connectors on a modern motherboard. Figure 4.32 shows the location of these connectors on a typical motherboard (using the Intel SE440BX model as the example). Several of these connectors such as power supply connectors, serial and parallel ports, and
keyboard/mouse connectors are covered in other chapters. Tables 4.12–4.16 contain the pinouts
of most of the other different interface and I/O connectors you will find.
◊◊ See “Power Supply Connectors,” p. 1102.
◊◊ See “Serial Ports,” p. 872, and “Parallel Ports,” p. 883.
◊◊ See “Keyboard/Mouse Interface Connectors,” p. 920.
◊◊ See “USB (Universal Serial Bus),” p. 892.
◊◊ See “ATA I/O Connector,” p. 514.
Table 4.12
Infrared Data (IrDA) Pin-Header Connector
Pin
Signal
Pin
Signal
1
+5 V
4
Ground
2
Key
5
IrTX
3
IrRX
6
CONIR (Consumer IR)
Table 4.13
Battery Connector
Pin
Signal
Pin
Signal
1
Gnd
3
KEY
2
Unused
4
+6v
Table 4.14
LED and Keylock Connector
Pin
Signal
Pin
Signal
1
LED Power (+5v)
4
Keyboard Inhibit
2
KEY
5
Gnd
3
Gnd
Table 4.15
Speaker Connector
Pin
Signal
Pin
Signal
1
Ground
3
Board-Mounted Speaker
2
KEY
4
Speaker Output
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A
B
C
D
F
G
H
273
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Super I/O Chips
I
J
E
1
1
1
1
1
1
1
1
6
5
1
2
2
40
2
39
1
11
1
10
20
1
40
1
39
T
S
R
Q P
O
N
34
1 2
1
M
33
L
A
Wake on Ring (J1A1)
K
Fan 1 (J8M1)
B
PCI slots (J4D2, J4D1, J4C1, J4B1)
L
Diskette drive (J8K1)
C
Optional Wake on LAN technology (J1C1)
M
Power supply (J7L1)
D
Fan 3 (J3F2)
N
Optional SCSI LED (J8J1)
E
Optional Auxiliary Line In (J2F2)
O
Front panel (J8G2)
F
Optional telephony (J2F1)
P
Primary and secondary IDE (J7G1, J8G1)
G
Optional CD-ROM audio (J1F1)
Q
DIMMs (J6J1, J6J2, J7J1)
H
Optional chassis intrusion (J3F1)
R
A.G.P. (J4E1)
I
Slot 1 (J4J1)
S
PC/PCI (J6D1)
J
Fan 2 (J4M1)
T
ISA slots (J4B2, J4A1)
Figure 4.32
Typical motherboard connectors (Intel SE440BX shown).
Table 4.16
Microprocessor Fan Power Connector
Pin
Signal Name
1
Ground
2
+12V
3
Sense tachometer
K
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Caution
Do not place a jumper on this connector; serious board damage will result if the 12v is shorted to ground.
Note that some boards have a board mounted piezo speaker. It is enabled by placing a jumper
over pins 3 and 4, which routes the speaker output to the board-mounted speaker. Removing the
jumper allows a conventional speaker to be plugged in.
Some other connectors that you might find on some newer motherboards are listed in Tables
4.17–4.22.
Table 4.17
Chassis Intrusion (Security) Pin-Header
Pin
Signal Name
1
Ground
2
CHS_SEC
Table 4.18
Wake on LAN Pin-Header
Pin
Signal Name
1
+5 VSB
2
Ground
3
WOL
Table 4.19
CD Audio Connector
Pin
Signal Name
1
CD_IN-Left
3
Ground
2
Ground
4
CD_IN-Right
Table 4.20
Pin
Signal Name
Telephony Connector
Pin
Signal Name
1
Audio Out (monaural)
3
Ground
2
Ground
4
Audio In (monaural)
Table 4.21
Pin
Signal Name
ATAPI-Style Line In Connector
Pin
Signal Name
Pin
Signal Name
1
Left Line In
3
Ground
2
Ground
4
Right Line In (monaural)
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Table 4.22
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275
Wake on Ring Pin-Header
Pin
Signal Name
1
Ground
2
RINGA
Intel and several other motherboard manufacturers like to place all the front-panel motherboard
connectors in a single row as shown in Figure 4.33.
27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
* * • * * *
Speaker
Figure 4.33
Reset
• * • * • * * • * • * * * * •*• ** * *
Power LED HD LED Infrared Data
Sleep Power
Typical ATX motherboard front panel connectors (Intel motherboard shown).
Table 4.23 shows the designations for the front-panel motherboard connectors commonly used
on Intel ATX motherboards.
Table 4.23
ATX Motherboard Front Panel Connectors
Connector
Pin
Signal Name
Speaker
27
SPKR_HDR
Reset
26
PIEZO_IN
25
Key
24
Ground
23
SW_RST
22
Ground
none
21
No connect/Key
Sleep/Power LED
20
PWR_LED
19
Key
18
Ground
none
17
No connect/Key
Hard Drive LED
16
HD_PWR
15
HD Active#
14
Key
13
HD_PWR +5 V
none
12
No connect
IrDA
11
CONIR (Consumer IR)
10
IrTX
9
Ground
8
IrRX
7
Key
6
+5V
(continues)
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Table 4.23
Continued
Connector
Pin
Signal Name
none
5
No connect
Sleep/Resume
Power On
4
SLEEP_PU (pullup)
3
SLEEP
2
Ground
1
SW_ON#
System Bus Functions and Features
At the heart of every motherboard are the buses that make it up. A bus is a common pathway
across which data can travel within a computer. This pathway is used for communication and
can be established between two or more computer elements.
The PC has a hierarchy of different buses. Most modern PCs have at least three different buses;
some have four or more. They are hierarchical because each slower bus is connected to the faster
one above it. Each device in the system is connected to one of the buses, and some devices (primarily the chipset) act as bridges between the various buses.
The main buses in a modern system are as follows:
■ The Processor Bus. This is the highest-speed bus in the system and is at the core of the
chipset and motherboard. This bus is used primarily by the processor to pass information
to and from cache or main memory and the North Bridge of the chipset. The processor bus
in Pentium II systems runs at either 66 or 100MHz and has the full 64-bit data path width
of the processor.
■ The AGP (Accelerated Graphics Port) Bus. This is a high-speed 66MHz, 32-bit bus specifically
for a video card. It is connected to the North Bridge of the chipset and is manifested as a
single AGP slot in systems that support it.
■ The PCI (Peripheral Component Interconnect) Bus. This is a 33Mhz, 32-bit bus found in virtually all newer 486 systems and Pentium and higher processor systems. This bus is generated
by the chipset North Bridge, which acts as the PCI controller. This bus is manifested in the
system as a collection of 32-bit slots, normally about four on most motherboards. Highspeed peripherals such as SCSI adapters, network cards, video cards, and more can be
plugged in to PCI bus slots. The chipset South Bridge is plugged in to the PCI bus, and
from there generates the IDE and USB ports.
■ The ISA (Industry Standard Architecture) Bus. This is an 8MHz, 16-bit bus that remains in systems today after first appearing in the original PC in 8-bit, 5MHz form, and in the 1984
IBM AT in full 16-bit form. It is a very slow-speed bus, but is still ideal for certain slowspeed or older peripherals. The PC industry has been loath to give up this bus, despite pressure from Microsoft and Intel to do away with it in future PC designs. Most people have
used it in recent times for plug-in modems, sound cards, and various other low-speed
peripherals. The ISA bus is generated by the South Bridge part of the motherboard chipset,
which acts as the ISA bus controller and the interface between the ISA bus and the faster
PCI bus above it. The motherboard’s Super I/O chip is normally connected to this bus.
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The system chipset is the conductor that controls the orchestra of system components, allowing
each to have their turn on their respective buses.
Bus Type
Width
(bits)
Speed
(MHz)
Bandwidth
(MB/sec)
8-bit ISA
8
4.77
2.39
16-bit ISA
16
8.33
8.33
EISA*
32
8.33
33.3
VLB*
32
33.33
133.33
PCI
32
33.33
133.33
PCI-2x**
32
66.66
266.66
PCI 64-bit**
64
33.33
266.66
PCI-2x 64-bit**
64
66.66
533.33
AGP
32
66.66
266.66
AGP-2x
32
66.66
533.33
AGP-4x*
32
66.66
1,066.66
* EISA and VLB are no longer used in current motherboard designs.
** Note that these bus types are proposed and have not yet been implemented in PC systems.
The PCI bus has two proposed extensions. One is to go from 32 bits to 64 bits. The other is to
double the clock speed of the bus to 66MHz. So far, neither of these has been implemented in PC
systems, and it doesn’t seem likely they will in the near future. More likely we will see improvements in other areas such as AGP, which has already moved to 2x mode and will move to a 4x
mode in the future.
Interestingly enough, these faster modes will be achieved at the same clock rate; the only difference is that 2 or 4 bits will be transferred for every hertz (cycle) rather than the 1 bit per cycle
standard today. This will allow the AGP bus to keep pace with future video needs, all the way to
over 1,066MB/sec!
The following sections discuss the processor and other subset buses in the system, and the main
I/O buses mentioned in the previous table.
The Processor Bus
The processor bus is the communication pathway between the CPU and motherboard chipset,
more specifically the North Bridge. This bus runs at the full motherboard speed—normally
66MHz, 75MHz, or 100MHz—and is used to transfer data between the CPU and the chipset
North Bridge. It also transfers data between the CPU and an external memory cache on Pentium
(P5 class) systems. Figure 4.19 shows how this bus fits into a typical Pentium (P5 class) PC
system.
Later in this chapter, Figure 4.34 shows where and how the other main buses, such as the PCI
and IDE buses, fit into the system. As you can see, there is clearly a three-tier architecture with
the fastest CPU bus on top, the PCI bus next, and the ISA bus at the bottom. Different components in the system are connected to one of these three main buses.
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Pentium (P5) class systems have an external cache for the CPU; these caches are connected to the
processor bus that runs at the motherboard speed (normally 66MHz). Thus, as the Pentium
processors have been getting faster and faster, the L2 cache has unfortunately remained at the relatively slow motherboard speed. This was solved in the Pentium Pro and Pentium II systems.
They have moved the L2 cache off of the motherboard and directly onto the CPU. By incorporating the L2 cache in the CPU, they can run it at a speed closer to the true CPU speed. In the
Pentium Pro, the L2 cache actually does run at full CPU speed, but in the Pentium II it runs at
one half of the processor speed. This is still much faster than the motherboard-bound cache on
the Socket 7 P5 class systems. The built-in L2 CPU cache is one of the main reasons the Socket 8
and Slot 1 architecture is superior to the Socket 7 designs.
Pentium
CPU
Up to 266MHz
L1
Cache
Processor Bus
66MHz
L2
Cache
(15ns)
66MHz
16/66MHz
North
Bridge
(430TX)
PCI Bus 33MHz
USB1
EDO SIMM (16MHz)
or
SDRAM DIMM (66MHz)
PCI
Slots
USB2
South
Bridge
(PIIX4)
CMOS
&
RTC
IDE 1
PCI
Video
IDE 2
ISA Bus 8 MHz
ISA
Slots
Floppy
Keyboard Mouse
Super
I/O
(87307)
COM 1
COM 2
LPT 1
ROM
Flash BIOS
Figure 4.34
system.
Typical Pentium (P5 Class) system architecture showing the different bus levels in the
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Note that recently there is a new version of the Socket 7 architecture called Super-7. It is designed
primarily by AMD and Cyrix for their new Socket 7 P5 class processors that run at motherboard
speeds up to 100MHz. This is definitely better than 66MHz, but still not quite up to the Slot-1
architecture where the L2 cache automatically scales up in speed along with the processor. By
moving the L2 cache off the motherboard, the Slot 1 designs offer greater performance.
Figure 4.35 shows the typical Pentium III system design. You can see the two main changes: One
is that the L2 cache now runs at half processor core speed rather than motherboard speed. Also
note that the motherboard speed has been increased to 100MHz, which dramatically improves
main memory performance combined with 100MHz SDRAM memory. The other main change is
the addition of a new single slot bus called AGP (Accelerated Graphics Port). This allows the
video card to be on its own dedicated high-speed bus, which runs at twice the speed of PCI.
Actually, the speed is misleading, as AGP has 2x and 4x modes that allow a further doubling or
quadrupling of the speed over the base of 66MHz. This results in incredible video bandwidth,
which is necessary for full-motion video capture and display.
Because the purpose of the processor bus is to get information to and from the CPU at the fastest
possible speed, this bus operates at a much faster rate than any other bus in your system; no bottleneck exists here. The bus consists of electrical circuits for data, addresses (the address bus,
which is discussed in the following section), and control purposes. In a Pentium-based system,
the processor bus has 64 data lines, 32 address lines, and associated control lines. The Pentium
Pro and Pentium II have 36 address lines, but otherwise are the same as the Pentium and
Pentium MMX.
The processor bus operates at the same base clock rate as the CPU does externally. This can be
misleading because most CPUs these days run internally at a higher clock rate than they do externally. For example, a Pentium 266 system has a Pentium CPU running at 266MHz internally, but
only 66.6MHz externally, while a Pentium II 450 runs at 450MHz internally but only 100MHz
externally. A Pentium 133, 166, 200, and even a Pentium 233 also run the processor external bus
at 66.6MHz. In most newer systems, the actual processor speed is some multiple (1.5x, 2x, 2.5x,
3x, and so on) of the processor bus.
√√ See “Processor Speed Ratings,” p. 42.
The processor bus is tied to the external processor pin connections and can transfer one bit of
data per data line every one or two clock cycles. Thus, a Pentium, Pentium Pro, or Pentium II can
transfer 64 bits of data at a time.
To determine the transfer rate for the processor bus, you multiply the data width (64 bits for a
Pentium, Pentium Pro, or Pentium II) by the clock speed of the bus (the same as the base or
unmultiplied clock speed of the CPU). If you are using a Pentium, Pentium MMX, Pentium Pro,
or Pentium II chip that runs at a 66MHz motherboard speed, and it can transfer a bit of data each
clock cycle on each data line, you have a maximum instantaneous transfer rate of roughly
528MB/sec. You get this result by using the following formula:
66MHz×64 bits = 4,224Mbit/sec
4,224Mbit/sec÷8 = 528MB/sec
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Up to 550MHz
Pentium
III
L2
Cache
1/2
CPU = 275MHz
L1
Cache
Processor Bus
100MHz
66MHz
100MHz
AGP
North
Bridge
(440BX)
Video
PCI Bus 33 MHz
USB1
100MHz
SDRAM
DIMM
PCI
Slots
USB2
South
Bridge
(PIIX4E)
CMOS
&
RTC
IDE 1
IDE 2
ISA Bus 8MHz
ISA
Slots
Floppy
Keyboard Mouse
Super
I/O
(376777)
COM 1
COM 2
LPT 1
ROM
Flash BIOS
Figure 4.35
Typical Pentium III system architecture showing the different bus levels in the system.
This transfer rate, often called the bandwidth of the bus, represents a maximum. Like all maximums, this rate does not represent the normal operating bandwidth; you should expect much
lower average throughput. Other limiting factors such as chipset design, memory design and
speed, and so on conspire to lower the effective average throughput.
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The Memory Bus
The memory bus is used to transfer information between the CPU and main memory—the RAM
in your system. This bus is connected to the motherboard chipset North Bridge chip. Depending
on the type of memory your chipset (and therefore motherboard) is designed to handle, the
North Bridge will run the memory bus at different speeds. Systems that use FPM (Fast Page Mode)
or EDO (Extended Data Out) memory with a 60ns access time run the memory bus at only
16MHz. That is because 16MHz results in about 60ns cycling speed. Newer chipsets and motherboards that support SDRAM can run the memory bus at 66MHz (15ns) or up to 100MHz (10ns).
This obviously results in faster memory performance and virtually negates the need for having
cache memory on the motherboard. That is why the Pentium II processor was designed to
include a higher speed L2 cache built in, as the SDRAM memory on the motherboard already
runs at the same speed as the motherboard cache found in older Pentium systems. Figure 4.32
and Figure 4.33 show how the memory bus fits into your PC.
Note
Notice that the main memory bus is always the same width as the processor bus. This will define the size of what
is called a “bank” of memory. Memory banks and their width relative to processor buses are discussed in the
“Memory Banks” section in Chapter 6.
The Need for Expansion Slots
The I/O bus or expansion slots are what enables your CPU to communicate with peripheral
devices. The bus and its associated expansion slots are needed because basic systems cannot possibly satisfy all the needs of all the people who buy them. The I/O bus enables you to add devices
to your computer to expand its capabilities. The most basic computer components, such as sound
cards and video cards, can be plugged into expansion slots; you also can plug in more specialized
devices, such as network interface cards, SCSI host adapters, and others.
Note
In most modern PC systems, a variety of basic peripheral devices are built into the motherboard. Most systems
today have at least dual (primary and secondary) IDE interfaces, dual USB (Universal Serial Bus) ports, a floppy
controller, two serial ports, a parallel port, keyboard, and mouse controller built directly into the motherboard.
These devices are normally distributed between the motherboard chipset South Bridge and the Super I/O chip.
(Super I/O chips are discussed earlier in this chapter.)
Many will even add more items such as a built-in sound card, video adapter, SCSI host adapter, or network interface also built into the motherboard. Those items are not built into the motherboard chipset or Super I/O chip, but
would be configured as additional chips installed on the board. Nevertheless, these built-in controllers and ports
still use the I/O bus to communicate with the CPU. In essence, even though they are built in, they act as if there
are cards plugged into the system’s bus slots, including using system resources in the same manner.
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Types of I/O Buses
Since the introduction of the first PC, many I/O buses have been introduced. The reason is simple: Faster I/O speeds are necessary for better system performance. This need for higher performance involves three main areas:
■ Faster CPUs
■ Increasing software demands
■ Greater multimedia requirements
Each of these areas requires the I/O bus to be as fast as possible. Surprisingly, virtually all PC systems shipped today still incorporate the same basic bus architecture as the 1984 vintage IBM
PC/AT. However, most of these systems now also include a second high-speed local I/O bus such
as VL-Bus or PCI, which offer much greater performance for adapters that need it. Many of the
newest systems also include a third high-speed bus called AGP for improved video performance
beyond what PCI offers.
One of the primary reasons why new I/O-bus structures have been slow in coming is compatibility—that old catch-22 that anchors much of the PC industry to the past. One of the hallmarks of
the PC’s success is its standardization. This standardization spawned thousands of third-party I/O
cards, each originally built for the early bus specifications of the PC. If a new high-performance
bus system was introduced, it often had to be compatible with the older bus systems so that the
older I/O cards would not be obsolete. Therefore, bus technologies seem to evolve rather than
make quantum leaps forward.
You can identify different types of I/O buses by their architecture. The main types of I/O architecture are
■ ISA
■ Micro Channel Architecture (MCA)
■ EISA
■ VESA Local Bus (VL-Bus)
■ PCI Local Bus
■ AGP
■ PC-Card (formerly PCMCIA)
■ FireWire (IEEE-1394)
■ Universal Serial Bus (USB)
◊◊ See “PC Cards” pg. 1236.
◊◊ See “IEEE 1394 (Also called i.link or FireWire)” pg. 896.
◊◊ See “USB (Universal Serial Bus)” pg. 892.
The differences among these buses consist primarily of the amount of data that they can transfer
at one time and the speed at which they can do it. Each bus architecture is implemented by a
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chipset that is connected to the processor bus. Typically, this chipset also controls the memory
bus (refer to Figure 4.18 earlier in this chapter). The following sections describe the different
types of PC buses.
The ISA Bus
ISA, which is an acronym for Industry Standard Architecture, is the bus architecture that was introduced as an 8-bit bus with the original IBM PC in 1981; it was later expanded to 16 bits with the
IBM PC/AT in 1984. ISA is the basis of the modern personal computer and the primary architecture used in the vast majority of PC systems on the market today. It may seem amazing that such
a presumably antiquated architecture is used in today’s high-performance systems, but this is true
for reasons of reliability, affordability, and compatibility, plus this old bus is still faster than many
of the peripherals that we connect to it!
Two versions of the ISA bus exist, based on the number of data bits that can be transferred on the
bus at a time. The older version is an 8-bit bus; the newer version is a 16-bit bus. The original 8bit version ran at 4.77MHz in the PC and XT. The 16-bit version used in the AT ran at 6MHz, and
then 8MHz. Later, the industry as a whole agreed on an 8.33MHz maximum standard speed for
8/16-bit versions of the ISA bus for backward compatibility. Some systems have the capability to
run the ISA bus faster than this, but some adapter cards will not function properly at higher
speeds. ISA data transfers require anywhere from two to eight cycles. Therefore, the theoretical
maximum data rate of the ISA bus is about 8MB/sec, as the following formula shows:
8MHz×16 bits = 128Mbit/sec
128Mbit/sec÷2 cycles = 64Mbit/sec
64Mbit/sec÷8 = 8MB/sec
The bandwidth of the 8-bit bus would be half this figure (4MB/sec). Remember, however, that
these figures are theoretical maximums; because of I/O bus protocols, the effective bandwidth is
much lower—typically by almost half. Even so, at 8MB/sec, the ISA bus is still faster than many
of the peripherals we connect to it.
The 8-Bit ISA Bus
This bus architecture is used in the original IBM PC computers. Although virtually nonexistent in
new systems today, this architecture still exists in hundreds of thousands of PC systems in the
field.
Physically, the 8-bit ISA expansion slot resembles the tongue-and-groove system that furniture
makers once used to hold two pieces of wood together. It is specifically called a card/edge
connector. An adapter card with 62 contacts on its bottom edge plugs into a slot on the motherboard that has 62 matching contacts. Electronically, this slot provides eight data lines and 20
addressing lines, enabling the slot to handle 1MB of memory.
Figure 4.36 describes the pinouts for the 8-bit ISA bus.
Figure 4.37 shows how these pins are oriented in the expansion slot.
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Signal
Ground
RESET DRV
+5 Vdc
IRQ 2
-5 Vdc
DRQ 2
-12 Vdc
-CARD SLCTD
+12 Vdc
Ground
-SMEMW
-SMEMR
-IOW
-IOR
-DACK 3
DRQ 3
-DACK 1
DRQ 1
-Refresh
CLK(4.77MHz)
IRQ 7
IRQ 6
IRQ 5
IRQ 4
IRQ 3
-DACK 2
T/C
BALE
+5 Vdc
OSC(14.3MHz)
Ground
Figure 4.36
Pin
Pin
Signal
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
B20
B21
B22
B23
B24
B25
B26
B27
B28
B29
B30
B31
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23
A24
A25
A26
A27
A28
A29
A30
A31
-I/O CH CHK
Data Bit 7
Data Bit 6
Data Bit 5
Data Bit 4
Data Bit 3
Data Bit 2
Data Bit 1
Data Bit 0
-I/O CH RDY
AEN
Address 19
Address 18
Address 17
Address 16
Address 15
Address 14
Address 13
Address 12
Address 11
Address 10
Address 9
Address 8
Address 7
Address 6
Address 5
Address 4
Address 3
Address 2
Address 1
Address 0
Pinouts for the 8-bit ISA bus.
B1
A1
B31 A31
Figure 4.37
Rear
of the
Computer
The 8-bit ISA bus connector.
Although the design of the bus is simple, IBM waited until 1987 to publish full specifications for
the timings of the data and address lines, so in the early days of PC compatibles, manufacturers
had to do their best to figure out how to make adapter boards. This problem was solved, however, as PC-compatible personal computers became more widely accepted as the industry standard and manufacturers had more time and incentive to build adapter boards that worked
correctly with the bus.
The dimensions of 8-bit ISA adapter cards are as follows:
4.2 inches (106.68mm) high
13.13 inches (333.5mm) long
0.5 inch (12.7mm) wide
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The 16-Bit ISA Bus
IBM threw a bombshell on the PC world when it introduced the AT with the 286 processor in
1984. This processor had a 16-bit data bus, which meant that communications between the
processor and the motherboard as well as memory would now be 16 bits wide instead of only 8.
Although this processor could have been installed on a motherboard with only an 8-bit I/O bus,
that would have meant a huge sacrifice in the performance of any adapter cards or other devices
installed on the bus.
The introduction of the 286 chip posed a problem for IBM in relation to its next generation of
PCs: Should the company create a new I/O bus and associated expansion slots to try to come up
with a system that could support both 8- and 16-bit cards? IBM opted for the latter solution, and
the PC/AT was introduced with a set of expansion slots with 16-bit extension connectors. You
can plug an 8-bit card into the forward part of the slot or a 16-bit card into both parts of the slot.
Note
The expansion slots for the 16-bit ISA bus also introduced access keys to the PC environment. An access key is a
cutout or notch in an adapter card that fits over a corresponding tab in the connector into which the adapter card
is inserted. Access keys typically are used to keep adapter cards from being inserted into a connector improperly.
The extension connector in each 16-bit expansion slot adds 36 connector pins to carry the extra
signals necessary to implement the wider data path. In addition, two of the pins in the 8-bit portion of the connector were changed. These two minor changes do not alter the function of 8-bit
cards.
Figure 4.38 describes the pinouts for the full 16-bit ISA expansion slot.
Figure 4.39 shows the orientation and relation of 8-bit and 16-bit ISA bus slots.
The extended 16-bit slots physically interfere with some 8-bit adapter cards that have a skirt—an
extended area of the card that drops down toward the motherboard just after the connector. To
handle these cards, IBM left two expansion ports in the PC/AT without the 16-bit extensions.
These slots, which are identical to the expansion slots in earlier systems, can handle any skirted
PC or XT expansion card. This is not a problem today, as no skirted 8-bit cards have been manufactured for years.
Note
Sixteen-bit ISA expansion slots were introduced in 1984. Since then, virtually every manufacturer of 8-bit expansion
cards has designed them without drop-down skirts so that they fit properly in 16-bit slots. Most new systems do not
have any 8-bit only slots, because a properly designed 8-bit card will work in any 16-bit slot.
Note that some poorly designed motherboards or adapter cards may have fitment problems. It is not uncommon to
find that a full-length card will not work in a particular slot due to interference with the processor heat sink, SIMM
or DIMM memory, voltage regulators, or other components on the board. Systems using the LPX motherboard and
even the Baby-AT motherboard form factors are especially prone to these types of problems. This is another reason
I recommend ATX form factor systems—things fit so much better.
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Signal
Figure 4.38
Pin
Ground
RESET DRV
+5 Vdc
IRQ 9
-5 Vdc
DRQ 2
-12 Vdc
-0 WAIT
+12 Vdc
Ground
-SMEMW
-SMEMR
-IOW
-IOR
-DACK 3
DRQ 3
-DACK 1
DRQ 1
-Refresh
CLK(8.33MHz)
IRQ 7
IRQ 6
IRQ 5
IRQ 4
IRQ 3
-DACK 2
T/C
BALE
+5 Vdc
OSC(14.3MHz)
Ground
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
B20
B21
B22
B23
B24
B25
B26
B27
B28
B29
B30
B31
-MEM CS16
-I/O CS16
IRQ 10
IRQ 11
IRQ 12
IRQ 15
IRQ 14
-DACK 0
DRQ 0
-DACK 5
DRQ5
-DACK 6
DRQ 6
-DACK 7
DRQ 7
+5 Vdc
-Master
Ground
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
D16
D17
D18
Pin
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23
A24
A25
A26
A27
A28
A29
A30
A31
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
Signal
-I/O CH CHK
Data Bit 7
Data Bit 6
Data Bit 5
Data Bit 4
Data Bit 3
Data Bit 2
Data Bit 1
Data Bit 0
-I/O CH RDY
AEN
Address 19
Address 18
Address 17
Address 16
Address 15
Address 14
Address 13
Address 12
Address 11
Address 10
Address 9
Address 8
Address 7
Address 6
Address 5
Address 4
Address 3
Address 2
Address 1
Address 0
-SBHE
Latch Address 23
Latch Address 22
Latch Address 21
Latch Address 20
Latch Address 19
Latch Address 18
Latch Address 17
-MEMR
-MEMW
Data Bit 8
Data Bit 9
Data Bit 10
Data Bit 11
Data Bit 12
Data Bit 13
Data Bit 14
Data Bit 15
Pinouts for the 16-bit ISA bus.
The dimensions of a typical AT expansion board are as follows:
4.8 inches (121.92mm) high
13.13 inches (333.5mm) long
0.5 inch (12.7mm) wide
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8/16-bit ISA Bus Pinouts.
8-bit PC/XT Connector:
Signal
GROUND
RESET DRV
+5 Vdc
IRQ 2
-5 Vdc
DRQ 2
-12 Vdc
-CARD SLCT
+12 Vdc
GROUND
-SMEMW
-SMEMR
-IOW
-IOR
-DACK 3
DRQ 3
-DACK 1
DRQ 1
-REFRESH
CLK (4.77MHz)
IRQ 7
IRQ 6
IRQ 5
IRQ 4
IRQ 3
-DACK 2
T/C
BALE
+5 Vdc
OSC (14.3MHz)
GROUND
Figure 4.39
16-bit AT Connector:
Pin Numbers
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
B20
B21
B22
B23
B24
B25
B26
B27
B28
B29
B30
B31
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23
A24
A25
A26
A27
A28
A29
A30
A31
Signal
-I/O CHK
DATA 7
DATA 6
DATA 5
DATA 4
DATA 3
DATA 2
DATA 1
DATA 0
-I/O RDY
AEN
ADDR 19
ADDR 18
ADDR 17
ADDR 16
ADDR 15
ADDR 14
ADDR 13
ADDR 12
ADDR 11
ADDR 10
ADDR 9
ADDR 8
ADDR 7
ADDR 6
ADDR 5
ADDR 4
ADDR 3
ADDR 2
ADDR 1
ADDR 0
Signal
Pin Numbers
Signal
GROUND
RESET DRV
+5 Vdc
IRQ 9
-5 Vdc
DRQ 2
-12 Vdc
-OWS
+12 Vdc
GROUND
-SMEMW
-SMEMR
-IOW
-IOR
-DACK 3
DRQ 3
-DACK 1
DRQ 1
-REFRESH
CLK (8.33MHz)
IRQ 7
IRQ 6
IRQ 5
IRQ 4
IRQ 3
-DACK 2
T/C
BALE
+5 Vdc
OSC (14.3MHz)
GROUND
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
B20
B21
B22
B23
B24
B25
B26
B27
B28
B29
B30
B31
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23
A24
A25
A26
A27
A28
A29
A30
A31
-I/O CHK
DATA 7
DATA 6
DATA 5
DATA 4
DATA 3
DATA 2
DATA 1
DATA 0
-I/O RDY
AEN
ADDR 19
ADDR 18
ADDR 17
ADDR 16
ADDR 15
ADDR 14
ADDR 13
ADDR 12
ADDR 11
ADDR 10
ADDR 9
ADDR 8
ADDR 7
ADDR 6
ADDR 5
ADDR 4
ADDR 3
ADDR 2
ADDR 1
ADDR 0
-MEM CS16
-I/O CS16
IRQ 10
IRQ 11
IRQ 12
IRQ 15
IRQ 14
-DACK 0
DRQ 0
-DACK 5
DRQ 5
-DACK 6
DRQ 6
-DACK 7
DRQ 7
+5 Vdc
-MASTER
GROUND
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
D16
D17
D18
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
-SBHE
LADDR 23
LADDR 22
LADDR 21
LADDR 20
LADDR 19
LADDR 18
LADDR 17
-MEMR
-MEMW
DATA 8
DATA 9
DATA 10
DATA 11
DATA 12
DATA 13
DATA 14
DATA 15
The 8-bit and 16-bit ISA bus connectors.
Two heights actually are available for cards that are commonly used in AT systems: 4.8 inches
and 4.2 inches (the height of older PC-XT cards). The shorter cards became an issue when IBM
introduced the XT Model 286. Because this model has an AT motherboard in an XT case, it needs
AT-type boards with the 4.2-inch maximum height. Most board makers trimmed the height of
their boards; many manufacturers now make only 4.2-inch tall (or less) boards so that they will
work in systems with either profile.
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32-Bit Buses
After 32-bit CPUs became available, it was some time before 32-bit bus standards became available. Before MCA and EISA specs were released, some vendors began creating their own proprietary 32-bit buses, which were extensions of the ISA bus. Although the proprietary buses were few
and far between, they do still exist.
The expanded portions of the bus typically are used for proprietary memory expansion or video
cards. Because the systems are proprietary (meaning that they are nonstandard), pinouts and
specifications are not available.
The Micro Channel Bus
The introduction of 32-bit chips meant that the ISA bus could not handle the power of another
new generation of CPUs. The 386DX chips can transfer 32 bits of data at a time, but the ISA bus
can handle a maximum 16 bits. Rather than extend the ISA bus again, IBM decided to build a
new bus; the result was the MCA bus. MCA (an acronym for Micro Channel Architecture) is completely different from the ISA bus and is technically superior in every way.
IBM not only wanted to replace the old ISA standard, but also to receive royalties on it; the company required vendors that licensed the new MCA bus to pay IBM royalties for using the ISA bus
in all previous systems. This requirement led to the development of the competing EISA bus (see
the next section on the EISA bus) and hindered acceptance of the MCA bus. Another reason why
MCA has not been adopted universally for systems with 32-bit slots is that adapter cards designed
for ISA systems do not work in MCA systems.
Note
The MCA bus is not compatible with the older ISA bus, so cards designed for the ISA bus do not work in an MCA
system.
MCA runs asynchronously with the main processor, meaning that fewer possibilities exist for timing problems among adapter cards plugged into the bus.
MCA systems produced a new level of ease of use, as anyone who has set up one of these systems
can tell you. An MCA system has no jumpers and switches—neither on the motherboard nor on
any expansion adapter. You don’t need an electrical engineering degree to plug a card into a PC.
What you do need is the Reference disk, which goes with the particular system, and the Options
disks, which go with each of the cards installed in the system. Once a card is installed, you can
load the Options disks files onto the Reference disk; after that, you don’t need the Options disks
anymore. The Reference disk contains the special BIOS and system setup program needed for an
MCA system, and the system cannot be configured without it. IBM maintains a library of all of
their Reference and Options disks at ftp://ftp.pc.ibm.com/pub/pccbbs. Check this site if you
need any of these files.
The MCA bus also supports bus mastering. Through implementing bus mastering, the MCA bus
provides significant performance improvements over the older ISA buses. (Bus mastering is also
implemented in the EISA bus. General information related to bus mastering is discussed in the
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“Bus Mastering” section later in this chapter.) In the MCA bus mastering implementation, any
bus mastering devices can request unobstructed use of the bus in order to communicate with
another device on the bus. The request is made through a device known as the Central Arbitration
Control Point (CACP). This device arbitrates the competition for the bus, making sure all devices
have access and that no single device monopolizes the bus.
Each device is given a priority code to ensure that order is preserved within the system. The main
CPU is given the lowest priority code. Memory refresh has the highest priority, followed by the
DMA channels, and then the bus masters installed in the I/O slots. One exception to this is when
an NMI (non-maskable interrupt) occurs. In this instance, control returns to the CPU immediately.
The MCA specification provides for four adapter sizes, which are described in Table 4.24.
Table 4.24
Physical Sizes of MCA Adapter Cards
Adapter Type
Height
(in Inches)
Length
(in Inches)
Type 3
3.475
12.3
Type 3 half
3.475
6.35
Type 5
4.825
13.1
Type 9
9.0
13.1
Four types of slots are involved in the MCA design:
■ 16-bit
■ 16-bit with video extensions
■ 16-bit with memory-matched extensions
■ 32-bit
IBM still has all the technical reference manuals for MCA available; however, development has
stopped for MCA devices because other faster and more feature-rich buses are available today.
The EISA Bus
EISA is an acronym for Extended Industry Standard Architecture. This standard was announced in
September 1988 as a response to IBM’s introduction of the MCA bus—more specifically, to the
way that IBM wanted to handle licensing of the MCA bus. Vendors did not feel obligated to pay
retroactive royalties on the ISA bus, so they turned their backs on IBM and created their own
buses.
The EISA standard was developed primarily by Compaq, and was intended as being their way of
taking over future development of the PC bus away from IBM. Compaq knew that nobody would
clone their bus if they were the only company that had it, so they essentially gave the design
away to other leading manufacturers. They formed the EISA committee, a non-profit organization
designed specifically to control development of the EISA bus. Very few EISA adapters were ever
developed. Those that were developed centered mainly around disk array controllers and server
type network cards.
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The EISA bus provides 32-bit slots for use with 386DX or higher systems. The EISA slot enables
manufacturers to design adapter cards that have many of the capabilities of MCA adapters, but
the bus also supports adapter cards created for the older ISA standard. EISA provides markedly
faster hard drive throughput when used with devices such as SCSI bus-mastering hard drive controllers. Compared with 16-bit ISA system architecture, EISA permits greater system expansion
with fewer adapter conflicts.
The EISA bus adds 90 new connections (55 new signals) without increasing the physical connector size of the 16-bit ISA bus. At first glance, the 32-bit EISA slot looks a lot like the 16-bit ISA
slot. The EISA adapter, however, has two rows of connectors. The first row is the same kind used
in 16-bit ISA cards; the other, thinner row extends from the 16-bit connectors. This means that
ISA cards can still be used in EISA bus slots. Although this compatibility was not enough to
ensure the popularity of EISA buses, it is a feature that was carried over into the newer VL-Bus
standard. The physical specifications of an EISA card are as follows:
■ 5 inches (127mm) high
■ 13.13 inches (333.5mm) long
■ 0.5 inches (12.7mm) wide
The EISA bus can handle up to 32 bits of data at an 8.33MHz cycle rate. Most data transfers
require a minimum of two cycles, although faster cycle rates are possible if an adapter card provides tight timing specifications. The maximum bandwidth on the bus is 33MB/sec, as the following formula shows:
■ 8.33MHz×32 bits = 266.56Mbit/sec
■ 266.56Mbit/sec÷8 = 33.32MB/sec
Data transfers through an 8- or 16-bit expansion card across the bus would be reduced appropriately. Remember, however, that these figures represent theoretical maximums. Wait states, interrupts, and other protocol factors can reduce the effective bandwidth—typically, by half.
Figure 4.40 describes the pinouts for the EISA bus.
Figure 4.41 shows the locations of the pins.
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B
1
Lower Signal
Ground
+5 Vdc
+5 Vdc
Reserved
Reserved
KEY
Reserved
Reserved
+12 Vdc
M-IO
-LOCK
Reserved
Ground
Reserved
-BE 3
KEY
-BE 2
-BE 0
Ground
+5 Vdc
Latch Address 29
Ground
Latch Address 26
Latch Address 24
KEY
Latch Address 16
Latch Address 14
+5 Vdc
+5 Vdc
Ground
Latch Address 10
Upper Signal
Ground
RESET DRV
+5 Vdc
IRQ 9
-5 Vdc
DRQ 2
-12 Vdc
-0 WAIT
+12 Vdc
Ground
-SMEMW
-SMEMR
-IOW
-IOR
-DACK 3
DRQ 3
-DACK 1
DRQ 1
-Refresh
CLK(8.33MHz)
IRQ 7
IRQ 6
IRQ 5
IRQ 4
IRQ 3
-DACK 2
T/C
BALE
+5 Vdc
OSC(14.3MHz)
Ground
Pin
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
B20
B21
B22
B23
B24
B25
B26
B27
B28
B29
B30
B31
Pin
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23
A24
A25
A26
A27
A28
A29
A30
A31
Upper Signal
-I/O CH CHK
Data Bit 7
Data Bit 6
Data Bit 5
Data Bit 4
Data Bit 3
Data Bit 2
Data Bit 1
Data Bit 0
-I/O CH RDY
AEN
Address 19
Address 18
Address 17
Address 16
Address 15
Address 14
Address 13
Address 12
Address 11
Address 10
Address 9
Address 8
Address 7
Address 6
Address 5
Address 4
Address 3
Address 2
Address 1
Address 0
Lower Signal
-CMD
-START
EXRDY
-EX32
Ground
KEY
-EX16
-SLBURST
-MSBURST
W-R
Ground
Reserved
Reserved
Reserved
Ground
KEY
-BE 1
Latch Address 31
Ground
-Latch Address 30
-Latch Address 28
-Latch Address 27
-Latch Address 25
Ground
KEY
Latch Address 15
Latch Address 13
Latch Address 12
Latch Address 11
Ground
Latch Address 9
2
3
4
5
F
1
1
2
2
3
3
4
4
5
5
8
9
10
11
12
13
14
15
18
19
20
21
22
23
24
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15
15
17
17
27
28
29
30
2
Figure 4.40
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
D16
D17
D18
D19
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
Pinouts for the EISA bus.
-SBHE
Latch Address 23
Latch Address 22
Latch Address 21
Latch Address 20
Latch Address 19
Latch Address 18
Latch Address 17
-MEMR
-MEMW
Data Bit 8
Data Bit 9
Data Bit 10
Data Bit 11
Data Bit 12
Data Bit 13
Data Bit 14
Data Bit 15
Latch Address 7
Ground
Latch Address 4
Latch Address 3
Ground
KEY
Data Bit 17
Data Bit 19
Data Bit 20
Data Bit 22
Ground
Data Bit 25
Data Bit 26
Data Bit 28
KEY
Ground
Data Bit 30
Data Bit 31
-MREQx
3
4
5
18
18
19
19
20
20
21
21
22
22
23
23
24
24
26
26
8
9
10
11
12
13
14
27
27
28
28
29
29
30
30
31
31
17
18
19
H
5
8
9
10
11
12
13
14
15
17
18
19
20
21
22
23
24
26
27
28
29
30
31
1
1
2
3
4
2
3
4
5
6
7
8
9
10
11
12
13
15
16
17
18
D
1
2
3
4
5
7
8
9
10
11
12
13
14
14
16
4
25
5
7
3
16
25
26
2
7
7
16
17
A
1
6
7
1
-MEM CS16
-I/O CS16
IRQ 10
IRQ 11
IRQ 12
IRQ 15
IRQ 14
-DACK 0
DRQ 0
-DACK 5
DRQ5
-DACK 6
DRQ 6
-DACK 7
DRQ 7
+5 Vdc
-Master
Ground
E
6
31
Latch Address 8
Latch Address 6
Latch Address 5
+5 Vdc
Latch Address 4
KEY
Data Bit 16
Data Bit 18
Ground
Data Bit 21
Data Bit 23
Data Bit 24
Ground
Data Bit 27
KEY
Data Bit 29
+5 Vdc
+5 Vdc
-MAKx
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G
15
16
17
18
C
Figure 4.41 The card
connector for the EISA bus.
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Automated Setup
EISA systems also use an automated setup to deal with adapter-board interrupts and addressing
issues. These issues often cause problems when several different adapter boards are installed in an
ISA system. EISA setup software recognizes potential conflicts and automatically configures the
system to avoid them. EISA does, however, enable you to do your own troubleshooting, as well as
to configure the boards through jumpers and switches. This concept was not new to EISA; IBM’s
MCA bus also supported configuration via software. Another new feature of EISA systems is IRQ
sharing, meaning that multiple bus cards can share a single interrupt. This feature has also been
implemented in PCI bus cards.
Similar to the MCA bus and the Reference disk required there, systems with an EISA bus require
an EISA Configuration disk, along with options disks containing files specific to each EISA
adapter installed. You can get the EISA Configuration disk from the manufacturer of your system
or motherboard and the Options disks from the manufacturer of the specific boards you are
using. Just as with MCA based systems, without these disks and files, you cannot properly configure an EISA system.
Note
Although automated setup traditionally has not been available in ISA systems, it is now available with Plug-andPlay (PnP) systems and components. PnP systems are discussed toward the end of this chapter in the section titled
“Plug-and-Play Systems.”
Local Buses
The I/O buses discussed so far (ISA, MCA, and EISA) have one thing in common: relatively slow
speed. The three newer bus types that we will look at in the following few sections all use the
local bus concept explained in this section to address the speed issue. The three main local buses
found in PC systems are
■ VL-Bus (VESA Local Bus)
■ PCI (Peripheral Component Interconnect)
■ AGP (Accelerated Graphics Port)
The speed limitation of ISA, MCA, and EISA is a carryover from the days of the original PC, when
the I/O bus operated at the same speed as the processor bus. As the speed of the processor bus
increased, the I/O bus realized only nominal speed improvements, primarily from an increase in
the bandwidth of the bus. The I/O bus had to remain at a slower speed, because the huge
installed base of adapter cards could operate only at slower speeds.
Figure 4.42 shows a conceptual block diagram of the buses in a computer system.
The thought of a computer system running slower than it could is very bothersome to some
computer users. Even so, the slow speed of the I/O bus is nothing more than a nuisance in most
cases. You don’t need blazing speed to communicate with a keyboard or mouse—you gain nothing in performance. The real problem occurs in subsystems in which you need the speed, such as
video and disk controllers.
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CPU
External
Cache
Processor
Bus
(High Speed)
Built-In
I/O
I/O Bus
(Slow Speed)
Bus
Controller
Chips
I/O Bus
Slotted
I/O
(Slow Speed)
Memory
Bus
(High Speed)
RAM
Figure 4.42
Bus layout in a traditional PC.
The speed problem became acute when graphical user interfaces (such as Windows) became
prevalent. These systems required the processing of so much video data that the I/O bus became
a literal bottleneck for the entire computer system. In other words, it did little good to have a
processor that was capable of 66MHz to 450MHz or faster if you could put data through the I/O
bus at a rate of only 8MHz.
An obvious solution to this problem is to move some of the slotted I/O to an area where it could
access the faster speeds of the processor bus—much the same way as the external cache. Figure
4.43 shows this arrangement.
This arrangement became known as local bus, because external devices (adapter cards) now could
access the part of the bus that was local to the CPU—the processor bus. Physically, the slots provided to tap this new configuration would need to be different from existing bus slots to prevent
adapter cards designed for slower buses from being plugged into the higher bus speeds, which
this design made accessible.
It is interesting to note that the very first 8-bit and 16-bit ISA buses were a form of local bus
architecture. These systems had the processor bus as the main bus, and everything ran at full
processor speeds. When ISA systems ran faster than 8MHz, the main ISA bus had to be decoupled
from the processor bus because expansion cards, memory, and so on could not keep up. In 1992,
an extension to the ISA bus called the VESA local bus (VL-Bus) started showing up on PC systems,
indicating a return to local bus architecture. Since then, the Peripheral Component Interconnect
(PCI) local bus has supplanted VL-Bus and the Accelerated Graphics Port (AGP) bus has been
introduced to complement PCI.
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CPU
External
Cache
Processor
Bus
(High Speed)
Slotted
I/O
Built-In
I/O
I/O Bus
(Slow Speed)
Bus
Controller
Chips
I/O Bus
Slotted
I/O
(Slow Speed)
Memory
Bus
(High Speed)
RAM
Figure 4.43
How a local bus works.
Note
A system does not have to have a local bus expansion slot to incorporate local bus technology; instead, the local
bus device can be built directly into the motherboard. (In such a case, the local bus-slotted I/O shown in Figure
4.41 would in fact be built-in I/O.) This built-in approach to local bus is the way the first local bus systems were
designed.
Local bus solutions do not replace earlier standards, such as ISA; they are designed into the system as a bus that is closer to the processor in the system architecture. Older buses such as ISA
have been kept around for backward compatibility with slower types of adapters that don’t need
any faster connection to the system (such as modems). Therefore, a typical system will have AGP,
PCI and ISA slots. Older cards still are compatible with the system, but high-speed adapter cards
can take advantage of the AGP and PCI local bus slots as well.
The performance of graphical user interfaces such as Windows and OS/2 have been tremendously
improved by moving the video cards off of the slow ISA bus and onto faster PCI and now AGP
local buses.
VESA Local Bus
The VESA local bus was the most popular local bus design from its debut in August 1992 through
1994. It was created by the VESA committee, a non-profit organization founded by NEC to further develop video display and bus standards. In a similar fashion to how EISA evolved, NEC had
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done most of the work on the VL-Bus (as it would be called), and after founding the non-profit
VESA committee, they turned over future development to VESA. At first, the local bus slot
seemed primarily designed to be used for video cards. Improving video performance was a top
priority at NEC to help sell their high-end displays as well as their own PC systems. By 1991,
video performance had become a real bottleneck in most PC systems.
The Video Electronics Standards Association (VESA) developed a standardized local bus specification known as VESA local bus (VL-Bus). As in earlier local bus implementations, the VL-Bus slot
offers direct access to system memory at the speed of the processor itself. The VL-Bus can move
data 32 bits at a time, enabling data to flow between the CPU and a compatible video subsystem
or hard drive at the full 32-bit data width of the 486 chip. The maximum rated throughput of the
VL-Bus is 128MB to 132MB/sec. In other words, local bus went a long way toward removing the
major bottlenecks that existed in earlier bus configurations.
Additionally, VL-Bus offers manufacturers of hard-drive interface cards an opportunity to overcome another traditional bottleneck: the rate at which data can flow between the hard drive and
the CPU. The average 16-bit IDE drive and interface can achieve throughput of up to 5MB/sec,
whereas VL-Bus hard drive adapters for IDE drives are touted as providing throughput of as much
as 8MB/sec. In real-world situations, the true throughput of VL-Bus hard drive adapters is somewhat less than 8MB/sec, but VL-Bus still provides a substantial boost in hard-drive performance.
Despite all the benefits of the VL-Bus (and, by extension, of all local buses), this technology has a
few drawbacks, which are described in the following list:
■ Dependence on a 486 CPU. The VL-Bus inherently is tied to the 486 processor bus. This bus
is quite different from that used by Pentium and later processors. A VL-Bus that operates at
the full rated speed of a Pentium has not been developed, although stopgap measures (such
as stepping down speed or developing bus bridges) are available. Unfortunately, these result
in poor performance. Some systems have been developed with both VL-Bus and PCI slots,
but because of design compromises, performance often suffers.
■ Speed limitations. The VL-Bus specification provides for speeds of up to 66MHz on the bus,
but the electrical characteristics of the VL-Bus connector limit an adapter card to no more
than 40–50MHz. In practice, running the VL-Bus at speeds over 33MHz cause many problems, so 33MHz has become the acceptable speed limit. Systems that use faster processor
bus speeds must buffer and step down the clock on the VL-Bus or add wait states. Note that
if the main CPU uses a clock modifier (such as the kind that doubles clock speeds), the VLBus uses the unmodified CPU clock speed as its bus speed.
■ Electrical limitations. The processor bus has very tight timing rules that may vary from CPU
to CPU. These timing rules were designed for limited loading on the bus, meaning that the
only elements originally intended to be connected to the local bus are elements such as the
external cache and the bus controller chips. As you add more circuitry, you increase the
electrical load. If the local bus is not implemented correctly, the additional load can lead to
problems such as loss of data integrity and timing problems between the CPU and the VLBus cards.
■ Card limitations. Depending on the electrical loading of a system, the number of VL-Bus
cards is limited. Although the VL-Bus specification provides for as many as three cards, this
can be achieved only at clock rates of up to 40MHz with an otherwise low system-board
load. As the system-board load and clock rate increases, the number of cards supported
decreases. Only one VL-Bus card can be supported at 50MHz with a high system-board
load. In practice, these limits could not usually be reached without problems.
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The VL-Bus did not seem to be a well-engineered concept. The design was simple indeed—just
take the pins from the 486 processor and run them out to a card connector socket. In other
words, the VL-Bus is essentially the raw 486 processor bus. This allowed a very inexpensive
design, because no additional chipsets or interface chips were required. A motherboard designer
could add VL-Bus slots to their 486 motherboards very easily and at a very low cost. This is why
these slots appeared on virtually all 486 system designs overnight.
Unfortunately, the 486 processor bus was not designed to have multiple devices (called loads)
plugged into it at one time. Problems arose with timing glitches caused by the capacitance introduced into the circuit by different cards. Since the VL-Bus ran at the same speed as the processor
bus, different processor speeds meant different bus speeds and full compatibility was difficult to
achieve. Although the VL-Bus could be adapted to other processors, including the 386 or even
the Pentium, it was designed for the 486, and worked best as a 486 solution only. Despite the low
cost, after a new bus called PCI (Peripheral Component Interconnect) appeared, VL-Bus fell into disfavor very quickly. It never did catch on with Pentium systems, and there is little or no further
development of the VL-Bus in the PC industry. I would not recommend purchasing VL-Bus cards
or systems today.
For a used system, or as an inexpensive upgrade for an older system, VL-Bus might be appropriate
and can provide an acceptable solution for high-speed computing.
Physically, the VL-Bus slot is an extension of the slots used for whatever type of base system you
have. If you have an ISA system, the VL-Bus is positioned as an extension of your existing 16-bit
ISA slots. Likewise, if you have an EISA system or MCA system, the VL-Bus slots are extensions of
those existing slots. Figure 4.44 shows how the VL-Bus slots could be situated in an ISA system.
The VESA extension has 112 contacts and uses the same physical connector as the MCA bus.
The VL-Bus adds a total 116 pin locations to the bus connectors that your system already has.
Table 4.25 lists the pinouts for only the VL-Bus connector portion of the total connector. (For
pins for which two purposes are listed, the second purpose applies when the card is in 64-bit
transfer mode.)
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Regular
Slots
CPU
VL-Bus
Slots
Figure 4.44
An example of VL-Bus slots in an ISA system.
297
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Table 4.25
Pinouts for the VL-Bus
Pin
Signal
Pin
Signal
B1
Data 0
A1
Data 1
B2
Data 2
A2
Data 3
B3
Data 4
A3
Ground
B4
Data 6
A4
Data 5
B5
Data 8
A5
Data 7
B6
Ground
A6
Data 9
B7
Data 10
A7
Data 11
B8
Data 12
A8
Data 13
B9
VCC
A9
Data 15
B10
Data 14
A10
Ground
B11
Data 16
A11
Data 17
B12
Data 18
A12
VCC
B13
Data 20
A13
Data 19
B14
Ground
A14
Data 21
B15
Data 22
A15
Data 23
B16
Data 24
A16
Data 25
B17
Data 26
A17
Ground
B18
Data 28
A18
Data 27
B19
Data 30
A19
Data 29
B20
VCC
A20
Data 31
B21
Address 31 or Data 63
A21
Address 30 or Data 62
B22
Ground
A22
Address 28 or Data 60
B23
Address 29 or Data 61
A23
Address 26 or Data 58
B24
Address 27 or Data 59
A24
Ground
B25
Address 25 or Data 57
A25
Address 24 or Data 56
B26
Address 23 or Data 55
A26
Address 22 or Data 54
B27
Address 21 or Data 53
A27
VCC
B28
Address 19 or Data 51
A28
Address 20 or Data 52
B29
Ground
A29
Address 18 or Data 50
B30
Address 17 or Data 49
A30
Address 16 or Data 48
B31
Address 15 or Data 47
A31
Address 14 or Data 46
B32
VCC
A32
Address 12 or Data 44
B33
Address 13 or Data 45
A33
Address 10 or Data 42
B34
Address 11 or Data 43
A34
Address 8 or Data 40
B35
Address 9 or Data 41
A35
Ground
B36
Address 7 or Data 39
A36
Address 6 or Data 38
B37
Address 5 or Data 37
A37
Address 4 or Data 36
B38
Ground
A38
Write Back
B39
Address 3 or Data 35
A39
Byte Enable 0 or 4
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Pin
Chapter 4
Pin
Signal
B40
Address 2 or Data 34
A40
VCC
B41
Unused or LBS64#
A41
Byte Enable 1 or 5
B42
Reset
A42
Byte Enable 2 or 6
B43
Data/Code Status
A43
Ground
B44
Memory-I/O Status or Data 33
A44
Byte Enable 3 or 7
B45
Write/Read Status or Data 32
A45
Address Data Strobe
B46
Access key
A46
Access key
B47
Access key
A47
Access key
B48
Ready Return
A48
Local Ready
B49
Ground
A49
Local Device
B50
IRQ 9
A50
Local Request
B51
Burst Ready
A51
Ground
299
Signal
B52
Burst Last
A52
Local Bus Grant
B53
ID0
A53
VCC
B54
ID1
A54
ID2
B55
Ground
A55
ID3
B56
Local Clock
A56
ID4 or ACK64#
B57
VCC
A57
Unused
B58
Local Bus Size 16
A58
Loc/Ext Address Data Strobe
Figure 4.45 shows the locations of the pins.
B58
B48
B45
B1
A58
A48
A45
A1
Figure 4.45
Toward Main
I/O Bus
Connector
The card connector for the VL-Bus.
The PCI Bus
In early 1992, Intel spearheaded the creation of another industry group. It was formed with the
same goals as the VESA group in relation to the PC bus. Recognizing the need to overcome weaknesses in the ISA and EISA buses, the PCI Special Interest Group was formed.
The Peripheral Component Interconnect (PCI) bus specification was released in June 1992 as version 1.0; it was later updated in April 1993 as version 2.0, and in early 1995 the latest revision 2.1
appeared. PCI redesigned the traditional PC bus by inserting another bus between the CPU and
the native I/O bus by means of bridges. Rather than tap directly into the processor bus, with its
delicate electrical timing (as was done in the VL-Bus), a new set of controller chips was developed
to extend the bus, as shown in Figure 4.46.
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Processor
Cache
Bridge/
Memory
Controller
DRAM
Audio
Motion
Video
PCI LOCAL BUS
LAN
SCSI
EXP Bus
XFACE
Graphics
Base I/O
Functions
ISA/EISA - Microchannel
Figure 4.46
Conceptual diagram of the PCI bus.
The PCI bus often is called a mezzanine bus because it adds another layer to the traditional bus
configuration. PCI bypasses the standard I/O bus; it uses the system bus to increase the bus clock
speed and take full advantage of the CPU’s data path. Systems that integrate the PCI bus became
available in mid 1993 and have since become the mainstay high-end systems.
Information is transferred across the PCI bus at 33MHz, at the full data width of the CPU. When
the bus is used in conjunction with a 32-bit CPU, the bandwidth is 132MB per second, as the following formula shows:
33MHz×32 bits = 1,056Mbit/sec
1,056Mbit/sec÷8 = 132MB/sec
When the bus is used in future 64-bit implementations, the bandwidth doubles, meaning that
you can transfer data at speeds up to 264MB/sec. Real-life data transfer speeds necessarily will be
lower, but still much faster than anything else that is currently available. Part of the reason for
this faster real-life throughput is the fact that the PCI bus can operate concurrently with the
processor bus; it does not supplant it. The CPU can be processing data in an external cache while
the PCI bus is busy transferring information between other parts of the system—a major design
benefit of the PCI bus.
A PCI adapter card uses its own unique connector. This connector can be identified within a
computer system because it typically is offset from the normal ISA, MCA, or EISA connectors. See
Figure 4.47 for an example. The size of a PCI card can be the same as that of the cards used in the
system’s normal I/O bus.
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PCI Slots
ISA or
EISA Slots
Figure 4.47
Possible configuration of PCI slots in relation to ISA or EISA slots.
The PCI specification identifies three board configurations, each designed for a specific type of
system with specific power requirements. The 5v specification is for stationary computer systems,
the 3.3v specification is for portable machines, and the universal specification is for motherboards and cards that work in either type of system.
Table 4.26 shows the 5v PCI pinouts, and Figure 4.48 shows the pin locations. Table 4.27 shows
the 3.3v PCI pinouts; the pin locations are indicated in Figure 4.49. Finally, Table 4.28 shows the
pinouts, and Figure 4.50 shows the pin locations for a universal PCI slot and card. Notice that
each figure shows both the 32-bit and 64-bit variations on the respective specifications.
Note
If the PCI card supports only 32 data bits, it needs only pins B1/A1 through B62/A62. Pins B63/A63 through
B94/A94 are used only if the card supports 64 data bits.
Table 4.26
Pin
Pinouts for a 5v PCI Bus
Signal Name
Pin
Signal Name
B1
–12v
A1
Test Reset
B2
Test Clock
A2
+12v
B3
Ground
A3
Test Mode Select
(continues)
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Motherboards and Buses
Continued
Pin
Signal Name
Pin
Signal Name
B4
Test Data Output
A4
Test Data Input
B5
+5v
A5
+5v
B6
+5v
A6
Interrupt A
B7
Interrupt B
A7
Interrupt C
B8
Interrupt D
A8
+5v
B9
PRSNT1#
A9
Reserved
B10
Reserved
A10
+5v I/O
B11
PRSNT2#
A11
Reserved
B12
Ground
A12
Ground
B13
Ground
A13
Ground
B14
Reserved
A14
Reserved
B15
Ground
A15
Reset
B16
Clock
A16
+5v I/O
B17
Ground
A17
Grant
B18
Request
A18
Ground
B19
+5v I/O
A19
Reserved
B20
Address 31
A20
Address 30
B21
Address 29
A21
+3.3v
B22
Ground
A22
Address 28
B23
Address 27
A23
Address 26
B24
Address 25
A24
Ground
B25
+3.3v
A25
Address 24
B26
C/BE 3
A26
Init Device Select
B27
Address 23
A27
+3.3v
B28
Ground
A28
Address 22
B29
Address 21
A29
Address 20
B30
Address 19
A30
Ground
B31
+3.3v
A31
Address 18
B32
Address 17
A32
Address 16
B33
C/BE 2
A33
+3.3v
B34
Ground
A34
Cycle Frame
B35
Initiator Ready
A35
Ground
B36
+3.3v
A36
Target Ready
B37
Device Select
A37
Ground
B38
Ground
A38
Stop
B39
Lock
A39
+3.3v
B40
Parity Error
A40
Snoop Done
B41
+3.3v
A41
Snoop Backoff
B42
System Error
A42
Ground
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Pin
Signal Name
Pin
Signal Name
B43
+3.3v
A43
PAR
B44
C/BE 1
A44
Address 15
B45
Address 14
A45
+3.3v
B46
Ground
A46
Address 13
B47
Address 12
A47
Address 11
B48
Address 10
A48
Ground
B49
Ground
A49
Address 9
B50
Access key
A50
Access key
B51
Access key
A51
Access key
B52
Address 8
A52
C/BE 0
B53
Address 7
A53
+3.3v
B54
+3.3v
A54
Address 6
B55
Address 5
A55
Address 4
B56
Address 3
A56
Ground
B57
Ground
A57
Address 2
B58
Address 1
A58
Address 0
B59
+5v I/O
A59
+5v I/O
B60
Acknowledge 64-bit
A60
Request 64-bit
B61
+5v
A61
+5v
B62
+5v Access key
A62
+5v Access key
B63
Reserved
A63
Ground
B64
Ground
A64
C/BE 7
B65
C/BE 6
A65
C/BE 5
B66
C/BE 4
A66
+5v I/O
B67
Ground
A67
Parity 64-bit
B68
Address 63
A68
Address 62
B69
Address 61
A69
Ground
B70
+5v I/O
A70
Address 60
B71
Address 59
A71
Address 58
B72
Address 57
A72
Ground
B73
Ground
A73
Address 56
B74
Address 55
A74
Address 54
B75
Address 53
A75
+5v I/O
B76
Ground
A76
Address 52
B77
Address 51
A77
Address 50
B78
Address 49
A78
Ground
B79
+5v I/O
A79
Address 48
B80
Address 47
A80
Address 46
B81
Address 45
A81
Ground
Chapter 4
303
(continues)
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Continued
Pin
Signal Name
Pin
Signal Name
B82
Ground
A82
Address 44
B83
Address 43
A83
Address 42
B84
Address 41
A84
+5v I/O
B85
Ground
A85
Address 40
B86
Address 39
A86
Address 38
B87
Address 37
A87
Ground
B88
+5v I/O
A88
Address 36
B89
Address 35
A89
Address 34
B90
Address 33
A90
Ground
B91
Ground
A91
Address 32
B92
Reserved
A92
Reserved
B93
Reserved
A93
Ground
B94
Ground
A94
Reserved
B1
A1
A52
A49
B52
A62
B49
B62
Rear
of the
Computer
32-bit Connector
A52
A1
B52
A62
B1
B62
A63
A49
B63
A94
B49
B94
64-bit Connector
Figure 4.48
Table 4.27
Pin
The 5v PCI slot and card configuration.
Pinouts for a 3.3v PCI Bus
Signal Name
Pin
Signal Name
B1
–12v
A1
Test Reset
B2
Test Clock
A2
+12v
B3
Ground
A3
Test Mode Select
B4
Test Data Output
A4
Test Data Input
B5
+5v
A5
+5v
B6
+5v
A6
Interrupt A
B7
Interrupt B
A7
Interrupt C
B8
Interrupt D
A8
+5v
Rear
of the
Computer
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Pin
Signal Name
Pin
Signal Name
B9
PRSNT1#
A9
Reserved
B10
Reserved
A10
+3.3v
B11
PRSNT2#
A11
Reserved
B12
Access key
A12
Access key
B13
Access key
A13
Access key
B14
Reserved
A14
Reserved
B15
Ground
A15
Reset
B16
Clock
A16
+3.3v
B17
Ground
A17
Grant
B18
Request
A18
Ground
B19
+3.3v
A19
Reserved
B20
Address 31
A20
Address 30
B21
Address 29
A21
+3.3v
B22
Ground
A22
Address 28
B23
Address 27
A23
Address 26
B24
Address 25
A24
Ground
B25
+3.3v
A25
Address 24
B26
C/BE 3
A26
Init Device Select
B27
Address 23
A27
+3.3v
B28
Ground
A28
Address 22
B29
Address 21
A29
Address 20
B30
Address 19
A30
Ground
B31
+3.3v
A31
Address 18
B32
Address 17
A32
Address 16
B33
C/BE 2
A33
+3.3v
B34
Ground
A34
Cycle Frame
B35
Initiator Ready
A35
Ground
B36
+3.3v
A36
Target Ready
B37
Device Select
A37
Ground
B38
Ground
A38
Stop
B39
Lock
A39
+3.3v
B40
Parity Error
A40
Snoop Done
B41
+3.3v
A41
Snoop Backoff
B42
System Error
A42
Ground
B43
+3.3v
A43
PAR
B44
C/BE 1
A44
Address 15
B45
Address 14
A45
+3.3v
B46
Ground
A46
Address 13
B47
Address 12
A47
Address 11
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(continues)
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Continued
Pin
Signal Name
Pin
Signal Name
B48
Address 10
A48
Ground
B49
Ground
A49
Address 9
B50
Ground
A50
Ground
B51
Ground
A51
Ground
B52
Address 8
A52
C/BE 0
B53
Address 7
A53
+3.3v
B54
+3.3v
A54
Address 6
B55
Address 5
A55
Address 4
B56
Address 3
A56
Ground
B57
Ground
A57
Address 2
B58
Address 1
A58
Address 0
B59
+3.3v
A59
+3.3v
B60
Acknowledge 64-bit
A60
Request 64-bit
B61
+5v
A61
+5v
B62
+5v Access key
A62
+5v Access key
B63
Reserved
A63
Ground
B64
Ground
A64
C/BE 7
B65
C/BE 6
A65
C/BE 5
B66
C/BE 4
A66
+3.3v
B67
Ground
A67
Parity 64-bit
B68
Address 63
A68
Address 62
B69
Address 61
A69
Ground
B70
+3.3v
A70
Address 60
B71
Address 59
A71
Address 58
B72
Address 57
A72
Ground
B73
Ground
A73
Address 56
B74
Address 55
A74
Address 54
B75
Address 53
A75
+3.3v
B76
Ground
A76
Address 52
B77
Address 51
A77
Address 50
B78
Address 49
A78
Ground
B79
+3.3v
A79
Address 48
B80
Address 47
A80
Address 46
B81
Address 45
A81
Ground
B82
Ground
A82
Address 44
B83
Address 43
A83
Address 42
B84
Address 41
A84
+3.3v
B85
Ground
A85
Address 40
B86
Address 39
A86
Address 38
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Pin
Signal Name
Pin
Signal Name
B87
Address 37
A87
Ground
B88
+3.3v
A88
Address 36
B89
Address 35
A89
Address 34
B90
Address 33
A90
Ground
B91
Ground
A91
Address 32
B92
Reserved
A92
Reserved
B93
Reserved
A93
Ground
B94
Ground
A94
Reserved
307
B1
A11
A1
B11
B1
A11
A1
A49
B11
B49
A52
A14
B52
A62
B14
B62
Rear
of the
Computer
32-bit Connector
B62
B52
B49
A63
A62
A52
A49
A14
B63
A94
B14
B94
Rear
of the
Computer
64-bit Connector
Figure 4.49
The 3.3v PCI slot and card configuration.
Table 4.28
Pinouts for a Universal PCI Bus
Pin
Signal Name
Pin
Signal Name
B1
–12v
A1
Test Reset
B2
Test Clock
A2
+12v
B3
Ground
A3
Test Mode Select
B4
Test Data Output
A4
Test Data Input
B5
+5v
A5
+5v
B6
+5v
A6
Interrupt A
B7
Interrupt B
A7
Interrupt C
B8
Interrupt D
A8
+5v
B9
PRSNT1#
A9
Reserved
B10
Reserved
A10
+v I/O
B11
PRSNT2#
A11
Reserved
B12
Access key
A12
Access key
B13
Access key
A13
Access key
(continues)
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Continued
Pin
Signal Name
Pin
Signal Name
B14
Reserved
A14
Reserved
B15
Ground
A15
Reset
B16
Clock
A16
+v I/O
B17
Ground
A17
Grant
B18
Request
A18
Ground
B19
+v I/O
A19
Reserved
B20
Address 31
A20
Address 30
B21
Address 29
A21
+3.3v
B22
Ground
A22
Address 28
B23
Address 27
A23
Address 26
B24
Address 25
A24
Ground
B25
+3.3v
A25
Address 24
B26
C/BE 3
A26
Init Device Select
B27
Address 23
A27
+3.3v
B28
Ground
A28
Address 22
B29
Address 21
A29
Address 20
B30
Address 19
A30
Ground
B31
+3.3v
A31
Address 18
B32
Address 17
A32
Address 16
B33
C/BE 2
A33
+3.3v
B34
Ground
A34
Cycle Frame
B35
Initiator Ready
A35
Ground
B36
+3.3v
A36
Target Ready
B37
Device Select
A37
Ground
B38
Ground
A38
Stop
B39
Lock
A39
+3.3v
B40
Parity Error
A40
Snoop Done
B41
+3.3v
A41
Snoop Backoff
B42
System Error
A42
Ground
B43
+3.3v
A43
PAR
B44
C/BE 1
A44
Address 15
B45
Address 14
A45
+3.3v
B46
Ground
A46
Address 13
B47
Address 12
A47
Address 11
B48
Address 10
A48
Ground
B49
Ground
A49
Address 9
B50
Access key
A50
Access key
B51
Access key
A51
Access key
B52
Address 8
A52
C/BE 0
B53
Address 7
A53
+3.3v
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Pin
Signal Name
Pin
Signal Name
B54
+3.3v
A54
Address 6
B55
Address 5
A55
Address 4
B56
Address 3
A56
Ground
B57
Ground
A57
Address 2
B58
Address 1
A58
Address 0
B59
+5 I/O
A59
+v I/O
B60
Acknowledge 64-bit
A60
Request 64-bit
B61
+5v
A61
+5v
B62
+5v Access key
A62
+5v Access key
B63
Reserved
A63
Ground
B64
Ground
A64
C/BE 7
B65
C/BE 6
A65
C/BE 5
B66
C/BE 4
A66
+v I/O
B67
Ground
A67
Parity 64-bit
B68
Address 63
A68
Address 62
B69
Address 61
A69
Ground
B70
+v I/O
A70
Address 60
B71
Address 59
A71
Address 58
B72
Address 57
A72
Ground
B73
Ground
A73
Address 56
B74
Address 55
A74
Address 54
B75
Address 53
A75
+v I/O
B76
Ground
A76
Address 52
B77
Address 51
A77
Address 50
B78
Address 49
A78
Ground
B79
+v I/O
A79
Address 48
B80
Address 47
A80
Address 46
B81
Address 45
A81
Ground
B82
Ground
A82
Address 44
B83
Address 43
A83
Address 42
B84
Address 41
A84
+v I/O
B85
Ground
A85
Address 40
B86
Address 39
A86
Address 38
B87
Address 37
A87
Ground
B88
+v I/O
A88
Address 36
B89
Address 35
A89
Address 34
B90
Address 33
A90
Ground
B91
Ground
A91
Address 32
B92
Reserved
A92
Reserved
B93
Reserved
A93
Ground
B94
Ground
A94
Reserved
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A1
B11
B1
A11
A1
B1
A11
B11
A14
A49
B14
B49
A52
A14
B52
A62
B14
B62
Rear
of the
Computer
32-bit Connector
B94
B63
B62
B52
B49
A94
A63
A62
A52
A49
Rear
of the
Computer
64-bit Connector
Figure 4.50
The universal PCI slot and card configuration.
Notice that the universal PCI board specifications effectively combine the 5v and 3.3v specifications. For pins for which the voltage is different, the universal specification labels the pin simply
V I/O. This type of pin represents a special power pin for defining and driving the PCI signaling
rail.
Another important feature of PCI is the fact that it was the model for the Intel PnP specification.
This means that PCI cards do not have jumpers and switches, and are instead configured through
software. True PnP systems are capable of automatically configuring the adapters, while non-PnP
systems with ISA slots have to configure the adapters through a program that is usually a part of
the system CMOS configuration. Starting in late 1995, most PC-compatible systems have
included a PnP BIOS that allows the automatic PnP configuration.
Accelerated Graphics Port (AGP)
The Accelerated Graphics Port (AGP) was created by Intel as a new bus specifically designed for
high performance graphics and video support. AGP is based on PCI, but contains a number of
additions and enhancements, and is physically, electrically, and logically independent of PCI. For
example the AGP connector is similar to PCI, although it has additional signals and is positioned
differently in the system. Unlike PCI, which is a true bus with multiple connectors (slots), AGP is
more of a point-to-point high performance connection designed specifically for a video card in a
system, as only one AGP slot is allowed for a single video card.
The AGP specification 1.0 was originally released by Intel in July of 1996, and defined a 66MHz
clock rate with 1x or 2x signaling using 3.3 volts. AGP version 2.0 was released in May 1998, and
added 4x signaling as well as a lower 1.5v operating capability. There is also a new AGP Pro specification that defines a slightly longer slot with additional power pins at each end to drive bigger
and faster AGP cards which consume more than 25 watts of power, up to a maximum of 110
watts. AGP Pro cards would likely be used for high-end graphics workstations. AGP Pro slots are
backward compatible, meaning standard AGP card will plug in.
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AGP is a high-speed connection, and runs at a base frequency of 66MHz (actually 66.66MHz),
which is double that of standard PCI. In the basic AGP mode called 1x, a single transfer is done
every cycle. Since the AGP bus is 32 bits (4 bytes) wide, at 66 million times per second it would
be capable of transferring data at a rate of about 266MB/sec (million bytes per second)! The original AGP specification also defines a 2x mode, where two transfers are done every cycle, resulting
in 533 MB/sec. Using an analogy where every cycle is equivalent to the back and forth swing of a
pendulum, the 1x mode is thought of as transferring information at the start of each swing. In 2x
mode, an additional transfer would occur every time the pendulum completed half a swing,
thereby doubling performance while technically maintaining the same clock rate, or in this case,
the same number of swings per second. Most modern AGP cards work in the 2x mode.
The newer AGP 2.0 specification adds the capability for 4x transfers, which transfers data four
times per cycle and equals a data transfer rate of 1,066 MB/sec. The Table 4.29 shows the differences in clock rates and data transfer speeds for the various AGP modes.
Table 4.29
Clock Rates Versus Data Transfer Speeds
AGP Mode
Base Clock
Rate
Effective
Clock Rate
Data Transfer
Rate
1x
66MHz
66MHz
266MB/sec
2x
66MHz
133MHz
533MB/sec
4x
66MHz
266MHz
1,066MB/sec
Because AGP is independent of PCI, using an AGP video card will free up the PCI bus for more
traditional input and output, such as for IDE/ATA or SCSI controllers, USB controllers, sound
cards, etc.
Besides faster video performance, one of the main reasons Intel designed AGP was to allow the
video card to have a high-speed connection directly to the system RAM. This will allow an AGP
video card to have direct access to the system RAM, reducing the need for more and more video
memory. This is especially important because memory hungry 3D video becomes more and more
prevalent on PCs.
AGP will allow the speed of the video card to pace the requirements for high-speed 3D graphics
rendering as well as full motion video on the PC in the future.
System Resources
System resources are the communications channels, addresses, and other signals used by hardware devices to communicate on the bus. At their lowest level, these resources typically include
the following:
■ Memory addresses
■ IRQ (interrupt request) channels
■ DMA (direct memory access) channels
■ I/O port addresses
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I have listed these roughly in the order you would experience problems with them. Memory conflicts are perhaps the most troublesome of these, certainly the most difficult to fully explain and
overcome. These are discussed in Chapter 6, “Memory,” which focuses on the others listed here
in the order you will likely have problems with them.
IRQs cause more problems than DMA because they are in much higher demand; therefore, virtually all cards will use IRQ channels. There are fewer problems with DMA channels because few
cards use them, and there are usually more than enough channels to go around. I/O ports are
used by all hardware devices on the bus, but there are technically 64KB of them, which means
plenty to go around. With all these resources, you have to make sure that a unique card or hardware function uses each resource; in most cases they cannot or should not be shared.
These resources are required and used by many different components of your system. Adapter
cards need these resources to communicate with your system and accomplish their purposes. Not
all adapter cards have the same resource requirements. A serial communications port, for example, needs an IRQ channel and I/O port address, whereas a soundboard needs these resources and
normally at least one DMA channel as well. Most network cards use a 16KB block of memory
addresses, an IRQ channel, and an I/O port address.
As your system increases in complexity, the chance for resource conflicts increases dramatically.
Modern systems with sound cards and network cards can really push the envelope and become a
configuration nightmare for the uninitiated. So that you can resolve conflicts, most adapter cards
allow you to modify resource assignments by using the Plug-and-Play software that comes with
the card or the device manager in Windows 95 and later. Even if the automatic configuration gets
confused (which happens more often than it should), fortunately, in almost all cases there is a
logical way to configure the system—once you know the rules.
Interrupts (IRQs)
Interrupt request channels (IRQs), or hardware interrupts, are used by various hardware devices to
signal the motherboard that a request must be fulfilled. This procedure is the same as a student
raising his hand to indicate that he needs attention.
These interrupt channels are represented by wires on the motherboard and in the slot connectors. When a particular interrupt is invoked, a special routine takes over the system, which first
saves all the CPU register contents in a stack, and then directs the system to the interrupt vector
table. This vector table contains a list of memory addresses that correspond to the interrupt channels. Depending on which interrupt was invoked, the program corresponding to that channel is
run.
The pointers in the vector table point to the address of whatever software driver is used to service the card that generated the interrupt. For a network card, for example, the vector may
point to the address of the network drivers that have been loaded to operate the card; for a hard
disk controller, the vector may point to the BIOS code that operates the controller.
After the particular software routine finishes performing whatever function the card needed, the
interrupt-control software returns the stack contents to the CPU registers, and the system then
resumes whatever it was doing before the interrupt occurred.
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Through the use of interrupts, your system can respond to external events in a timely fashion.
Each time a serial port presents a byte to your system, an interrupt is generated to ensure that the
system reads that byte before another comes in. Keep in mind that in some cases a port device—
in particular, a modem with a 16550 or higher UART chip—may incorporate a byte buffer that
allows multiple characters to be stored before an interrupt is generated.
Hardware interrupts are generally prioritized by their numbers; with some exceptions, the highest-priority interrupts have the lowest numbers. Higher-priority interrupts take precedence over
lower-priority interrupts by interrupting them. As a result, several interrupts can occur in your
system concurrently, each interrupt nesting within another.
If you overload the system—in this case, by running out of stack resources (too many interrupts
were generated too quickly)—an internal stack overflow error occurs and your system halts. The
message usually appears as Internal stack overflow - system halted at a DOS prompt. If you
experience this type of system error and run DOS, you can compensate for it by using the STACKS
parameter in your CONFIG.SYS file to increase the available stack resources. Most people will not
see this error in Windows 95 or Windows NT.
The ISA bus uses edge-triggered interrupt sensing, in which an interrupt is sensed by a signal sent
on a particular wire located in the slot connector. A different wire corresponds to each possible
hardware interrupt. Because the motherboard cannot recognize which slot contains the card that
used an interrupt line and therefore generated the interrupt, confusion would result if more than
one card were set to use a particular interrupt. Each interrupt, therefore, usually is designated for
a single hardware device. Most of the time, interrupts cannot be shared.
A device can be designed to share interrupts, and a few devices allow this; but, most cannot
because of the way interrupts are signaled in the ISA bus. The PCI bus allows interrupt sharing, in
fact, virtually all PCI cards are set to PCI interrupt A, and share that interrupt on the PCI bus. The
real problem is that there are technically two sets of hardware interrupts in the system, PCI interrupts and ISA interrupts. For PCI cards to work in a PC, the PCI interrupts must be mapped to ISA
interrupts, which are normally non-shareable. This means in many cases you would have to
assign a non-conflicting interrupt for each card.
The solution to the interrupt sharing problem for PCI cards is something called PCI IRQ Steering,
which is supported in newer operating systems and BIOS. PCI IRQ Steering allows a plug-andplay operating system such as Windows to dynamically map or steer PCI cards (which all use PCI
INTA#) to ISA interrupts, and allows several PCI cards to be mapped to the same ISA interrupt.
More information on PCI IRQ Steering is found in the section on PCI interrupts later in this
chapter.
Hardware interrupts are sometimes referred to as maskable interrupts, which means that the interrupts can be masked or turned off for a short time while the CPU is used for other critical operations. It is up to the system BIOS and programs to manage interrupts properly and efficiently for
the best system performance.
Because interrupts usually cannot be shared in an ISA bus system, you often run into conflicts
and can even run out of interrupts when you are adding boards to a system. If two boards use the
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same IRQ to signal the system, the resulting conflict prevents either board from operating properly. The following sections discuss the IRQs that any standard devices use, as well as what may
be free in your system.
8-Bit ISA Bus Interrupts
The PC and XT (the systems based on the 8-bit 8086 CPU) provide for eight different external
hardware interrupts. Table 4.30 shows the typical uses for these interrupts, which are numbered
0–7.
Table 4.30
8-Bit ISA Bus Default Interrupt Assignments
IRQ
Function
Bus Slot
0
System Timer
No
1
Keyboard Controller
No
2
Available
Yes (8-bit)
3
Serial Port 2 (COM2:)
Yes (8-bit)
4
Serial Port 1 (COM1:)
Yes (8-bit)
5
Hard Disk Controller
Yes (8-bit)
6
Floppy Disk Controller
Yes (8-bit)
7
Parallel Port 1 (LPT1:)
Yes (8-bit)
If you have a system that has one of the original 8-bit ISA buses, you will find that the IRQ
resources provided by the system present a severe limitation. Installing several devices that need
the services of system IRQs in a PC/XT-type system can be a study in frustration, because the only
way to resolve the interrupt-shortage problem is to remove the adapter board that you need the
least.
16-Bit ISA, EISA, and MCA Bus Interrupts
The introduction of the AT, based on the 286 processor, was accompanied by an increase in the
number of external hardware interrupts that the bus would support. The number of interrupts
was doubled to 16 by using two Intel 8259 interrupt controllers, piping the interrupts generated
by the second one through the unused IRQ 2 in the first controller. This arrangement effectively
means that only 15 IRQ assignments are available, and IRQ 2 effectively became inaccessible.
By routing all the interrupts from the second IRQ controller through IRQ 2 on the first, all these
new interrupts are assigned a nested priority level between IRQ 1 and IRQ 3. Thus, IRQ 15 ends
up having a higher priority than IRQ 3. Figure 4.51 shows how the two 8259 chips were wired to
create the cascade through IRQ 2 on the first chip.
To prevent problems with boards set to use IRQ 2, the AT system designers routed one of the new
interrupts (IRQ 9) to fill the slot position left open after removing IRQ 2. This means that any
card you install in a modern system that claims to use IRQ 2 is really using IRQ 9 instead. Some
cards now label this selection as IRQ 2/9, while others may only call it IRQ 2 or IRQ 9. No matter
what the labeling says, you must never set two cards to use that interrupt!
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INT
To CPU
315
From Timer Circuits
From Keyboard Controller
From FPU
From RTC/CMOS
8259 PIC (#1)
0
1
2
3
4
5
6
7
Chapter 4
IRQ 0
IRQ 1
8259 PIC (#2)
IRQ
IRQ
IRQ
IRQ
IRQ
3
4
5
6
7
INT
From 8-bit slots
0
1
2
3
4
5
6
7
IRQ
IRQ
IRQ
IRQ
IRQ
IRQ
IRQ
IRQ
8
9
10
11
12
13
14
15
From 16-bit slots
From 8-bit slots (former IRQ 2 pin position)
Figure 4.51
Interrupt controller cascade wiring.
Table 4.31 shows the typical uses for interrupts in the 16-bit ISA, EISA, and MCA buses, and lists
them in priority order from highest to lowest.
Table 4.31
16/32-Bit ISA/PCI Default Interrupt Assignments
IRQ
Standard
Function
Bus Slot
Card Type
Recommended
Use
0
System Timer
No
-
-
1
Keyboard Controller
No
-
-
2
2nd IRQ Controller
Cascade
No
-
-
8
Real-time Clock
No
-
-
9
Available (appears
as IRQ 2)
Yes
8/16-bit
Network Interface Card
10
Available
Yes
16-bit
USB
11
Available
Yes
16-bit
SCSI Host Adapter
12
Motherboard Mouse
Port Available
Yes
16-bit
Motherboard Mouse Port
13
Math Coprocessor
No
-
-
14
Primary IDE
Yes
16-bit
Primary IDE (Hard disks)
15
Secondary IDE/Available
Yes
16-bit
Secondary IDE (CDROM/Tape)
3
Serial Port 2 (COM2:)
Yes
8/16-bit
COM2:/Internal Modem
4
Serial Port 1 (COM1:)
Yes
8/16-bit
COM1:
5
Sound/Parallel
Port 2 (LPT2:)
Yes
8/16-bit
Sound Card
6
Floppy Disk Controller
Yes
8/16-bit
Floppy Controller
7
Parallel Port 1 (LPT1:)
Yes
8/16-bit
LPT1:
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Notice that interrupts 0, 1, 2, 8, and 13 are not on the bus connectors and are not accessible to
adapter cards. Interrupts 8, 10, 11, 12, 13, 14, and 15 are from the second interrupt controller
and are accessible only by boards that use the 16-bit extension connector, because this is where
these wires are located. IRQ 9 is rewired to the 8-bit slot connector in place of IRQ 2, which
means that IRQ 9 replaces IRQ 2 and, therefore, is available to 8-bit cards, which treat it as
though it were IRQ 2.
Note
Although the 16-bit ISA bus has twice as many interrupts as systems that have the 8-bit ISA bus, you still might run
out of available interrupts, because only 16-bit adapters can use most of the newly available interrupts. Thirtytwo–bit PCI adapters can be mapped to any ISA IRQs.
The extra IRQ lines in a 16-bit ISA system are of little help unless the adapter boards that you
plan to use enable you to configure them for one of the unused IRQs. Some devices are hardwired so that they can use only a particular IRQ. If you have a device that already uses that IRQ,
you must resolve the conflict before installing the second adapter. If neither adapter enables you
to reconfigure its IRQ use, chances are that you cannot use the two devices in the same system.
PCI Interrupts
The PCI bus supports hardware interrupts (IRQs) that can be used by PCI devices to signal to the
bus that they need attention. There are four PCI interrupts called INTA#, INTB#, INTC#, and
INTD#. These INTx# interrupts are level-sensitive, which means that the electrical signaling allows
for them to be shared among PCI cards. In fact, all single device or single function PCI chips or
cards that use only one interrupt must use INTA#. This is one of the rules in the PCI specification. If there are additional devices within a chip or on-board a card, the additional devices can
use INTB# through INTD#. Since there are very few multifunction PCI chips or boards, this
means that practically all the devices on a given PCI bus will be sharing INTA#.
In order for the PCI bus to function in a PC, the PCI interrupts must be mapped to ISA interrupts.
Since ISA interrupts cannot be shared, in most cases each PCI card that is using INTA# on the PCI
bus must be mapped to a different non-sharable ISA interrupt. For example, you could have a system with four PCI slots, and four PCI cards installed each using PCI interrupt INTA#. These cards
would be each mapped to a different available ISA interrupt request (IRQ), such as IRQ9, IRQ10,
IRQ11, and IRQ5 in most cases.
Finding unique IRQs for each device on both the ISA and PCI buses has always been a problem;
there simply aren’t enough free ones to go around. Setting two ISA devices to the same IRQ has
never been possible, but on most newer systems it may be possible to share IRQs between multiple PCI devices. Newer system BIOS as well as plug-and-play operating systems such as Windows
95B (OSR 2) or later, Windows 98, and Windows 2000 all support a function known as PCI IRQ
(interrupt request) Steering. For this to work, both your system BIOS and operating system must
support IRQ Steering. Older system BIOS and Windows 95 or 95a do not have support for PCI
IRQ Steering.
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Normally, the BIOS assigns unique IRQs to PCI devices. If your system supports PCI IRQ Steering,
and it is enabled, Windows assigns IRQs to PCI devices. Even when IRQ Steering is enabled, the
BIOS still initially assigns IRQs to PCI devices. Although Windows has the capability to change
these settings, it generally does not do so automatically, except where necessary to eliminate conflicts. If there are insufficient free IRQs to go around, IRQ Steering allows Windows to assign multiple PCI devices to a single IRQ, thus enabling all the devices in the system to function properly.
Without IRQ Steering, Windows will begin to disable devices once it runs out of free IRQs to
assign.
To determine if your system is using IRQ Steering, you can follow these steps:
1. Click Start, Settings, Control Panel, and then double-click System.
2. Click the Device Manager tab.
3. Double-click the System Devices branch.
4. Double-click PCI Bus, and then click the IRQ Steering tab. There will be a check; it will display IRQ Steering as either Enabled or Disabled. If enabled, it will also specify where the
IRQ table has been read from.
IRQ Steering is controlled by one of four different routing tables that Windows attempts to read.
Windows searches for the tables in order and uses the first one it finds. You cannot control the
order in which Windows searches for these tables, but by selecting or deselecting the “Get IRQ
table using…” check boxes, you can control which table Windows will find first by disabling the
search for specific tables. Windows searches for the following tables:
■ ACPI BIOS table
■ MS Specification table
■ Protected Mode PCIBIOS 2.1 table
■ Real Mode PCIBIOS 2.1 table
Windows first tries to use the ACPI BIOS table to program IRQ Steering, followed by the MS
Specification table, the Protected Mode PCIBIOS 2.1 table, and the Real Mode PCIBIOS 2.1 table.
Windows 95 OSR2 and later versions only offer a choice for selecting the PCIBIOS 2.1 tables via a
single check box, which is by default disabled. Under Windows 98, all IRQ table choices are
selected by default, except the third one, which is the Protected Mode PCIBIOS 2.1 table.
If you are having a problem with a PCI device related to IRQ settings under Windows 95, try
selecting the PCIBIOS 2.1 table and restarting. Under Windows 98, try clearing the ACPI BIOS
table selection and restarting. If the problem persists, try selecting the Protected Mode PCIBIOS
2.1 table and restarting. You should only select “Get IRQ table from Protected Mode PCIBIOS 2.1
call” if a PCI device is not working properly.
If IRQ Steering is shown as disabled in Device Manager, make sure the “Use IRQ Steering” check
box is selected. After selecting this and restarting, if IRQ Steering is still showing as disabled, the
IRQ routing table that must be provided by the BIOS to the operating system may be missing or
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contain errors. Check your BIOS setup to be sure PCI IRQ Steering is enabled. If there is still no
success, you might have to select the “Get IRQ table from Protected Mode PCIBIOS 2.1 call”
check box, or your BIOS does not support PCI bus IRQ Steering. Contact the manufacturer of
your motherboard or BIOS to see if your board or BIOS supports IRQ Steering.
On systems that have support for IRQ Steering, an “IRQ Holder for PCI Steering” might be displayed when you view the System Devices branch of Device Manager. This indicates that an IRQ
has been mapped to PCI and is unavailable for ISA devices, even if no PCI devices are currently
using the IRQ. To view IRQs that are programmed for PCI-mode, follow these steps:
1. Click Start, Settings, Control Panel, and then double-click System.
2. Click the Device Manager tab.
3. Double-click the System Devices branch.
4. Double-click the IRQ Holder for PCI Steering you want to view, and then click the
Resources tab.
I have found this interrupt steering or mapping to be the source of a great deal of confusion.
Even though PCI interrupts (INTx#) can be (and are by default) shared, each card or device that
might be sharing a PCI interrupt must be mapped or steered to a unique ISA IRQ, which in turn
cannot normally be shared. It is only possible to have several PCI devices mapped to the same
ISA IRQ if
■ No ISA devices are using the IRQ.
■ The BIOS and operating system support PCI IRQ Steering.
■ PCI IRQ Steering is enabled.
Without PCI IRQ Steering support, the sharing capabilities of the PCI interrupts are of little benefit, because all PCI to ISA IRQ assignments must then be unique. Without PCI IRQ Steering, you
can easily run out of available ISA interrupts. If IRQ Steering is supported and enabled, multiple
PCI devices will be capable of sharing a single IRQ, allowing for more system expansion without
running out of available IRQs. Better support for IRQ Steering is one of the best reasons for
upgrading to Windows 98, especially if you are using the original OSR1 release of 95.
Another source of confusion is that the interrupt listing shown in the Windows Device Manager
may show the PCI to ISA interrupt mapping as multiple entries for a given ISA interrupt. One
entry would be for the device actually mapped to the interrupt, for example a built-in USB controller, while the other entry for the same IRQ will say IRQ Holder for PCI Steering. This latter
entry, even though claiming to use the same IRQ, does not indicate a resource conflict; instead it
represents the chipset circuitry putting a reservation on that interrupt for mapping purposes. This
is part of the plug-and-play capabilities of PCI and the modern motherboard chipsets.
Note that it is possible to have internal devices on the PCI bus even though all the PCI slots are
free. For example, most systems today have two IDE controllers and a USB controller as devices
on the PCI bus. Normally, the PCI IDE controllers are mapped to ISA interrupts 14 (primary IDE)
and 15 (secondary IDE), while the USB controller can be mapped to the normally available ISA
interrupts 9, 10, 11, or 5.
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◊◊ See “USB (Universal Serial Bus)” p. 892.
The PCI bus allows two types of devices to exist, called bus masters (initiators) or slaves (targets). A
bus master is a device that can take control of the bus and initiate a transfer. The target device is
the intended destination of the transfer. Most PCI devices can act as both masters and targets,
and to be compliant with the PC 97 and newer system design guides, all PCI slots must support
bus master cards.
The PCI bus is an arbitrated bus. This means that a central arbiter (part of the PCI bus controller
in the motherboard chipset) governs all bus transfers, giving fair and controlled access to all the
devices on the bus. Before a master can use the bus, it must first request control from the central
arbiter, and then it is only granted control for a specified maximum number of cycles. This arbitration allows equal and fair access to all the bus master devices, prevents a single device from
hogging the bus, and also prevents deadlocks because of simultaneous multiple device access. In
this manner, the PCI bus acts much like a local area network (LAN), albeit one that is contained
entirely within the system and runs at a much higher speed than conventional external networks
between PCs.
IRQ Conflicts
Perhaps the most common IRQ conflict is the one between the integrated COM2: port found in
most modern motherboards and an internal (card-based) modem. The problem stems from the
fact that true PC card-based modems (not the so-called WinModems, which are software based)
incorporate a serial port as part of the card’s circuitry. This serial port is set as COM2: by default.
Your PC sees this as having two COM2: ports, each using the same IRQ and I/O port address
resources.
The solution to this problem is easy: Enter the system BIOS Setup and disable the built-in COM2:
port in the system. While you are there, you might think about disabling the COM1: port also,
because it is unlikely that you are using it. Disabling unused COMx: ports is one of the best ways
to free up a couple of IRQs for other devices to use.
Another common IRQ conflict involves serial (COM) ports. You may have noticed in the preceding two sections that two IRQs are set aside for two COM ports. IRQ 3 is used for COM2:, and
IRQ 4 is used for COM1:. The problem occurs when you have more than two serial ports in a system. When people add COM3: and COM4: ports, they often don’t set them to non-conflicting
interrupts, and the result is a conflict and the ports don’t work.
Contributing to the problem are poorly designed COM port boards that do not allow IRQ settings
other than 3 or 4. What happens is that they end up setting COM3: to IRQ 4 (sharing it with
COM1:), and COM4: to IRQ 3 (sharing it with COM2:). This is not acceptable, as it will prevent
you from using the two COM ports on any one of the interrupt channels simultaneously. This
was somewhat acceptable under plain DOS, because single-tasking (running only one program at
a time) was the order of the day, but is totally unacceptable with Windows and OS/2. If you must
share IRQs, you can usually get away with sharing devices on the same IRQ as long as they use
different COM ports. For instance, a scanner and an internal modem could share an IRQ,
although if the two devices are used simultaneously, a conflict will result.
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The best solution is to purchase a multiport serial I/O card that will allow non-conflicting interrupt settings, or an intelligent card with its own processor that can handle the multiple ports onboard and only use one interrupt in the system.
◊◊ See “Serial Ports” p. 872.
If a device listed in the table is not present, such as the motherboard mouse port (IRQ 12) or parallel port 2 (IRQ 5), you can consider those interrupts as available. For example, a second parallel
port is a rarity, and most systems will have a sound card installed and set for IRQ 5. Also, on
most systems IRQ 15 is assigned to a secondary IDE controller. If you do not have a second IDE
hard drive, you could disable the secondary IDE controller to free up that IRQ for another device.
Note that an easy way to check your interrupt settings is to use the Device Manager in Windows
95/98, NT, or Windows 2000. By double-clicking on the Computer Properties icon in the Device
Manager, you can get concise lists of all used system resources. Microsoft has also included a program called HWDIAG on Windows 95B and newer versions, which does an excellent job of
reporting system resource usage.
DMA Channels
DMA (Direct Memory Access) channels are used by high-speed communications devices that
must send and receive information at high speed. A serial or parallel port does not use a DMA
channel, but a sound card or SCSI adapter often does. DMA channels sometimes can be shared if
the devices are not the type that would need them simultaneously. For example, you can have a
network adapter and a tape backup adapter sharing DMA channel 1, but you cannot back up
while the network is running. To back up during network operation, you must ensure that each
adapter uses a unique DMA channel.
8-Bit ISA Bus DMA Channels
In the 8-bit ISA bus, four DMA channels support high-speed data transfers between I/O devices
and memory. Three of the channels are available to the expansion slots. Table 4.32 shows the
typical uses of these DMA channels.
Table 4.32
8-Bit ISA Default DMA-Channel Assignments
DMA
Standard Function
Bus Slot
0
Dynamic RAM Refresh
No
1
Available
Yes (8-bit)
2
Floppy disk controller
Yes (8-bit)
3
Hard disk controller
Yes (8-bit)
Because most systems typically have both a floppy and hard disk drive, only one DMA channel is
available in 8-bit ISA systems.
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16-Bit ISA DMA Channels
Since the introduction of the 286 CPU, the ISA bus has supported eight DMA channels, with
seven channels available to the expansion slots. Like the expanded IRQ lines described earlier in
this chapter, the added DMA channels were created by cascading a second DMA controller to the
first one. DMA channel 4 is used to cascade channels 0–3 to the microprocessor. Channels 0–3
are available for 8-bit transfers, and channels 5–7 are for 16-bit transfers only. Table 4.33 shows
the typical uses for the DMA channels.
Table 4.33
16/32-Bit ISA/PCI Default DMA-Channel Assignments
DMA
Standard
Function
Bus
Slot
Card
Type
Transfer
Recommended
Use
0
Available
Yes
16-bit
8-bit
Integrated Sound
1
Available
Yes
8/16-bit
8-bit
8-bit Sound
2
Floppy Disk Controller
Yes
8/16-bit
8-bit
Floppy Controller
3
Available
Yes
8/16-bit
8-bit
LPT1: in ECP Mode
4
1st DMA Controller Cascade
No
-
16-bit
5
Available
Yes
16-bit
16-bit
6
Available
Yes
16-bit
16-bit
ISA SCSI Adapter
7
Available
Yes
16-bit
16-bit
Available
16-bit Sound
Note that PCI adapters don’t use these ISA DMA channels these are only for ISA cards.
The only standard DMA channel used in all systems is DMA 2, which is universally used by the
floppy controller. DMA 4 is not usable and does not appear in the bus slots. DMA channels 1 and
5 are most commonly used by ISA sound cards such as the Sound Blaster 16. These cards use both
an 8- and a 16-bit DMA channel for high-speed transfers.
Note
Although DMA channel 0 appears in a 16-bit slot connector extension and therefore can only be used by a 16-bit
card, it only does 8-bit transfers! Because of this, you will generally not see DMA 0 as a choice on 16-bit cards.
Most 16-bit cards (such as SCSI host adapters) that use DMA channels have their choices limited to DMA 5–7.
EISA
Realizing the shortcomings inherent in the way DMA channels are implemented in the ISA bus,
the creators of the EISA specification created a specific DMA controller for their new bus. They
increased the number of address lines to include the entire address bus, thus allowing transfers
anywhere within the address space of the system. Each DMA channel can be set to run 8-, 16-, or
32-bit transfers. In addition, each DMA channel can be separately programmed to run any of four
types of bus cycles when transferring data:
■ Compatible. This transfer method is included to match the same DMA timing as used in the
ISA bus. This is done for compatibility reasons; all ISA cards can operate in an EISA system
in this transfer mode.
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■ Type A. This transfer type compresses the DMA timing by 25 percent over the Compatible
method. It was designed to run with most (but not all) ISA cards and still yield a speed
increase.
■ Type B. This transfer type compresses timing by 50 percent over the Compatible method.
Using this method, most EISA cards function properly, but only a few ISA cards will be
problem-free.
■ Type C. This transfer method compresses timing by 87.5 percent over the Compatible
method; it is the fastest DMA transfer method available under the EISA specification. No
ISA cards will work using this transfer method.
EISA DMA also allows for special reading and writing operations referred to as scatter write and
gather read. Scattered writes are done by reading a contiguous block of data and writing it to more
than one area of memory at the same time. Gathered reads involve reading from more than one
place in memory and writing to a device. These functions are often referred to as buffered
chaining, and they increase the throughput of DMA operations.
MCA
It might be assumed that because MCA is a complete rebuilding of the PC bus structure that
DMA in an MCA environment would be better constructed. This is not so. Quite the contrary,
DMA in MCA systems were for the most part all designed around one DMA controller with the
following issues:
■ It can only connect to two 8-bit data paths. This can only transfer one or two bytes per bus
cycle.
■ It is only connected to AO:A23 on the address bus. This means it can only make use of the
lower 16MB of memory.
■ Runs at 10MHz.
The incapability of the DMA controller to address more than two bytes per transfer severely cripples this otherwise powerful bus.
I/O Port Addresses
Your computer’s I/O ports enable communications between devices and software in your system.
They are equivalent to two-way radio channels. If you want to talk to your serial port, you need
to know what I/O port (radio channel) it is listening on. Similarly, if you want to receive data
from the serial port, you need to listen on the same channel it is transmitting on.
Unlike IRQs and DMA channels, we have an abundance of I/O ports in our systems. There are
65,535 ports to be exact—numbered from 0000h to FFFFh—and this is an artifact of the Intel
processor design more than anything else. Even though most devices use up to eight ports for
themselves, with that many to spare, we aren’t going to run out anytime soon. The biggest problem you have to worry about is setting two devices to use the same port.
Most modern plug-and-play systems will resolve any port conflicts and select alternative ports for
one of the conflicting devices.
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One confusing issue is that I/O ports are designated by hexadecimal addresses similar to memory
addresses. They are not memory; they are ports. The difference is that when you send data to
memory address 1000h, it gets stored in your SIMM or DIMM memory. If you send data to I/O
port address 1000h, it gets sent out on the bus on that “channel” and anybody listening in
would then “hear” it. If nobody was listening to that port address, the data would reach the end
of the bus and be absorbed by the bus terminating resistors.
Driver programs are primarily what interact with devices at the different port addresses. The driver must know which ports the device is using to work with it, and vice versa. That is not usually
a problem because the driver and device both come from the same company.
Motherboard and chipset devices are normally set to use I/O port addresses from 0h to FFh, and
all other devices use from 100h to FFFFh. Table 4.34 shows the commonly used motherboard and
chipset based I/O port usage:
Table 4.34
Motherboard and Chipset-based Device Port Addresses
Address (hex)
Size
Description
0000 - 000F
16 bytes
Chipset - 8237 DMA 1
0020 - 0021
2 bytes
Chipset - 8259 interrupt controller 1
002E - 002F
2 bytes
Super I/O controller Configuration registers
0040 - 0043
4 bytes
Chipset - Counter/Timer 1
0048 - 004B
4 bytes
Chipset - Counter/Timer 2
0060
1 byte
Keyboard/Mouse controller byte - reset IRQ
0061
1 byte
Chipset - NMI, speaker control
0064
1 byte
Keyboard/Mouse Controller, CMD/STAT Byte
0070, bit 7
1 bit
Chipset - Enable NMI
0070, bits 6:0
7 bits
MC146818 - Real-time clock, Address
0071
1 byte
MC146818 - Real-time clock, Data
0078
1 byte
Reserved - Board configuration
0079
1 byte
Reserved - Board configuration
0080 - 008F
16 bytes
Chipset - DMA page registers
00A0 - 00A1
2 bytes
Chipset - 8259 interrupt controller 2
00B2
1 byte
APM control port
00B3
1 byte
APM status port
00C0 - 00DE
31 bytes
Chipset - 8237 DMA 2
00F0
1 byte
Math Coprocessor Reset Numeric Error
To find out exactly what port addresses are being used on your motherboard, consult the board
documentation or look these settings up in the Windows Device Manager.
Bus-based devices normally use the addresses from 100h on up. Table 4.35 lists the commonly
used bus-based device addresses and some common adapter cards and their settings:
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Bus-based Device Port Addresses
Address (hex)
Size
Description
0130 - 0133
4 bytes
Adaptec SCSI adapter (alternate)
0134 - 0137
4 bytes
Adaptec SCSI adapter (alternate)
0168 - 016F
8 bytes
Fourth IDE interface
0170 - 0177
8 bytes
Secondary IDE interface
01E8 - 01EF
8 bytes
Third IDE interface
01F0 - 01F7
8 bytes
Primary IDE / AT (16-bit) Hard Disk Controller
0200 - 0207
8 bytes
Gameport or Joystick adapter
0210 - 0217
8 bytes
IBM XT expansion chassis
0220 - 0233
20 bytes
Creative Labs Sound Blaster 16 audio (default)
0230 - 0233
4 bytes
Adaptec SCSI adapter (alternate)
0234 - 0237
4 bytes
Adaptec SCSI adapter (alternate)
0238 - 023B
4 bytes
MS bus mouse (alternate)
023C - 023F
4 bytes
MS bus mouse (default)
0240 - 024F
16 bytes
SMC Ethernet adapter (default)
0240 - 0253
20 bytes
Creative Labs Sound Blaster 16 audio (alternate)
0258 - 025F
8 bytes
Intel above board
0260 - 026F
16 bytes
SMC Ethernet adapter (alternate)
0260 - 0273
20 bytes
Creative Labs Sound Blaster 16 audio (alternate)
0270 - 0273
4 bytes
Plug-and-Play I/O read ports
0278 - 027F
8 bytes
Parallel Port 2 (LPT2)
0280 - 028F
16 bytes
SMC Ethernet adapter (alternate)
0280 - 0293
20 bytes
Creative Labs Sound Blaster 16 audio (alternate)
02A0 - 02AF
16 bytes
SMC Ethernet adapter (alternate)
02C0 - 02CF
16 bytes
SMC Ethernet adapter (alternate)
02E0 - 02EF
16 bytes
SMC Ethernet adapter (alternate)
02E8 - 02EF
8 bytes
Serial Port 4 (COM4)
02EC - 02EF
4 bytes
Video, 8514 or ATI standard ports
02F8 - 02FF
8 bytes
Serial Port 2 (COM2)
0300 - 0301
2 bytes
MPU-401 MIDI Port (secondary)
0300 - 030F
16 bytes
SMC Ethernet adapter (alternate)
0320 - 0323
4 bytes
XT (8-bit) hard disk controller
0320 - 032F
16 bytes
SMC Ethernet adapter (alternate)
0330 - 0331
2 bytes
MPU-401 MIDI port (default)
0330 - 0333
4 bytes
Adaptec SCSI adapter (default)
0334 - 0337
4 bytes
Adaptec SCSI adapter (alternate)
0340 - 034F
16 bytes
SMC Ethernet adapter (alternate)
0360 - 036F
16 bytes
SMC Ethernet adapter (alternate)
0366
1 byte
Fourth IDE command port
0367, bits 6:0
7 bits
Fourth IDE status port
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Size
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Description
0370 - 0375
6 bytes
Secondary floppy controller
0376
1 byte
Secondary IDE command port
0377, bit 7
1 bit
Secondary floppy controller Disk Change
0377, bits 6:0
7 bits
Secondary IDE status port
0378 - 037F
8 bytes
Parallel Port 1 (LPT1)
0380 - 038F
16 bytes
SMC Ethernet adapter (alternate)
0388 - 038B
4 bytes
Audio - FM synthesizer
03B0 - 03BB
12 bytes
Video, Mono/EGA/VGA standard ports
03BC - 03BF
4 bytes
Parallel Port 1 (LPT1) in some systems
03BC - 03BF
4 bytes
Parallel Port 3 (LPT3)
03C0 - 03CF
16 bytes
Video, EGA/VGA standard ports
03D0 - 03DF
16 bytes
Video, CGA/EGA/VGA standard ports
03E6
1 byte
Third IDE command port
03E7, bits 6:0
7 bits
Third IDE status port
03E8 - 03EF
8 bytes
Serial Port 3 (COM3)
03F0 - 03F5
6 bytes
Primary floppy controller
03F6
1 byte
Primary IDE command port
03F7, bit 7
1 bit
Primary Floppy controller disk Change
03F7, bits 6:0
7 bits
Primary IDE status port
03F8 - 03FF
8 bytes
Serial Port 1 (COM1)
04D0 - 04D1
2 bytes
Edge/level triggered PCI interrupt controller
0530 - 0537
8 bytes
Windows sound system (default)
0604 - 060B
8 bytes
Windows sound system (alternate)
0678 - 067F
8 bytes
LPT2 in ECP mode
0778 - 077F
8 bytes
LPT1 in ECP mode
0A20 - 0A23
4 bytes
IBM Token-Ring adapter (default)
0A24 - 0A27
4 bytes
IBM Token-Ring adapter (alternate)
0CF8 - 0CFB
4 bytes
PCI Configuration address Registers
0CF9
1 byte
Turbo and Reset control register
0CFC - 0CFF
4 bytes
PCI configuration data registers
FF00 - FF07
8 bytes
IDE bus master registers
FF80 - FF9F
32 bytes
Universal Serial Bus (USB)
FFA0 - FFA7
8 bytes
Primary bus master IDE registers
FFA8 - FFAF
8 bytes
Secondary bus master IDE registers
To find out exactly what your devices are using, again I recommend consulting the documentation for the device or looking the device up in the Windows Device Manager.
Virtually all devices on your system buses use I/O port addresses. Most of these are fairly standardized, meaning you won’t often have conflicts or problems with these settings. In the next
section, you learn more about working with I/O addresses.
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Resolving Resource Conflicts
The resources in a system are limited. Unfortunately, the demands on those resources seem to be
unlimited. As you add more and more adapter cards to your system, you will find that the potential for resource conflicts increases. If your system is fully PnP-compatible, potential conflicts
should be resolved automatically.
How do you know whether you have a resource conflict? Typically, one of the devices in your
system stops working. Resource conflicts can exhibit themselves in other ways, though. Any of
the following events could be diagnosed as a resource conflict:
■ A device transfers data inaccurately.
■ Your system frequently locks up.
■ Your sound card doesn’t sound quite right.
■ Your mouse doesn’t work.
■ Garbage appears on your video screen for no apparent reason.
■ Your printer prints gibberish.
■ You cannot format a floppy disk.
■ The PC starts in Safe mode (Windows 95).
Windows 9x and Windows 2000 will also show conflicts by highlighting a device in yellow or red
in the Device Manager representation. By using the Windows Device Manager, you can usually
spot the conflicts quickly.
In the following sections, you learn some of the steps that you can take to head off resource conflicts or track them down when they occur.
Caution
Be careful in diagnosing resource conflicts; a problem might not be a resource conflict at all, but a computer virus.
Many computer viruses are designed to exhibit themselves as glitches or periodic problems. If you suspect a
resource conflict, it may be worthwhile to run a virus check first to ensure that the system is clean. This procedure
could save you hours of work and frustration.
Resolving Conflicts Manually
Unfortunately, the only way to resolve conflicts manually is to take the cover off your system and
start changing switches or jumper settings on your adapter cards. Each of these changes then
must be accompanied by a system reboot, which implies that they take a great deal of time. This
situation brings us to the first rule of resolving conflicts: When you set about ridding your system
of resource conflicts, make sure that you allow a good deal of uninterrupted time.
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Also make sure that you write down your current system settings before you start making
changes. That way, you will know where you began and can go back to the original configuration
(if necessary).
Finally, dig out the manuals for all your adapter boards; you will need them. If you cannot find
the manuals, contact the manufacturers to determine what the various jumper positions and
switch settings mean. Additionally, you could look for more current information online at the
manufacturers’ Web sites.
Now you are ready to begin your detective work. As you try various switch settings and jumper
positions, keep the following questions in mind; the answers will help you narrow down the conflict areas:
■ When did the conflict first become apparent? If the conflict occurred after you installed a new
adapter card, that new card probably is causing the conflict. If the conflict occurred after
you started using new software, chances are good that the software uses a device that is taxing your system’s resources in a new way.
■ Are there two similar devices in your system that do not work? For example, if your modem,
integrated serial ports, or mouse—devices that use a COM port—do not work, chances are
good that these devices are conflicting with each other.
■ Have other people had the same problem, and if so, how did they resolve it? Public forums—such
as those on CompuServe, Internet newsgroups, and America Online—are great places to
find other users who might be able to help you solve the conflict.
Whenever you make changes in your system, reboot and see whether the problem persists. When
you believe that you have solved the problem, make sure that you test all your software. Fixing
one problem often seems to cause another to crop up. The only way to make sure that all problems are resolved is to test everything in your system.
One of the best pieces of advice I can give you is to try changing one thing at a time, and then
retest. That is the most methodical and simplest way to isolate a problem quickly and efficiently.
As you attempt to resolve your resource conflicts, you should work with and update a systemconfiguration template, as discussed in the following section.
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Using a System-Configuration Template
A system-configuration template is helpful, because it is easier to remember something that is written down than it is to keep it in your head. To create a configuration template, you need to start
writing down what resources are used by which parts of your system. Then, when you need to
make a change or add an adapter, you can quickly determine where conflicts may arise. You can
also use the Windows 95/98 or NT 5.0+ Device Manager to list and print this information.
I like to use a worksheet split into three main areas—one for interrupts, another for DMA channels, and a middle area for devices that do not use interrupts. Each section lists the IRQ or DMA
channel on the left and the I/O port device range on the right. This way, you get the clearest picture of what resources are used and which ones are available in a given system.
Here is the system-configuration template I have developed over the years and still use almost
daily:
This type of configuration sheet is resource-based instead of component-based. Each row in the
template represents a different resource, and lists the component using the resource as well as the
resources used. The chart has pre-entered all the fixed items in a modern PC whose configuration
cannot be changed.
To fill out this type of chart, you would perform the following steps:
1. Enter the default resources used by standard components, such as serial and parallel ports,
disk controllers, and video. You can use the filled out example I have provided to see how
most standard devices are configured.
2. Enter the default resources used by additional add-on components such as sound cards,
SCSI cards, network cards, proprietary cards, and so on.
3. Change any configuration items that are in conflict. Try to leave built-in devices at their
default settings, as well as sound cards. Other installed adapters may have their settings
changed, but be sure to document the changes.
Of course, a template like this is best used when first installing components, not after. Once you
have it completely filled out to match your system, you can label it and keep it with the system.
When you add any more devices, the template will be your guide as to how any new devices
should be configured.
The following example is the same template filled out for a typical modern PC system:
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System Resource Map
PC Make and Model:
_________________________
Serial Number:
_________________________
Date:
_________________________
Interrupts (IRQs):
I/O Port Addresses:
0
-
Timer Circuits ________________________
040-04B ________________
1
-
Keyboard/Mouse Controller ____________
060 & 064 _____________
2
-
2nd 8259 IRQ Controller ______________
0A0-0A1________________
8
-
Real-time Clock/CMOS RAM ___________
070-071________________
9
-
____________________________________
________________________
10 -
____________________________________
________________________
11 -
____________________________________
________________________
12 -
____________________________________
________________________
13 -
Math Coprocessor ____________________
0F0 ____________________
14 -
____________________________________
________________________
15 -
____________________________________
________________________
3
-
____________________________________
________________________
4
-
____________________________________
________________________
5
-
____________________________________
________________________
6
-
____________________________________
________________________
7
-
____________________________________
________________________
Devices not using Interrupts:I/O Port Addresses:
Mono/EGA/VGA Standard Ports _____________
3B0-3BB ________________
EGA/VGA Standard Ports____________________
3C0-3CF________________
CGA/EGA/VGA Standard Ports ______________
3D0-3DF ________________
__________________________________________
________________________
__________________________________________
________________________
__________________________________________
________________________
__________________________________________
________________________
__________________________________________
________________________
DMA Channels:
0
-
____________________________________
1
-
____________________________________
2
-
____________________________________
3
-
____________________________________
4
-
DMA Channel 0-3 Cascade ____________
5
-
____________________________________
6
-
____________________________________
7
-
____________________________________
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System Resource Map
PC Make and Model:
Intel SE440BX-2 __________
Serial Number:
100000 ________________
Date:
06/09/99______________
Interrupts (IRQs): I/O Port Addresses:
0
-
Timer Circuits ________________________
040-04B ________________
1
-
Keyboard/Mouse Controller ____________
060 & 064 _____________
2
-
2nd 8259 IRQ Controller ______________
0A0-0A1________________
8
-
Real-time Clock/CMOS RAM ___________
070-071________________
9
-
SMC EtherEZ Ethernet card _____________
340-35F ________________
10 -
____________________________________
________________________
11 -
Adaptec 1542CF SCSI Adapter (scanner)
334-337* ______________
12 -
Motherboard Mouse Port_______________
060 & 064 _____________
13 -
Math Coprocessor ____________________
0F0 ____________________
14 -
Primary IDE (hard disk 1 and 2) _________
1F0-1F7, 3F6 ____________
15 -
Secondary IDE (CD-ROM/tape) _________
170-177, 376___________
3
-
Serial Port 2 (Modem) _________________
3F8-3FF _________________
4
-
Serial Port 1 (COM1) _________________
2F8-2FF _________________
5
-
Sound Blaster 16 Audio _______________
220-233________________
6
-
Floppy Controller _____________________
3F0-3F5 ________________
7
-
Parallel Port 1 (Printer) _________________
378-37F ________________
Devices not using interrupts:
I/O Port Addresses:
Mono/EGA/VGA Standard Ports _____________
3B0-3BB ________________
EGA/VGA Standard Ports____________________
3C0-3CF________________
CGA/EGA/VGA Standard Ports ______________
3D0-3DF ________________
ATI Mach 64 video card additional ports _______
102,1CE-1CF,2EC-2EF ____
Sound Blaster 16 MIDI port___________________
330-331________________
Sound Blaster 16 Game port (joystick)__________
200-207________________
Sound Blaster 16 FM synthesizer (music) ________
388-38B ________________
__________________________________________
________________________
DMA Channels:
0
- ____________________________________
1
-
Sound Blaster 16 (8-bit DMA) ___________
2
-
Floppy Controller _____________________
3
-
Parallel Port 1 (in ECP mode) ___________
4
-
DMA Channel 0-3 Cascade ____________
5
-
Sound Blaster 16 (16-bit DMA) _________
6
-
Adaptec 1542CF SCSI adapter* _______
7
-
____________________________________
*Represents a resource setting that had to be changed to resolve a conflict.
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As you can see from this template, only one IRQ and two DMA channels remain available, and
that would be no IRQs if I enable the USB on the motherboard! As you can see, interrupt shortages are a big problem in modern systems. In that case I would probably find a way to recover
one of the other interrupts, for example I am not really using COM1, so I could disable that port
and gain back IRQ 4. In this sample configuration, the primary and secondary IDE connectors
were built into the motherboard:
■ Floppy controller
■ Two serial ports
■ One parallel port
Whether these devices are built into the motherboard or on a separate card makes no difference
because the resource allocations are the same in either case. All default settings are normally used
for these devices, and are indicated in the completed configuration. Next, the accessory cards
were configured. In this example, the following cards were installed:
■ SVGA video card (ATI Mach 64)
■ Sound card (Creative Labs Sound Blaster 16)
■ SCSI host adapter (Adaptec AHA-1542CF)
■ Network interface card (SMC EtherEZ)
It helps to install the cards in this order. Start with the video card; next, add the sound card. Due
to problems with software that must be configured to the sound card, it is best to install it early
and make sure only default settings are used. It is better to change settings on other cards than
the sound card.
After the sound card, the SCSI adapter was installed; however, the default I/O port addresses (330331) and DMA channel (DMA 5) used were in conflict with other cards (mainly the sound card).
These settings were changed to their next logical settings that did not cause a conflict.
Finally, the network card was installed, which also had default settings that conflicted with other
cards. In this case, the Ethernet card came preconfigured to IRQ 3, which was already in use by
COM2:. The solution was to change the setting, and IRQ 9 was the next logical choice in the
card’s configuration settings.
Even though this is a fully loaded configuration, only three individual items among all the cards
had to be changed to achieve an optimum system configuration. As you can see, using a configuration template like the one shown can make what would otherwise be a jumble of settings lay
out in an easy-to-follow manner. The only real problems you will run into once you work with
these templates are cards that do not allow for enough adjustment in their settings, or cards
which are lacking in documentation. As you can imagine, you will need the documentation for
each adapter card, as well as the motherboard, in order to accurately complete a configuration
table like the one shown.
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Tip
Do not rely too much on third-party software diagnostics such as MSD.EXE, which claim to be capable of showing
hardware settings such as IRQ and I/O port settings. While they can be helpful in certain situations, they are often
wrong with respect to at least some of the information they are displaying about your system. One or two items
shown incorrectly can be very troublesome if you believe the incorrect information and configure your system based
on it!
A much better utility to view these settings is the Device Manager built-in to Windows 95/98 and Windows NT
and Windows 2000. On a plug-and-play system, it will not only report settings, but allow you to change them.
On older legacy hardware, you will be able to view the settings but not change them. To change the settings of
legacy (non-plug and play) hardware, you’ll have to manually move jumpers or switches and run the special configuration software that came with the card. Consult the card manufacturer or documentation for more information.
Heading Off Problems: Special Boards
A number of devices that you might want to install in a computer system require IRQ lines or
DMA channels, which means that a world of conflict could be waiting in the box that the device
comes in. As mentioned in the preceding section, you can save yourself problems if you use a system-configuration template to keep track of the way that your system is configured.
You also can save yourself trouble by carefully reading the documentation for a new adapter
board before you attempt to install it. The documentation details the IRQ lines that the board
can use as well as its DMA-channel requirements. In addition, the documentation will detail the
adapter’s upper-memory needs for ROM and adapter.
The following sections describe some of the conflicts that you may encounter when you install
today’s most popular adapter boards. Although the list of adapter boards covered in these sections is far from comprehensive, the sections serve as a guide to installing complex hardware
with minimum hassle. Included are tips on soundboards, SCSI host adapters, and network
adapters.
Soundboards
Sound cards are probably the biggest single resource hog in your system. They usually use at least
one IRQ, two DMA channels, and multiple I/O port address ranges. This is because a sound card
is actually several different pieces of hardware all on one board. Most sound cards are similar to
the Sound Blaster 16 from Creative Labs.
Figure 4.52 shows the default resources used by the components on a typical Sound Blaster 16
card.
As you can see, these cards use quite a few resources. If you take the time to read your soundboard’s documentation and determine its communications-channel needs, compare those needs
to the IRQ lines and DMA channels that already are in use in your system, and then change the
settings of the other adapters to avoid conflicts with the sound card, your installation will go
quickly and smoothly.
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Figure 4.52
Device
Interrupt
I/O Ports
16-bit DMA
8-bit DMA
Audio
IRQ5
220h-233h
DMA 5
DMA 1
Device
Interrupt
MIDI Port
FM Synthesizer
Game Port
330h-331h
388h-38Bh
200h-207h
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Default resources for Sound Blaster 16 card.
Tip
The greatest single piece of advice I can give you for installing a sound card is to put the sound card in before all
other cards—except for video. In other words, let the sound card retain all its default settings; never change a
resource setting to prevent a conflict. Instead, always change the settings of other adapters when a conflict with the
sound card arises. The problem here is that many educational and game programs that use sound are very poorly
written with respect to supporting alternative resource settings on sound cards. Save yourself some grief, and let the
sound card have its way!
One example of a potential soundboard conflict is the combination of a Sound Blaster 16 and an
Adaptec SCSI adapter. The Sound and SCSI adapters will conflict on DMA 5 as well as on I/O
ports 330-331. Rather than changing the settings of the sound card, it is best to alter the SCSI
adapter to the next available settings that will not conflict with the sound card or anything else.
The final settings are shown in the previous configuration template.
The cards in question (Sound Blaster 16 and AHA-1542CF) are not singled out here because there
is something wrong with them, but instead because they happen to be the most popular cards of
their respective types, and as such will often be paired together.
Most people would be using PCI versions of these cards today, but they will still require the same
types of resource settings with the only exception being DMA channels. Unfortunately it wasn’t
DMA channels that we were really running out of! The interrupt shortage continues even with
PCI cards because they must be mapped to ISA IRQs. The real solution will be in a year or so
when we start to see a new breed of PC that lacks any ISA slots and which breaks ties with that
bus forever. When that happens, we will be free of the interrupt restrictions we have been on for
so many years.
Tip
The newer PCI sound cards are largely incompatible with older DOS-based software because they don’t use DMA
channels like their ISA counterparts. Either update your software to 32-bit Windows versions or you won’t be able
to use these newer PCI bus sound cards. Most of the newer PCI cards do include an emulation program that
allows the card to work with older DMA dependent software, but the results are often problematic.
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SCSI Adapter Boards
SCSI adapter boards use more resources than just about any other type of add-in device except
perhaps a sound card. They will often use resources that are in conflict with sound cards or network cards. A typical SCSI host adapter requires an IRQ line, a DMA channel, a range of I/O port
addresses, plus a 16KB range of unused upper memory for its ROM and possible scratch-pad RAM
use. Fortunately, the typical SCSI adapter is also easy to reconfigure, and changing any of these
settings should not affect performance or software operation.
Before installing a SCSI adapter, be sure to read the documentation for the card, and make sure
that any IRQ lines, DMA channels, I/O ports, and upper memory that the card needs are available. If the system resources that the card needs are already in use, use your system-configuration
template to determine how you can alter the settings on the SCSI card or other cards to prevent
any resource conflicts before you attempt to plug in the adapter card.
Network Interface Cards (NICs)
Networks are becoming more and more popular all the time. A typical network adapter does not
require as many resources as some of the other cards discussed here, but will require at least a
range of I/O port addresses and an interrupt. Most NICs will also require a 16KB range of free
upper memory to be used for the RAM transfer buffer on the network card. As with any other
cards, make sure that all these resources are unique to the card and are not shared with any other
devices.
Multiple-COM-Port Adapters
A serial port adapter usually has two or more ports on-board. These COM ports require an interrupt and a range of I/O ports each. There aren’t too many problems with the I/O port addresses,
because the ranges used by up to four COM ports in a system are fairly well defined. The real
problem is with the interrupts. Most older installations of more than two serial ports have any
additional ones sharing the same interrupts as the first two. This is incorrect, and will cause nothing but problems with software that runs under Windows or OS/2. With these older boards, make
sure that each serial port in your system has a unique I/O port address range, and more importantly, a unique interrupt setting.
Because COM ports are required for so many peripherals that connect to the modern PC, and
because the number of COM ports that can be used is strictly limited by the IRQ setup in the
basic IBM system design, special COM-port cards are available that enable you to assign a unique
IRQ to each of the COM ports on the card. For example, you can use such a card to leave COM1:
and COM2: configured for IRQ 4 and IRQ 3, respectively, but to configure COM3: for IRQ 10 and
COM4: for IRQ 12 (provided you do not have a motherboard-based mouse port in your system).
Many newer multiport adapter cards—such as those offered by Byte Runner Technologies—allow
“intelligent” interrupt sharing among ports. In some cases, you can have up to 12 COM port settings without conflict problems. Check with your adapter card’s manufacturer to determine if it
allows for automatic or “intelligent” interrupt sharing.
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Although most people have problems incorrectly trying to share interrupts when installing more
than two serial ports in a system, there is a fairly common problem with the I/O port addressing
that should be mentioned. Many of the high-performance video chipsets, such as those from S3
Inc. and ATI, use some additional I/O port addresses that will conflict with the standard I/O port
addresses used by COM4:.
In the example system-configuration just covered, you can see that the ATI video card uses some
additional I/O port addresses, specifically 2EC-2EF. This is a problem because COM4: is normally
configured as 2E8-2EF, which overlaps with the video card. The video cards that use these
addresses are not normally adjustable for this setting, so you will either have to change the
address of COM4: to a nonstandard setting or disable COM4: and restrict yourself to using only
three serial ports in the system. If you do have a serial adapter that supports nonstandard I/O
address settings for the serial ports, you must ensure that those settings are not used by other
cards, and you must inform any software or drivers, such as those in Windows, of your nonstandard settings.
With a multiple-COM-port adapter card installed and properly configured for your system, you
can have devices hooked to numerous COM ports, and up to four devices can be functioning at
the same time. For example, you can use a mouse, modem, plotter, and serial printer at the same
time.
USB (Universal Serial Bus)
USB ports are now found on most motherboards, and with Windows 98 we finally have an operating system that will properly support them. One problem is that USB will take another interrupt from your system, and many computers either don’t have any free or are down to their last
one. If your system supports PCI IRQ Steering, this shouldn’t be much of a problem because IRQ
should be sharable with other PCI devices. If you are out of interrupts, you should look at what
other devices you can disable (such as COM or LPT ports) in order to gain back a necessary interrupt for other devices.
The big advantage of USB from an IRQ or resource perspective is that the USB bus uses only one
IRQ no matter how many devices (up to 127) are attached. This means you can freely add or
remove devices from the USB without worrying about running out of resources or having
resource conflicts.
If you aren’t using any USB devices, you should turn off the port using your motherboard CMOS
setup so that the IRQ it was using will be freed. In the future, as we move to USB-based keyboards, mice, modems, printers, etc., the IRQ shortage will be less of a problem. Also the elimination of the ISA bus in our systems will go a long way to solve this problem as well.
Miscellaneous Boards
Some video cards ship with advanced software that allows special video features such as oversized
desktops, custom monitors, switch modes on-the-fly, and so on. Unfortunately this software
requires that the card be configured to use an interrupt. I suggest you dispense with this unnecessary software and configure the card to free up the interrupt for other devices.
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Also related to video is the use of an MPEG decoder add-on card that works in addition to your
normal graphics adapter. These are used more in specialized video production, editing, and in
playing DVD movies, however, they do use additional system resources which must be available.
Plug-and-Play Systems
Plug and Play (PnP) represents a major revolution in recent interface technology. PnP first came
on the market in 1995, and most new systems come ready to take advantage of it. In the past, PC
users have been forced to muddle through a nightmare of dip switches and jumpers every time
they wanted to add new devices to their systems. The results, all too often, were system resource
conflicts and non-functioning cards.
PnP is not an entirely new concept. It was a key design feature of MCA and EISA interfaces, but
the limited appeal of MCA and EISA meant that they never became industry standards. Therefore,
mainstream PC users still worry about I/O addresses, DMA channels, and IRQ settings. But now
that PnP specifications are available for ISA-, PCI-, SCSI-, IDE-, and PCMCIA-based systems,
worry-free hardware setup is within the grasp of all new computer buyers.
Of course, PnP may well be within your grasp, but that does not necessarily mean you are ready
to take advantage of it. For PnP to work, the following components are required:
■ PnP hardware
■ PnP BIOS
■ PnP operating system (optional)
Each of these components needs to be PnP-compatible, meaning that it complies with the PnP
specifications. The Plug-and-Play BIOS is covered in Chapter 5.
The Hardware Component
The hardware component refers to both computer systems and adapter cards. The term does not
mean, however, that you cannot use your older ISA adapter cards (referred to as legacy cards) in a
PnP system. You can use these cards; in fact, your PnP BIOS automatically reassigns PnP-compatible cards around existing legacy components.
PnP adapter cards communicate with the system BIOS and the operating system to convey information about what system resources are needed. The BIOS and operating system, in turn, resolve
conflicts (wherever possible) and inform the adapter cards which specific resources it should use.
The adapter card then can modify its configuration to use the specified resources.
The BIOS Component
The BIOS component means that most users of older PCs need to update their BIOSes or purchase new machines that have PnP BIOSes. For a BIOS to be compatible, it must support 13 additional system function calls, which can be used by the OS component of a PnP system. The PnP
BIOS specification was developed jointly by Compaq, Intel, and Phoenix Technologies.
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The PnP features of the BIOS are implemented through an expanded POST. The BIOS is responsible for identification, isolation, and possible configuration of PnP adapter cards. The BIOS accomplishes these tasks by performing the following steps:
1. Disables any configurable devices on the motherboard or on adapter cards.
2. Identifies any PnP PCI or ISA devices.
3. Compiles an initial resource-allocation map for ports, IRQs, DMAs, and memory.
4. Enables I/O devices.
5. Scans the ROMs of ISA devices.
6. Configures initial program-load (IPL) devices, which are used later to boot the system.
7. Enables configurable devices by informing them which resources have been assigned to
them.
8. Starts the bootstrap loader.
9. Transfers control to the operating system.
The Operating System Component
The operating system component can be implemented by most newer systems, such as OS/2,
Windows 95, Windows 98, or DOS extensions. Extensions of this type should be familiar to most
DOS users; extensions have been used for years to provide support for CD-ROM drives. Extension
software is available now for existing operating systems, and you can expect all new PC operating
systems to have PnP support built in. If you are using Windows NT 4.0, PnP drivers may have
been loaded automatically. If not, the driver can be found on the Windows NT 4.0 CD in the
DRVLIB\PNPISA\ directory. Open the correct subdirectory for your chipset and install the file
PNPISA.INF. Windows 2000 has full support for PnP built-in.
It is the responsibility of the operating system to inform users of conflicts that cannot be resolved
by the BIOS. Depending on the sophistication of the operating system, the user then could configure the offending cards manually (onscreen) or turn the system off and set switches on the
physical cards. When the system is restarted, the system is checked for remaining (or new) conflicts, any of which are brought to the user’s attention. Through this repetitive process, all system
conflicts are resolved.
Note
Plug and Play is still going through some revisions. Windows 95 requires at least version 1.0a of the ISA PnP
BIOS. If your system does not have the most current BIOS, I suggest you install a BIOS upgrade. With the Flash
ROM used in most PnP systems, you can download the new BIOS image from the system vendor or manufacturer
and run the supplied BIOS update program.
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Knowing What to Look For (Selection
Criteria)
As a consultant, I am often asked to make a recommendation for purchases. Making these types
of recommendations is one of the most frequent tasks a consultant performs. Many consultants
charge a large fee for this advice. Without guidance, many individuals don’t have any rhyme or
reason to their selections and instead base their choices solely on magazine reviews or, even
worse, on some personal bias. To help eliminate this haphazard selection process, I have developed a simple checklist that will help you select a system. This list takes into consideration several important system aspects overlooked by most checklists. The goal is to ensure that the
selected system truly is compatible and has a long life of service and upgrades ahead.
It helps to think like an engineer when you make your selection. Consider every aspect and detail
of the motherboards in question. For instance, you should consider any future uses and upgrades.
Technical support at a professional (as opposed to a user) level is extremely important. What support will be provided? Is there documentation, and does it cover everything else?
In short, a checklist is a good idea. Here is one for you to use in evaluating any PC-compatible
system. You might not have to meet every one of these criteria to consider a particular system,
but if you miss more than a few, consider staying away from that system. The items at the top of
the list are the most important, and the items at the bottom are perhaps of lesser importance
(although I think each item is important). The rest of this chapter discusses in detail the criteria
in this checklist:
■ Processor. A modern Pentium-class motherboard should use as a minimum the Pentium
MMX processor, which requires a Socket 7 type socket for the processor to plug into. Even
better would be a board incorporating the 100MHz Super-7 standard developed by AMD
and Cyrix for their newest Socket 7 processors such as the AMD K6-3. There should also be
a built-in adjustable voltage regulator allowing for different voltage CPUs to be accommodated without purchasing an additional regulator module. For even more performance, I
recommend a motherboard that supports the Slot 1 or Socket 370 design. Slot 1 boards will
allow you to use any Celeron, Pentium II, or Pentium III processor and are the most powerful and flexible boards around. Socket 370 boards can only use the socketed Celeron
processors for now and are good for lower end systems.
The lowest cost PII/III class processor is the Celeron introduced by Intel in mid-1998. This
is a PII processor originally without the level 2 cache, but later incorporating a full-core
speed L2 cache that actually makes it faster than a regular Pentium II for much less cost.
The Celeron has turned out to be a real performance bargain because of this improved L2
cache design, where the cache is integrated directly on the processor die. All Pentium Pro
motherboards use Socket 8, and all non-server Pentium II/III systems use Slot 1 in which to
install the processor.
■ Processor Sockets. A Pentium motherboard should have at least one ZIF socket that follows
the Intel Socket 7 (321-pin) specification. The Socket 7 with a built-in VRM (Voltage
Regulator Module) rather than a socket for one that plugs in is best. This is because if you
change the processor later, the built-in VRM can be reconfigured with jumpers, while if you
have only a VRM socket, you will have to purchase a new VRM to go with each new voltage processor you try.
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Pentium Pro (P6) motherboards use Socket 8, and many are set up for multiple processors.
Pentium II/III boards use either Slot 1 or Slot 2. The Slot 1 systems are for normal use,
while Slot 2 systems are only for the higher end Pentium II/III Xeon server processors.
There are Slot 1 and Slot 2 boards available with multiple processor sockets. Before going to
the expense of buying a multiprocessor board, ensure that your operating system is capable
of handling it. For instance, while Windows 95 or 98 cannot really benefit from more than
one CPU, Windows NT/2000, OS/2, and some others may run considerably faster.
■ Motherboard Speed. A Pentium or Pentium Pro motherboard should run at 66MHz minimum, some can be set to an overclocked (but often fully functional) speed of 75MHz.
Pentium II/III motherboards are available to run at either 66MHz or 100MHz, and up to
133MHz for the newer boards. Notice that all the Pentium processors sold today run at a
multiple of the motherboard speed. For example, the Pentium II 350, 400, and higher
megahertz processors run at a motherboard speed of 100MHz, and would therefore require
a motherboard capable of 100MHz operation. Pentium 333MHz and lower speed processors
run at 66MHz maximum. Currently all the Celeron processors are intended to run at the
66MHz board speed. All components on the motherboard (especially cache memory on
Pentium boards) should be rated to run at the maximum allowable motherboard speed.
■ Cache Memory. All classic Pentium motherboards should have 256–512KB of L2 cache onboard, better ones will have 1MB or even 2MB. P6 processors such as the Pentium Pro,
Pentium II/III, and Celeron use a built-in L1/L2 cache, which means that there will be no
cache on a P6 motherboard. The Pentium Pro can have 256KB, 512KB, or 1MB of Level 2
cache built-in. The Pentium II/III can have either 128KB (Celeron) or 512KB, and 1MB or
more in the Xeon processors. The Level 2 cache on a classic Pentium board should be populated with chips that are fast enough to support the maximum motherboard speed, which
should be 15ns or faster for 66MHz maximum motherboard speeds, and 13ns or better for
75MHz operation. For Pentium boards, the cache should be a Synchronous SRAM (Static
RAM) type, which is also called Pipelined Burst SRAM.
■ SIMM/DIMM Memory. If the board is being used to upgrade an older system which used 72pin SIMMs, it may be desirable to get the type that has both SIMM and DIMM sockets. If
you are getting all new memory for the board (recommended), I highly recommend only
using boards which take SDRAM (Synchronous DRAM) 168-pin DIMMs (Dual In-line
Memory Modules). Due to the 64-bit design of these boards, the 72-pin SIMMs must be
installed in matched pairs, while DIMMs are installed one at a time (one per 64-bit bank).
Be sure that the memory is compatible with the chipset you are using, and more specifically is rated for the 66MHz or 100MHz speed it will be running. Carefully consider the
total amount of memory you will need, and how much the board supports. Classic
Pentium systems with the 430FX, VX, or TX chipset only support a maximum of 64MB of
cacheable memory, which effectively limits you to that amount. Pentium II systems will
allow caching for all the memory you can fit into the board, and most will handle 384MB
or more of SDRAM DIMM memory. The 333MHz and lower Pentium II processors can
cache up to 512MB of RAM (note most motherboards won’t handle that much) whereas
the newer 350MHz and faster Pentium IIs will cache up to 4GB of system RAM! While
32MB is regarded as a minimum for today’s memory hungry applications, you might actually require much more. I recommend installing 64MB in most new systems. For maximum
performance, look for systems that support 3.3v SDRAM (Synchronous DRAM) as a minimum. Future systems will use even faster RDRAM (Rambus DRAM) RIMMs (Rambus Inline
Memory Modules) with speeds of 800MHz or more!
Mission-critical systems should use parity or ECC (Error Correcting Code) DIMMs and
ensure that the motherboard fully supports ECC operation. Most Pentium (430 series)
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chipsets do not support ECC, while most Pentium II chipsets do. Note that the low-end
440EX boards normally used in Celeron processor-based systems do not support ECC and
should not be used for mission-critical applications.
Finally, note that most Pentium and Pentium II motherboards support either 3 or 4 DIMM
sockets. Be sure that you populate them wisely so you don’t have to resort to removing
memory later to add more, which is not very cost-effective.
■ Bus Type. Pentium, Pentium Pro, and Pentium II motherboards should have one or more
ISA bus slots and at least three or four PCI local bus slots. Make sure the PCI slots conform
to the PCI 2.1 revision (primarily based on the chipset). Take a look at the layout of the
slots to ensure that cards inserted in them will not block access to memory sockets or be
blocked by other components in the case. Newer systems should also feature one AGP
(Accelerated Graphics Port) slot for a high performance AGP video card.
■ BIOS. The motherboard should use an industry standard BIOS such as those from AMI,
Phoenix, or Award. The BIOS should be of a Flash ROM or EEPROM (Electrically Erasable
Programmable Read Only Memory) design for easy updating. Look for a BIOS Recover
jumper or mode setting, as well as possibly a Flash ROM write-protect jumper on some systems. The BIOS should support the Plug-and-Play (PnP) specification and Enhanced IDE or
Fast ATA hard drives. There should also be support for the newer LS-120 (120M) floppy drives as well as IDE CD-ROM drives as boot devices. APM (Advanced Power Management)
support should be built into the BIOS as well.
■ Form Factor. For maximum flexibility, performance, reliability, and ease-of-use, the ATX
form factor cannot be beat. ATX has several distinct performance and functional advantages over Baby-AT, and is vastly superior to any proprietary designs such as LPX.
Additionally, the new NLX form factor might be a consideration for low profile or low cost
desktop systems.
■ Built-in interfaces. Ideally, a motherboard should contain as many built-in standard controllers and interfaces as possible (except perhaps video). A motherboard should have a
built-in floppy controller, built-in primary and secondary local bus (PCI or VL-Bus),
Enhanced IDE (also called Fast ATA) connectors, two built-in, high-speed serial ports (must
use 16550A type buffered UARTs), two built-in USB (Universal Serial Bus) ports, and a builtin high speed parallel port (must be EPP/ECP-compliant). A built-in PS/2 type (6-pin miniDIN) mouse port should be included as well.
The USB ports have taken awhile to catch on, but they will become a “must-have” in the
near future as more and more USB peripherals become available. A built-in SCSI port is a
bonus as long as it conforms to ASPI (Advanced SCSI Programming Interface) standards.
Built-in network adapters are also nice as long as they are the type that matches your network needs. A built-in sound card is a great feature, usually offering full Sound Blaster compatibility and functions, possibly offering additional features as well. If your sound needs
are more demanding, you may find the built-in solutions less desirable, and want to have a
separate sound card in your system. Built-in video adapters are also a bonus in some situations, but because there are many different video chipset and adapter designs to choose
from, generally there are better choices in external local bus video adapters. This is especially true if you need the highest performance video available.
Normally built-in devices can be disabled to allow future add-ons, but there can be problems.
■ Plug and Play (PnP). The motherboard and BIOS should fully support the Intel PnP specification. This will allow automatic configuration of PCI adapters as well as PnP ISA adapters.
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Tip
Even if a motherboard doesn’t list that it’s PnP-compatible, it may be. PCI motherboards are required to be PnP-compatible, as it is a part of the PCI standard.
■ Power Management. The motherboard should fully support SL Enhanced processors with
APM (Advanced Power Management) and SMM (System Management Mode) protocols that
allow for powering down various system components to different levels of readiness and
power consumption. The latest standards for power management are called ACPI
(Advanced Configuration & Power Interface) version 1.0; make sure any new board you
purchase supports that as a minimum. An Energy-Star compliant system is also a bonus
because it will use less than 30 watts of electrical energy when in Sleep mode, saving
energy as well as your electric bill.
■ Motherboard chipset. Pentium II motherboards should use a high performance chipset that
supports SDRAM DIMMs—preferably one that allows ECC memory as well, such as the
Intel 440LX or 440BX. The 440EX, which is designed for low cost and low-end systems
only, does not support ECC memory and should not be used in mission-critical systems.
Note that for classic Pentium systems, most of the available Intel chipsets do not support
parity or ECC memory. In that case, boards with chipsets from ALi (Acer Laboratories Inc.),
VIA technologies or SiS (Silicon integrated Systems) should be considered. These companies
have continued making high performance, classic Pentium chipsets, and many of their
offerings do support SDRAM DIMMs with ECC.
■ Documentation. Good technical documentation is a requirement. Documents should include
information on any and all jumpers and switches found on the board; connector pinouts
for all connectors; specifications for cache RAM chips, SIMMs, and other plug-in components; and any other applicable technical information. I would also acquire separate documentation from the BIOS manufacturer covering the specific BIOS used in the system, as
well as the data books covering the specific chipset used in the motherboard. Additional
data books for any other controller or I/O chips on-board are a bonus, and can be acquired
from the respective chip manufacturers.
Another nice thing to have is available online support and documentation updates,
although this should not be accepted in place of good hardcopy manuals.
You may notice that these selection criteria seem fairly strict, and may disqualify many motherboards on the market, including what you already have in your system! These criteria will, however, guarantee you the highest quality motherboard offering the latest in PC technology that
will be upgradable, expandable, and provide good service for many years.
Most of the time I recommend purchasing boards from better-known motherboard manufacturers
such as Intel, Acer, ABIT, AsusTek, Elitegroup, FIC (First International Computer), and others.
These boards might cost a little more, but there is some safety in the more well-known brands.
That is, the more boards that they sell, the more likely that any problems will have been discovered by others and solved long before you get yours. Also, if service or support is needed, the
larger vendors are more likely to be around in the long run.
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Documentation
As mentioned, extensive documentation is an important factor to consider when you’re planning
to purchase a motherboard. Most motherboard manufacturers design their boards around a particular chipset, which actually counts as the bulk of the motherboard circuitry. There are a number of manufacturers offering chipsets, such as Intel, VIA, ALi, SiS, and others. I recommend
obtaining the data book or other technical documentation on the chipset directly from the
chipset manufacturer.
One of the more common questions I hear about a system relates to the BIOS Setup program.
People want to know what the “Advanced Chipset Setup” features mean and what will the effects
of changing them be. Often they go to the BIOS manufacturer thinking that the BIOS documentation will offer help. Usually, however, people find that there is no real coverage of what the
chipset setup features are in the BIOS documentation. You will find this information in the data
book provided by the chipset manufacturer. Although these books are meant to be read by the
engineers who design the boards, they contain all the detailed information about the chipset’s
features, especially those that might be adjustable. With the chipset data book, you will have an
explanation of all the controls in the Advanced Chipset Setup section of the BIOS Setup program.
Besides the main chipset data books, I also recommend collecting any data books on the other
major chips in the system. This would include any floppy or IDE controller chips, Super I/O
chips, and of course the main processor. You will find an incredible amount of information on
these components in the data books.
Caution
Most chipset manufacturers only make a particular chip for a short time, rapidly superseding it with an improved or
changed version. The data books are only available during the time the chip is being manufactured, so if you wait
too long, you will find that such documents may no longer be available. The time to collect documentation on your
motherboard is now!
Using Correct Speed-Rated Parts
Some vendors use substandard parts in their systems to save money. Because the CPU is one of
the most expensive components on the motherboard, and motherboards are sold to system
assemblers without the CPU installed, it is tempting for the assembler to install a CPU rated for
less than the actual operating speed. A system could be sold as a 266MHz system, for example,
but when you look “under the hood,” you may find a CPU rated for only 233MHz. This is called
overclocking, and many vendors have practiced this over the last few years. Some even go so far as
to remark the CPUs, so that even if you look, the part appears to have the correct rating. The
only way to stop that is to purchase systems from known, reliable vendors, and purchase processors from distributors that are closely connected with the manufacturer. Overclocking is fine if
you want to do it yourself and understand the risks, but when I purchase a new system, I expect
that all the parts included be rated to run at the speed they are set to.
√√ See “Processor Speed Ratings” p. 42.
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When a chip is run at a speed higher than it is rated for, it will run hotter than it would normally. This can cause the chip to overheat occasionally, which would appear as random lockups,
glitches, and frustration. I highly recommend that you check to be sure you are getting the right
speed-rated parts you are paying for.
Also make sure you use the recommended heat sink compound (thermal grease). This can
improve the efficiency of your heat sink by up to 30 percent.
This practice is easy to fall into because the faster rated chips cost more money. Intel and other
chip manufacturers usually rate their chips very conservatively. Over the years I have taken several 25MHz 486 processors and run them at 33MHz, and they seemed to work fine. The Pentium
166 and even some 133 chips I have seem to run fine at 200MHz. Although I might purchase a
Pentium 166 system and make a decision to run it at 200MHz, if I were to experience lockups or
glitches in operation, I would immediately return it to 166MHz and retest. If I purchase a
200MHz system from a vendor, I fully expect it to have 200MHz parts, not 166mHz parts running past their rated speed! These days, many chips will have some form of heat sink on them,
which helps to prevent overheating, but which can also sometimes cover up for a “pushed” chip.
Fortunately since the Pentium processor, Intel has been marking all their chips on the bottom as
well as the top.
The practice of overclocking may be all but over for Intel processor systems. Intel has recently
began building overclock protection into their CPUs, which prevents them from running at any
speed higher than they are rated at. They will run at lower speeds, but not higher ones. This was
done mainly to combat remarking CPUs and deceiving customers, although unfortunately it also
prevents those that want to from hot-rodding their chips.
The AMD and Cyrix chips may not be marked on the bottom like Intel’s chips are, and of special
note is that the ink used on the AMD chips is very easy to wipe off. Since most AMD chips seem
to be capable of running well over their rated speed, this has contributed to a great deal of
remarking of those chips. If you purchase an AMD K6 processor or a system with that processor,
verify that the markings are the original AMD markings and that the speed rating on the chip is
what you really paid for.
The bottom line: If the price is too good to be true, ask before you buy. Are the parts really manufacturer-rated for the system speed?
To determine the rated speed of a CPU chip, look at the writing on the chip. Most of the time,
the part number will end in a suffix of –xxx where the xxx is a number indicating the maximum
speed. For example, –333 indicates that the chip is rated for 333MHz operation.
Caution
Be careful when running software to detect processor speed. Such programs can only tell you what speed the chip
is currently running at, not what the true rating is. Also ignore the speed indicator lights on the front of some cases.
These digital displays can literally be set via jumpers to read any speed you desire! They have no true relation to
actual system speed.
Most of the better diagnostics on the market such as the Norton Utilities from Symantec will read the processor ID
and stepping information. You can consult the processor manufacturer or Chapter 3, “Microprocessor Types and
Specifications,” for tables listing the various processor steppings to see exactly how yours stacks up.
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345 345
BIOS
SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE
BIOS Basics
BIOS Hardware/Software
Upgrading the BIOS
CMOS Setting Specifications
Year 2000 BIOS Issues
Plug-and-Play BIOS
BIOS Error Messages
CHAPTER 5
Motherboard BIOS
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BIOS Basics
It is often difficult for people to understand the difference between hardware and software in a
PC system. The differences can be difficult because they are both very much intertwined in the
system design, construction, and operation. Understanding these differences is essential to understanding the role of the BIOS in the system.
BIOS is a term that stands for basic input/output system. BIOS is really the link between hardware
and software in a system. Most people know the term BIOS by another name—device drivers, or
just drivers.
The BIOS is a single term that describes all the drivers in a system working together to act as an
interface between the hardware and the operating system software. What can be confusing is that
some of the BIOS is burned or flashed into a ROM chip that is both nonvolatile (it doesn’t get
erased when the power is turned off) and read-only. This is a core part of the BIOS, but not all of
it. The BIOS also includes ROM chips installed on adapter cards, as well as all the additional drivers loaded when your system boots up.
The combination of the motherboard BIOS, the adapter card BIOS, and the device drivers loaded
from disk contribute to the BIOS as a whole. The portion of the BIOS that is contained in ROM
chips both on the motherboard and in some adapter cards is sometimes called firmware, which is
a name given to software stored in chips rather than on disk. This causes some people to incorrectly think of the BIOS as a hardware component.
A PC system can be described as a series of layers—some hardware and some software—that interface with each other. In the most basic sense, you can break a PC down into four primary layers,
each of which can be broken down further into subsets. Figure 5.1 shows the four layers in a typical PC.
System “A”
Hardware
System “B”
Hardware
Non-Standard
Interface
System “A” ROM BIOS
& Device Drivers
System “B” ROM BIOS
& Device Drivers
Standard
Interface
Operating
System
Application Program
Figure 5.1
Operating
System
Standard
Interface
(API)
Application Program
PC system layers.
The purpose of the layered design is to allow for a given operating system and applications to run
on different hardware. Figure 5.1 shows how two different machines with different hardware can
each use a custom BIOS to interface the unique hardware to a common operating system and
applications. Thus, two machines with different processors, storage media, video display units,
and so on can run the same software.
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In this layered architecture, the application programs talk to the operating system via what is
called an API (Application Program Interface). The API varies according to the operating system
you are using and consists of the different commands and functions that the operating system
can perform for an application. For example, an application can call on the operating system to
load or save a file. This prevents the application itself from having to know how to read the disk,
send data to a printer, or perform any other of the many functions the operating system can provide. Because the application is completely insulated from the hardware, I can essentially run the
same applications on different systems; the application is designed to talk to the operating system rather than the hardware.
The operating system then interfaces or talks to the BIOS layer. The BIOS consists of all the individual driver programs that operate between the operating system and the actual hardware. As
such, the operating system never talks to the hardware directly; instead, it must always go
through the appropriate driver. This allows for a consistent way to talk to the hardware. It is normally the responsibility of the hardware manufacturer to provide drivers for its hardware. Because
the drivers must act between both the hardware and the operating system, the drivers are normally operating-system specific. Thus, the hardware manufacturer must offer different drivers so
that its hardware will work under DOS, Windows 9x, Windows NT, Windows 2000, OS/2, Linux,
and so on.
Because the BIOS layer looks the same to the operating system no matter what hardware is above
it (or underneath, depending on your point of view), we can have the same operating system
running on a variety of PCs. For example, you can run Windows 98 on two systems with different processors, hard disks, video adapters, and so on, yet Windows 98 will look and feel pretty
much the same on both of them. This is because the drivers provide the same basic functions no
matter which specific hardware is used.
As you can see from Figure 5.1, the application and operating systems layers can be identical
from system to system, but the hardware can differ radically. Because the BIOS consists of software drivers that act to interface the hardware to the software, the BIOS layer adapts to the
unique hardware on one end, but looks consistently the same to the operating system at the
other end.
The hardware layer is where most differences lie between different systems. It is up to the BIOS to
mask the differences between unique hardware so that the given operating system (and subsequently the application) can be run. In this chapter, we are focusing on the BIOS layer of the PC.
BIOS Hardware/Software
The BIOS itself is software that consists of all the various drivers that interface the hardware to
the operating system. The BIOS is unique compared to normal software in that it doesn’t all load
from disk; some of it is preloaded into chips installed in the system or on adapter cards.
The BIOS in a PC comes from three possible sources:
■ Motherboard ROM BIOS
■ Adapter Card BIOS (such as that found on a video card)
■ Loaded from disk (drivers)
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The motherboard BIOS is most often associated with hardware rather than software. This is
because the BIOS on the motherboard is contained in a ROM (read-only memory) chip on the
board, which contains the initial software drivers needed to get the system running. Years ago,
when running only DOS on basic PCs, this was enough so that no other drivers were needed; the
motherboard BIOS had everything that was necessary. The motherboard BIOS normally includes
drivers for all the basic system components, including the keyboard, the floppy drive, the hard
drive, the serial and parallel ports, and more. As systems became more complex, new hardware
was added for which no motherboard BIOS drivers existed. These included devices such as newer
video adapters, CD-ROM drives, SCSI hard disks, and so on.
Rather than requiring a new motherboard BIOS that would specifically support the new devices,
it was far simpler and more practical to copy any new drivers that were needed onto the system
hard disk and configure the operating system to load them at boot time. This is how most CDROM drives, sound cards, scanners, printers, PC-card (PCMCIA) devices, and so on are supported.
Because these devices don’t need to be active during boot time, the system can boot up from the
hard disk and wait to load the drivers during the initial operating system load.
Some drivers, however, must be active during boot time. For example, how will you be able to see
anything on the screen if your video card doesn’t have a set of drivers in a ROM somewhere,
rather than waiting to load them from the hard disk? The solution to this could be to provide a
motherboard ROM with the appropriate video drivers built in; however, this is impractical
because of the variety of cards, each needing its own drivers. You would end up with hundreds of
different motherboard ROMs, depending on which video card you had. Instead, when IBM was
designing the original PC, it created a better solution. It designed the PC’s motherboard ROM to
scan the slots looking for adapter cards with ROMs on them. If a card was found with a ROM on
it, the ROM was executed during the initial system startup phase, well before the system began
loading the operating system from the hard disk.
By putting the ROM-based drivers right on the card, you didn’t have to change your motherboard ROM to have built-in support for new devices, especially those that needed to be active
during boot time. A few different cards (adapter boards) will almost always have a ROM onboard,
including the following:
■ Video cards. All will have an onboard BIOS.
■ SCSI adapters. Those that support booting from SCSI hard drives have an onboard BIOS.
Note that, in most cases, the SCSI BIOS does not support any SCSI devices other than a
hard disk; if you use a SCSI CD-ROM, scanner, zip drive, and so on, you still need to load
the appropriate drivers for those devices from your hard disk.
■ Network cards. Those that support booting directly from a file server will have what is usually called a boot ROM or IPL (Initial Program Load) ROM onboard. This allows for PCs to
be configured on a LAN as diskless workstations—also called Net PCs, NCs (Network
Computers), or even smart terminals.
■ IDE or floppy upgrade boards. Boards that allow you to attach more or different types of drives that what is normally supported by the motherboard alone. These cards require an
onboard BIOS to enable these drives to be bootable.
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■ Y2K boards. Boards that incorporate BIOS fixes to update the century byte in the CMOS
RAM. These boards have a small driver contained in a BIOS, which monitors the year byte
for a change from 99 to 00. When this is detected, the driver updates the century byte from
19 to 20, correcting a flaw in some older motherboard BIOSes.
BIOS and CMOS RAM
Some people confuse BIOS with the CMOS RAM in a system. This confusion is aided by the fact that the Setup
program in the BIOS is used to set and store the configuration settings in the CMOS RAM. They are, in fact, two
totally separate components.
The BIOS on the motherboard is stored in a fixed ROM chip. Also on the motherboard is a chip called the
RTC/NVRAM chip, which stands for Real-Time Clock/Non-Volatile Memory. This is actually a digital clock chip
with a few extra bytes of memory thrown in.
The first one ever used in a PC was the Motorola MC146818 chip, which had 64 bytes of storage, of which 10
bytes were dedicated to the clock function. Although it is called nonvolatile, it is actually volatile, meaning that
without power, the time/date settings and the data in the RAM portion will, in fact, be erased. It is called nonvolatile because it is designed using CMOS (complementary metal-oxide semiconductor) technology, which results
in a chip that runs on very little power, and that power is provided by a battery in the system, not by the AC wall
current. This is also why most people incorrectly call this chip the CMOS RAM chip; although not technically accurate, that is easier to say than the RTC/NVRAM chip. Most RTC/NVRAM chips run on as little as 1 micro-amp
(millionth of an amp), which means they use very little battery power to run. Most will last five years before the
lithium battery runs out and the information stored gets erased.
When you enter your BIOS Setup, configure your hard disk parameters or other BIOS Setup settings, and save
them, these settings are written to the storage area in the RTC/NVRAM (otherwise called CMOS RAM) chip. Every
time your system boots up, it reads the parameters stored in the CMOS RAM chip to determine how the system
should be configured. A relationship exists between the BIOS and CMOS RAM, but they are two distinctly different
parts of the system.
Motherboard BIOS
All motherboards must have a special chip containing software we call the BIOS or ROM BIOS.
This ROM chip contains the startup programs and drivers that are used to get the system running
and act as the interface to the basic hardware in the system. A POST (power on self test) in the
BIOS also tests the major components in the system when you turn it on, and normally a setup
program used to store system configuration data in the CMOS (complementary metal-oxide semiconductor) memory powered by a battery on the motherboard. This CMOS RAM is often called
NVRAM (Non-Volatile RAM) because it runs on about 1 millionth of an amp of electrical current
and can store data for years when powered by a tiny lithium battery.
◊◊ See “ROM Hardware,” p. 350.
The BIOS is a collection of programs embedded in one or more chips, depending on the design of
your computer. That collection of programs is the first thing loaded when you start your computer, even before the operating system. Simply put, the BIOS in most PCs has four main functions:
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■ POST (power on self test). The POST tests your computer’s processor, memory, chipset, video
adapter, disk controllers, disk drives, keyboard, and other crucial components.
■ BIOS Setup. System configuration and setup program. This is usually a menu-driven program activated by pressing a special key during the POST, which allows you to configure
the motherboard and chipset settings along with the date and time, passwords, disk drives,
and other basic system settings. You also can control the power-management settings and
boot-drive sequence from the BIOS Setup. Some older 286 and 386 systems did not have
the Setup program in ROM and required that you boot from a special setup disk.
■ Bootstrap loader. A routine that reads the disk drives looking for a valid master boot sector. If
one meeting certain minimum criteria (ending in the signature bytes 55AAh) is found, then
the code within is executed. This master boot sector program then continues the boot
process by loading an operating system boot sector, which then loads the operating system
core files.
■ BIOS (basic input/output system). This refers to the collection of actual drivers used to act as a
basic interface between the operating system and your hardware when the system is booted
and running. When running DOS or Windows in safe mode, you are running almost solely
on ROM-based BIOS drivers because none are loaded from disk.
ROM Hardware
Read-only memory, or ROM, is a type of memory that can permanently or semi-permanently
hold data. It is called read-only because it is either impossible or difficult to write to. ROM is also
often called nonvolatile memory because any data stored in ROM will remain even if the power
is turned off. As such, ROM is an ideal place to put the PC’s startup instructions—that is, the software that boots the system—the BIOS.
Note that ROM and RAM are not opposites, as some people seem to believe. In fact, ROM is technically a subset of the system’s RAM. In other words, a portion of the system’s random access
memory address space is mapped into one or more ROM chips. This is necessary to contain the
software that enables the PC to boot up; otherwise, the processor would have no program in
memory to execute when it is powered on.
For example, when a PC is turned on, the processor automatically jumps to address FFFF0h,
expecting to find instructions to tell the processor what to do. This location is exactly 16 bytes
from the end of the first megabyte of RAM space, as well as the end of the ROM itself. If this
location were mapped into regular RAM chips, any data stored there would have disappeared
when the power was previously turned off, and the processor would subsequently find no
instructions to run the next time power was turned on. By placing a ROM chip at this address, a
system startup program can be permanently loaded into the ROM and will be available every
time the system is turned on.
◊◊ See “The Boot Process,” p. 1353.
◊◊ For more information about Dynamic RAM, see “DRAM,” p. 418.
Normally the system ROM will start at address F0000h, which is 64KB prior to the end of the first
megabyte. Because the ROM chip is normally 64KB in size, the ROM programs occupy the entire
last 64KB of the first megabyte, including the critical FFFF0h startup instruction address.
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Some think it is strange that the PC would start executing instructions 16 bytes from the end of
the ROM, but this design was intentional. All the ROM programmer has to do is to place a JMP
(jump) instruction at that address that instructs the processor to jump to the actual beginning of
the ROM—in most cases close to F0000h—which is about 64KB earlier in the memory map. It’s
like deciding to read every book starting 16 pages from the end, and then having all book publishers agree to place an instruction there to jump back the necessary number of pages to get to
page 1. By setting the startup location in this way, Intel allowed the ROM to grow to be any size,
all the while keeping it at the upper end of addresses in the first megabyte of the memory address
space.
The main ROM BIOS is contained in a ROM chip on the motherboard, but adapter cards with
ROMs are also on them as well. ROMs on adapter cards contain auxiliary BIOS routines and drivers needed by the particular card, especially for those cards that must be active early in the boot
process, such as video cards, for example. Cards that don’t need drivers active during boot (such
as sound cards) will not normally have a ROM because those drivers can be loaded from the hard
disk later in the boot process.
Because the BIOS is the main portion of the code stored in ROM, we often call the ROM the ROM
BIOS. In older PCs, the motherboard ROM BIOS could consist of up to five or six total chips, but
most PCs have only required a single chip for many years now.
Adapter cards that require drivers during the boot process need to have ROM onboard. This
includes cards such as video cards, most SCSI (small computer systems interface) cards (if you
want to boot from a SCSI hard drive), enhanced IDE controller cards, and some network cards
(for booting from the server). The ROM chip on these cards contains drivers and startup programs that will be executed by the motherboard ROM at boot time. This, for example, is how a
video card can be recognized and initialized, even though your motherboard ROM does not contain specific drivers for it. You wouldn’t want to load the initial VGA mode drivers from disk
because the screen would remain dark until those drivers were loaded.
Adapter card ROMs are automatically scanned and read by the motherboard ROM during the
early part of the boot process, during the POST (power on self test). The motherboard ROM scans
a special area of RAM reserved for adapter ROMs (addresses C0000-DFFFFh) looking for a 55AAh
signature byte pair that indicates the start of a ROM.
All adapter ROMs must start with 55AAh or they won’t be recognized by the motherboard. The
third byte indicates the size of the ROM in 512-byte units called paragraphs, and the fourth byte
is the actual start of the driver programs. The size byte is used by the motherboard ROM for testing purposes. The motherboard ROM adds all the bytes in the ROM and divides the sum by the
number of bytes. The result should produce a remainder of 100h. Thus, when creating a ROM for
an adapter, the programmer uses a “fill” byte at the end to get the checksum to come out right.
Using this checksum the motherboard tests each adapter ROM during the POST and flags any
that appear to have been corrupted.
The motherboard BIOS automatically runs the programs in any adapter ROMs it finds during the
scan. You see this in most systems when you turn your system on, and during the POST, you see
the video card BIOS initialize and announce its presence.
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ROM Shadowing
ROM chips by their nature are very slow, with access times of 150ns (nanoseconds, or billionths
of a second), compared to DRAM access times of 60ns or less. Because of this, in many systems
the ROMs are shadowed, which means they are copied into DRAM chips at startup to allow faster
access during normal operation. The shadowing procedure copies the ROM into RAM and then
assigns that RAM the same address as the ROM originally used, disabling the actual ROM in the
process. This makes the system seem as though it has 60ns (or whatever the RAM speed is) ROM.
The performance gain from shadowing is often very slight, and it can cause problems if not set
up properly, so in most cases, it is wise to shadow only the motherboard and maybe the video
card BIOS, and leave the others alone.
Mostly, shadowing is useful only if you are running 16-bit operating systems such as DOS or
Windows 3.x. If you are running a 32-bit operating system such as Windows 95, Windows 98,
Windows 2000, or Windows NT, shadowing is virtually useless because those operating systems
do not use the 16-bit ROM code while running. Instead, those operating systems load 32-bit drivers into RAM, which replace the 16-bit BIOS code used only during system startup.
Shadowing controls are found in the CMOS Setup program in the motherboard ROM, which is
covered in more detail later in this chapter.
There are four types of ROM chips:
■ ROM. Read-only memory
■ PROM. Programmable ROM
■ EPROM. Erasable PROM
■ EEPROM. Electrically-erasable PROM, also called a flash ROM
No matter which type of ROM your system uses, the data stored in a ROM chip is nonvolatile
and will remain indefinitely unless intentionally erased or overwritten (in those where that is
possible).
Table 5.1 lists the identifying part numbers typically used for each type of ROM chip, along with
any other identifying information.
Table 5.1
ROM Chip Part Numbers
ROM Type
Part Number
ROM
No longer in use
PROM
27nnnn
EPROM
27nnnn
EEPROM
28xxxx or
29xxxx
Other
Quartz Window
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Mask ROM
Originally, most ROMs were manufactured with the binary data (0s and 1s) already “cast in” or
integrated into the die. The die represents the actual silicon chip itself. These are called Mask
ROMs because the data is formed into the mask from which the ROM die is photolithographically produced. This type of manufacturing method is economical if you are making hundreds of
thousands of ROMs with the same information. If you have to change a single bit, however, you
must remake the mask, which is an expensive proposition. Because of costs and inflexibility,
nobody uses Mask ROMs anymore.
Mask ROMs are exactly analogous to prerecorded CD-ROMs. Some people think a CD-ROM is
first manufactured as a blank and then the data is written to it by laser, but that is not true. A
CD-ROM is literally a piece of plastic that is stamped in a press, and the data is directly molded
in, not written. The only actual recording was done with the master disc from which the molds
or stamps are made.
PROM
PROMs are a type of ROM that is blank when new and that must be programmed with whatever
data you want. The PROM was invented in the late 1970s by Texas Instruments and has been
available in sizes from 1KB (8Kb) to 2MB (16Mb) or more. They can be identified by their part
numbers, which are usually 27nnnn—where the 27 indicates the TI type PROM, and the nnnn
indicates the size of the chip in kilobits (not bytes). For example, most PCs that used PROMs
came with 27512 or 271000 chips, which indicate 512Kb (64KB) or 1Mb (128KB).
Note
Since 1981, all cars sold in the US have used onboard computers with some form of ROM containing the control
software. My ‘89 Pontiac Turbo Trans Am came with an onboard computer containing a 2732 PROM, which was
a 32Kb (4KB) chip in the ECM (Electronic Control Module or vehicle computer) under the dash. This chip contained a portion of the vehicle operating software as well as all the data tables describing spark advance, fuel
delivery, and other engine and vehicle operating parameters. Many devices with integrated computers use PROMs
to store their operating programs.
Although we say these chips are blank when new, they are technically preloaded with binary 1s.
In other words, a 1Mb ROM chip used in a modern PC would come with 1 million (actually
1,048,576) bit locations, each containing a binary 1. A blank PROM can then be programmed,
which is the act of writing to it. This normally requires a special machine called a device programmer, a ROM programmer, or a ROM burner (see Figure 5.2).
We sometimes refer to programming the ROM as “burning” it, because that is technically an apt
description of the process. Each binary 1 bit can be thought of as a fuse, which is intact. Most
chips run on 5 volts, but when we program a PROM, we place a higher voltage (normally 12
volts) at the various addresses within the chip. This higher voltage actually blows or burns the
fuses at the locations we desire, thus turning any given 1 into a 0. Although we can turn a 1 into
a 0, you should note that the process is irreversible; that is, we cannot turn a 0 back into a 1.
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KE/EPROM/P
AL/GANG/SE
T
PROGRAMM
ER
SKT 1
Figure 5.2
SKT 2
SKT 3
SKT 4
Typical gang (multisocket) device programmer (PROM burner).
The device programmer examines the program you want to write into the chip and then selectively changes only the 1s to 0s where necessary in the chip.
PROM chips are often referred to as OTP (one time programmable) chips for this reason. They
can be programmed once and never erased. Most PROMs are very inexpensive, about $3 for a
typical PC motherboard PROM, so if you want to change the program in a PROM, you discard it
and program a fresh one with the new data.
The act of programming a PROM takes anywhere from a few seconds to a few minutes, depending on the size of the chip and the algorithm used by the programming device. Figure 5.2 shows
an illustration of a typical PROM programmer that has multiple sockets. This is called a gang programmer and can program several chips at once, saving time if you have several chips to write
with the same data. Less expensive programmers are available with only one socket, which is fine
for most individual use.
I use and recommend a very inexpensive programmer from a company called Andromeda
Research (see Vendor List on the CD). Besides being economical, their unit has the advantage of
connecting to a PC via the parallel port for fast and easy data transfer of files between the PC and
the programming unit. Their unit is also portable and comes built into a convenient carrying
case. It is operated by an included menu-driven program you install on the connected PC. The
program contains several features, including a function that allows you to read the data from a
chip and save it in a file on your system, as well as to write a chip from a data file, verify that a
chip matches a file, and verify that a chip is blank before programming begins.
Chapter 4, “Motherboards and Buses,” shows how I used my PROM programmer to modify the
BIOS in some of my older PCs. With today’s systems primarily using flash ROMs, this capability is
somewhat limited, but I include the information because I think it is very interesting.
Note
I even used my PROM programmer to reprogram the PROM in my 1989 Turbo Trans Am, changing the factory
preset speed and rpm limiters, turbocharger boost, torque converter lockup points, spark advance, fuel delivery,
idle speed, and much more! I also incorporated a switch box under the dash that allows me to switch among four
different chips, even while the vehicle is running. One chip I created I call the “valet chip,” which, when engaged,
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cuts off the fuel injectors at a preset speed of 36 miles per hour and restarts them when the vehicle coasts down to
35mph. I imagine this type of modification would be useful for those with teenagers driving, because you could set
the mph or engine rpm limit to whatever you want! Another chip I created cuts off fuel to the engine altogether,
which I engage for security purposes when the vehicle is parked. No matter how clever, a thief will not be able to
steal this car unless he tows it away. If you are interested in such a chip-switching device or custom chips for your
Turbo Trans Am or Buick Grand National, contact Casper’s Electronics (see the Vendor List on the CD-ROM accompanying this book). For other vehicles with replaceable PROMs, companies such as Superchips, Hypertech, or
Evergreen offer custom PROMs for improved performance (see the Vendor List on the CD). I installed a Superchips
chip in a Ford Explorer I had, and it made a dramatic improvement in engine operation and vehicle performance.
EPROM
One variation of the PROM that has been very popular is the EPROM. An EPROM is a PROM that
is erasable. An EPROM chip can be easily recognized by the clear quartz crystal window set in the
chip package directly over the die (see Figure 5.3). You can actually see the die through the window! EPROMs have the same 27xxxx part-numbering scheme as the standard PROM, and they
are functionally and physically identical except for the clear quartz window above the die.
Figure 5.3
An EPROM showing the quartz window for ultraviolet erasing.
The purpose of the window is to allow ultraviolet light to reach the chip die because the EPROM
is erased by exposure to intense UV light. The window is quartz crystal because regular glass
blocks UV light. You can’t get a suntan through a glass window!
Note
The quartz window makes the EPROMS more expensive than the OTP (One Time Programmability) PROMs. This
extra expense is needless if erasability is not important.
The UV light erases the chip by causing a chemical reaction, which essentially melts the fuses
back together! Thus, any binary 0s in the chip become 1s, and the chip is restored to new condition with binary 1s in all locations. To work, the UV exposure must be at a specific wavelength
(2,537 angstroms), at a fairly high intensity (12,000 uw/cm2), in close proximity (2–3cm, or about
1 inch), and last for between 5 and 15 minutes duration. An EPROM eraser (see Figure 5.4) is a
device that contains a UV light source (usually a sunlamp-type bulb) above a sealed compartment
drawer where you place the chip or chips.
Figure 5.4 shows a professional type EPROM eraser that can handle up to 50 chips at a time. I use
a much smaller and less expensive one called the DataRase by Walling Co. (see the Vendor List
on the CD). This device erases up to four chips at a time and is both economical and portable.
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A professional EPROM eraser.
The quartz crystal window on an EPROM is normally covered by tape, which prevents accidental
exposure to UV light. UV light is present in sunlight, of course, and even in standard room lighting, so that over time a chip exposed to the light may begin to degrade. For this reason after a
chip is programmed, it is a good idea to put a sticker over the window to protect it.
EEPROM/Flash ROM
A newer type of ROM is the EEPROM, which stands for Electrically Erasable PROM. These chips
are also called flash ROMs and are characterized by their capability to be erased and reprogrammed directly in the circuit board they are installed in, with no special equipment required.
By using an EEPROM, or flash ROM, it is possible to erase and reprogram the motherboard ROM
in a PC without removing the chip from the system or even opening up the system chassis!
With a flash ROM or EEPROM, you don’t need a UV eraser or device programmer to program or
erase chips. Not only do virtually all PC motherboards built since 1994 use flash ROMs or
EEPROMs, most automobiles built since then also use them as well. For example my `94 Chevy
Impala SS has a PCM (Powertrain Control Module) with an integral flash ROM.
The EEPROM or flash ROM can be identified by a 28xxxx or 29xxxx part number, as well as by
the absence of a window on the chip. Having an EEPROM or flash ROM in your PC motherboard
means you can now easily upgrade the motherboard ROM without having to swap chips. In most
cases, you will download the updated ROM from the motherboard manufacturer’s Web site and
then run a special program they provide to update the ROM. This procedure is described in more
detail later in this chapter.
I recommend that you periodically check with your motherboard manufacturer to see whether an
updated BIOS is available for your system. An updated BIOS may contain bug fixes or enable new
features not originally found in your system. You might find fixes for a potential year 2000 date
problem, for example, or new drivers to support booting from LS-120 (120MB floppy) drives.
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Note
For the auto enthusiasts out there, you might want to do the same for your car; that is, check to see whether ROM
upgrades are available for your vehicle’s computer. Now that updates are so easy and inexpensive, vehicle manufacturers are releasing bug-fix ROM upgrades that correct operational problems or improve vehicle performance. In
most cases, you will have to check with your dealer to see whether any new vehicle ROMs are available. If you
have a GM car, GM has a site on the Web where you can get information about the BIOS revisions available for
your car, which it calls Vehicle Calibrations. The GM Vehicle Calibration Information site address is
http://207.74.147.14/vci/
When you enter your VIN (vehicle identification number), this page displays the calibration history for the vehicle,
which is a list of all the different flash ROM upgrades (calibrations) developed since the vehicle was new. For
example, when I entered the VIN on my 1994 Impala, I found that five flash ROM calibrations had been released
over the years, and my car had only the second revision installed originally, meaning there had been three newer
ROMs than the one I had! The fixes in the various calibration updates are also listed. A trip to the dealer with this
information enabled them to use their diagnostic computer to connect to my car and reflash the PCM with the latest
software, which, in my case, fixed several problems including engine surging under specific conditions, shift clunks,
erroneous “check engine” light warnings, and several other minor problems.
With the flash ROM capability, I began experimenting with running calibrations originally intended for other vehicles, and I now run a modified Camaro calibration loaded into the flash ROM in my Impala. The spark-advance
curve and fuel delivery parameters are much more aggressive in the Camaro calibration, as are the transmission
shift points and other features. If you are interested in having a custom program installed in your flash ROM
equipped vehicle, I recommend you contact Wright Automotive or Evergreen Performance (see the Vendor List on
the CD).
These days, many objects with embedded computers controlling them are using flash ROMs.
Pretty soon you’ll be taking your toaster in for flash ROM upgrades as well! The method for locating and updating your PC motherboard flash ROMs is shown in Chapter 4.
Other devices may have flash ROMs as well; for example, I have updated the flash ROMs in my
Motorola ISDN modem as well as in my Kodak digital camera. Both of these items had minor
quirks that were fixed by updating their internal ROM code, which was as easy as downloading a
file from their respective Web sites and running the update program included in the file.
Flash ROMs are also frequently used to add new capabilities to peripherals or to update peripherals, such as modems, to the latest standards; for example, updating a modem from X2 or Kflex to
v.90.
ROM BIOS Manufacturers
A number of popular BIOS manufacturers in the market today supply the majority of motherboard and system manufacturers with the code for their ROMs. This section discusses the various
versions available.
Several companies have specialized in the development of a compatible ROM BIOS product. The
three major companies that come to mind in discussing ROM BIOS software are American
Megatrends, Inc. (AMI), Award Software, and Phoenix Software. Each company licenses its ROM
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BIOS to motherboard manufacturers so those manufacturers can worry about the hardware rather
than the software. To obtain one of these ROMs for a motherboard, the OEM (Original
Equipment Manufacturer) must answer many questions about the design of the system so that
the proper BIOS can be either developed or selected from those already designed. Combining a
ROM BIOS and a motherboard is not a haphazard task. No single, generic, compatible ROM
exists, either. AMI, Award, Microid Research, and Phoenix ship many variations of their BIOS
code to different board manufacturers, each one custom- tailored to that specific motherboard.
Recently, some big changes have occurred in the BIOS industry. Phoenix landed a contract with
Intel and now provides all of Intel’s motherboard BIOSes, replacing AMI, who previously had the
contract. This is a big deal because Intel sells about 80 percent or more of all PC motherboards.
What that basically means is that if you purchase a PC today, you will probably be getting an
Intel-made motherboard with the new Phoenix BIOS.
Another development is that in late 1998, Phoenix bought Award, and all its new products will
be under the Phoenix name. Thus, the big-three BIOS developers are now reduced to the big
two—Phoenix and AMI. Many of the offshore motherboard manufacturers still continue to use
the AMI or Award BIOS. However, Phoenix is currently the leading BIOS company. It is not only
developing the BIOS for most newer systems on the market, but it also is the primary BIOS developer responsible for new BIOS development and new BIOS standards.
OEMs
Many OEMs (original equipment manufacturers) have developed their own compatible ROMs
independently. Companies such as Compaq and AT&T have developed their own BIOS products
that are comparable to those offered by AMI, Phoenix, Award, and others. These companies also
offer upgrades to newer versions that often can offer more features and improvements or fix
problems with the older versions. If you use a system with a proprietary ROM, make sure that it
is from a larger company with a track record and one that will provide updates and fixes as necessary. Ideally, upgrades should be available for download from the Internet.
Most OEMs have their BIOS written for them by a third-party company. For example, Hewlett
Packard contracts with Phoenix, a well-known BIOS supplier, to develop the motherboard BIOSes
used in all the HP Vectra PCs. Note that even though Phoenix may have done the development,
you still have to get any upgrades or fixes from Hewlett Packard. This is really true for all systems
because all motherboard manufacturers customize the BIOS for their boards.
Intel, today the largest manufacturer of motherboards in the world, used to use AMI for its BIOS,
but during 1997, it switched over to Phoenix for all its newer systems. Today Intel supplies versions of the Phoenix BIOS with all its boards. Phoenix is again the largest BIOS supplier in the
world; it is found in the majority of motherboards today.
AMI
Although AMI customizes the ROM code for a particular system, it does not sell the ROM source
code to the OEM. An OEM must obtain each new release as it becomes available. Because many
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OEMs don’t need or want every new version developed, they might skip several version changes
before licensing a new one. The AMI BIOS is currently the most popular BIOS in PC systems.
Newer versions of the AMI BIOS are called Hi-Flex because of the high flexibility found in the
BIOS configuration program. The AMI Hi-Flex BIOS is used in Intel, AMI, and many other manufacturers’ motherboards. One special AMI feature is that it is the only third-party BIOS manufacturer to make its own motherboard.
During powerup, the BIOS ID string is displayed on the lower-left part of the screen. This string
tells you valuable information about which BIOS version you have and about certain settings that
are determined by the built-in setup program.
Tip
A good trick to help you view the BIOS ID string is to shut down and either unplug your keyboard or hold down a
key as you power back on. This causes a keyboard error, and the string will remained displayed.
The primary BIOS Identification string (ID String 1) is displayed by any AMI BIOS during the
POST (power on self test) at the bottom-left corner of the screen, below the copyright message.
Two additional BIOS ID strings (ID Strings 2 and 3) can be displayed by the AMI Hi-Flex BIOS by
pressing the Insert key during POST. These additional ID strings display the options that are
installed in the BIOS.
The general BIOS ID String 1 format for older AMI BIOS versions is shown in Table 5.2.
Table 5.2
ABBB-NNNN-mmddyy-KK
Position
Description
A
BIOS Options:
D = Diagnostics built in
S = Setup built in
E = Extended Setup built in
BBB
Chipset or Motherboard Identifier:
C&T = Chips & Technologies chipset
NET = C&T NEAT 286 chipset
286 = Standard 286 motherboard
SUN = Suntac chipset
PAQ = Compaq motherboard
INT = Intel motherboard
AMI = AMI motherboard
G23 = G2 chipset 386 motherboard
NNNN
The manufacturer license code reference number
mmddyy
The BIOS release date, mm/dd/yy
KK
The AMI keyboard BIOS version number.
The BIOS ID String 1format for AMI Hi-Flex BIOS versions is shown in Table 5.3.
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AB-CCcc-DDDDDD-EFGHIJKL-mmddyy-MMMMMMMM-N
Position
Description
A
Processor Type:
0 = 8086 or 8088
2 = 286
3 = 386
4 = 486
5 = Pentium
6 = Pentium Pro/II
Size of BIOS:
0 = 64KB BIOS
1 = 128KB BIOS
Major and minor BIOS version number
Manufacturer license code reference number
0036xx = AMI 386 motherboard, xx = Series #
0046xx = AMI 486 motherboard, xx = Series #
0056xx = AMI Pentium motherboard, xx = Series #
0066xx = AMI Pentium Pro motherboard, xx = Series #
1 = Halt on POST Error
1 = Initialize CMOS every boot
1 = Block pins 22 and 23 of the keyboard controller
1 = Mouse support in BIOS/keyboard controller
1 = Wait for <F1> key on POST errors
1 = Display floppy error during POST
1 = Display video error during POST
1 = Display keyboard error during POST
BIOS Date, mm/dd/yy
Chipset identifier or BIOS name
Keyboard controller version number
B
CCcc
DDDDDD
E
F
G
H
I
J
K
L
mmddyy
MMMMMMMM
N
AMI Hi-Flex BIOS ID String 2 is shown in Table 5.4.
Table 5.4
AAB-C-DDDD-EE-FF-GGGG-HH-II-JJJ
Position
Description
AA
B
Keyboard controller pin number for clock switching.
Keyboard controller clock switching pin function:
H = High signal switches clock to high speed.
L = High signal switches clock to low speed.
C = Clock switching through chipset registers:
0 = Disable.
1 = Enable.
Port address to switch clock high.
Data value to switch clock high.
Mask value to switch clock high.
Port address to switch clock low.
Data value to switch clock low.
Mask value to switch clock low.
Pin number for Turbo Switch Input.
DDDD
EE
FF
GGGG
HH
II
JJJ
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AMI Hi-Flex BIOS ID String 3 is shown in Table 5.5.
Table 5.5
AAB-C-DDD-EE-FF-GGGG-HH-II-JJ-K-L
Position
Description
AA
Keyboard controller pin number for cache control.
B
Keyboard controller cache control pin function:
H = High signal enables the cache.
L = High signal disables the cache.
C
DDD
1 = High signal is used on the keyboard controller pin.
Cache control through chipset registers:
0 = Cache control off.
1 = Cache control on.
EE
Port address to enable cache.
FF
Data value to enable cache.
GGGG
Mask value to enable cache.
HH
Port address to disable cache.
II
Data value to disable cache.
JJ
Mask value to disable cache.
K
Pin number for resetting the 82335 memory controller.
L
BIOS Modification Flag:
0 = The BIOS has not been modified.
1–9, A–Z = Number of times the BIOS has been modified.
The AMI BIOS has many features, including a built-in setup program activated by pressing the
Delete or Esc key in the first few seconds of booting up your computer. The BIOS prompts you
briefly as to which key to press and when to press it. The AMI BIOS offers user-definable hard
disk types, essential for optimal use of many IDE or ESDI drives. The 1995 and newer BIOS versions also support enhanced IDE drives and will autoconfigure the drive parameters.
A unique feature of some of the AMI BIOS versions was that in addition to the setup, they had a
built-in, menu-driven diagnostics package, essentially a very limited version of the standalone
AMIDIAG product. The internal diagnostics are not a replacement for more comprehensive diskbased programs, but they can help in a pinch. The menu-driven diagnostics do not do extensive
memory testing, for example, and the hard disk low-level formatter works only at the BIOS level
rather than at the controller register level. These limitations often have prevented it from being
capable of formatting severely damaged disks. Most newer AMI BIOS versions no longer include
the full diagnostics.
AMI doesn’t produce BIOS documentation; it leaves that up to the motherboard manufacturers
who include their BIOS on the motherboard. However, AMI has published a detailed version of
its documentation called the Programmer’s Guide to the AMIBIOS, published by
Windcrest/McGraw-Hill and available under the ISBN 0-07-001561-9. This is a book written by
AMI engineers that describes all the BIOS functions, features, error codes, and more. I recommend
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this book for users with an AMI BIOS in their system because this provides a complete version of
the documentation for which they may have been looking.
The AMI BIOS is sold through distributors, a list of which is available at its Web site. However,
keep in mind that you cannot buy upgrades and replacements directly from AMI, and AMI produces upgrades only for its own motherboards. If you have a non-AMI motherboard with a customized AMI BIOS, you will have to contact the motherboard manufacturer for an upgrade.
Award
Award is unique among BIOS manufacturers because it sells its BIOS code to the OEM and allows
the OEM to customize the BIOS. Of course, then the BIOS no longer is Award BIOS, but rather a
highly customized version. AST uses this approach on its systems, as do other manufacturers, for
total control over the BIOS code without having to write it from scratch. Although AMI and
Phoenix customize the ROM code for a particular system, they do not sell the ROM’s source code
to the OEM. Some OEMs that seem to have developed their own ROM code started with a base of
source code licensed to them by Award or some other company.
The Award BIOS has all the normal features you expect, including a built-in setup program activated by pressing Ctrl+Alt+Esc or a particular key on startup (normally prompted on the screen).
This setup offers user-definable drive types, required to fully use IDE or ESDI hard disks. The
POST is good, and Award runs technical support on its Web site at http://www.award.com.
Award was purchased by Phoenix in late 1998, and in the future, its BIOS will be available under
the Phoenix name. However, it will continue to support its past BIOS versions and develop
updates if necessary.
Phoenix
The Phoenix BIOS for many years has been a standard of compatibility by which others are
judged. It was one of the first third-party companies to legally reverse-engineer the IBM BIOS
using a “clean room” approach. In this approach, a group of engineers studied the IBM BIOS and
wrote a specification for how that BIOS should work and what features should be incorporated.
This information then was passed to a second group of engineers who had never seen the IBM
BIOS. They could then legally write a new BIOS to the specifications set forth by the first group.
This work would then be unique and not a copy of IBM’s BIOS; however, it would function the
same way.
The Phoenix BIOS excels in two areas that put it high on my list of recommendations. One is
that the POST is excellent. The BIOS outputs an extensive set of beep codes that can be used to
diagnose severe motherboard problems that would prevent normal operation of the system. In
fact, with beep codes alone, this POST can isolate memory failures in Bank 0 right down to the
individual SIMM or DIMM module. The Phoenix BIOS also has an excellent setup program free
from unnecessary frills, but one that offers all the features the user would expect, such as userdefinable drive types, and so on. The built-in setup is activated by pressing Ctrl+Alt+S,
Ctrl+Alt+Esc, or a particular key on startup, such as F2 on most newer systems, depending on the
version of BIOS you have.
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The second area in which Phoenix excels is the documentation. Not only are the manuals that
you get with the system detailed, but Phoenix has also written a set of BIOS technical-reference
manuals that are a standard in the industry. The set consists of three books, titled System BIOS for
IBM PC/XT/AT Computers and Compatibles, CBIOS for IBM PS/2 Computers and Compatibles, and
ABIOS for IBM PS/2 Computers and Compatibles. In addition to being an excellent reference for the
Phoenix BIOS, these books serve as an outstanding overall reference to the BIOS in general.
Phoenix has extensive technical support and documentation on its Web site at
http://www.phoenix.com, as does its largest nationwide distributor, Micro Firmware, Inc. at
http://www.firmware.com, or check the phone numbers listed in the Vendor list on the CD.
Micro Firmware offers upgrades to some older systems with a Phoenix BIOS, including many
Packard Bell, Gateway 2000 (with Micronics motherboards), Micron Technologies, and other systems. For most systems, especially newer ones, you will need to get any BIOS updates from the
system or motherboard manufacturer.
These companies’ products are established as ROM BIOS standards in the industry, and frequent
updates and improvements ensure that a system containing these ROMs will have a long life of
upgrades and service.
Microid Research (MR) BIOS
Microid Research is an interesting BIOS supplier. It primarily markets upgrade BIOSes for older
Pentium and 486 motherboards that were abandoned by their original manufacturers. As such, it
is an excellent upgrade for adding new features and performance to an older system. Microid
Research BIOS upgrades are sold through Unicore Software.
Upgrading the BIOS
In this section, you learn that ROM BIOS upgrades can improve a system in many ways. You also
learn that the upgrades can be difficult and may require much more than plugging in a generic
set of ROM chips.
The ROM BIOS, or read-only memory basic input/output system, provides the crude brains that
get your computer’s components working together. A simple BIOS upgrade can often give your
computer better performance and more features.
The BIOS is the reason that different operating systems can operate on virtually any
PC-compatible system despite hardware differences. Because the BIOS communicates with the
hardware, the BIOS must be specific to the hardware and match it completely. Instead of creating
their own BIOSes, many computer makers buy a BIOS from specialists such as American
Megatrends, Inc. (AMI), Award Software (now part of Phoenix), Microid Research, or Phoenix
Technologies Ltd. A motherboard manufacturer that wants to license a BIOS must undergo a
lengthy process of working with the BIOS company to tailor the BIOS code to the hardware. This
process is what makes upgrading a BIOS somewhat problematic; the BIOS usually resides on ROM
chips on the motherboard and is specific to that motherboard model or revision. In other words,
you must get your BIOS upgrades from your motherboard manufacturer.
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Often, in older systems, you must upgrade the BIOS to take advantage of some other upgrade. To
install some of the larger and faster IDE (Integrated Drive Electronics) hard drives and LS-120
(120MB) floppy drives in older machines, for example, you may need a BIOS upgrade. Some
machines are still being sold with older BIOSes that do not support hard drives larger than 8GB,
for example.
The following list shows the primary functions of a ROM BIOS upgrade:
■ Adding LS-120 (120MB) floppy drive support (also known as a SuperDrive)
■ Adding support for hard drives greater than 8GB
■ Adding support for Ultra-DMA/33 IDE hard drives
■ Adding support for bootable ATAPI CD-ROM drives
■ Adding or improving Plug-and-Play support and compatibility
■ Correcting year-2000 and leap-year bugs
■ Correcting known bugs or compatibility problems with certain hardware and software
■ Adding support for newer types of processors
If you are installing newer hardware or software, and even though you follow all the instructions
properly, you can’t get it to work, specific problems may exist with the BIOS that an upgrade
might fix. This is especially true for newer operating systems. Many systems need to have a BIOS
update to properly work with the plug-and-play features of Windows 95 and 98, and the same is
true for Windows 2000. Because these things are random and vary from board to board, it pays to
periodically check the board manufacturer’s Web site to see if any updates are posted and what
problems they will fix.
Where to Get Your BIOS Update
For most BIOS upgrades, you must contact the motherboard manufacturer by phone or download
the upgrade from its Web site. The BIOS manufacturers do not offer BIOS upgrades because the
BIOS in your motherboard did not actually come from them. In other words, although you think
you have a Phoenix, AMI, or Award BIOS, you really don’t! Instead, you have a custom version of
one of these BIOSes, which was licensed by your motherboard manufacturer and uniquely customized for its board. As such, you must get any BIOS upgrades from the motherboard manufacturer because they must be customized for your board as well.
In the case of Phoenix or Award, another option may exist. A company called Unicore specializes
in providing Award BIOS upgrades. Unicore may be able to help you out if you can’t find your
motherboard manufacturer or if it is out of business. Phoenix has a similar deal with
MicroFirmware, a company it has licensed to provide various BIOS upgrades. If you have a
Phoenix or an Award BIOS and your motherboard manufacture can’t help you, contact one of
these companies for a possible solution. Microid Research (sold through Unicore) is another
source of BIOS upgrades for a variety of older and otherwise obsolete boards. They are available
for boards that originally came with AMI, Award, or Phoenix BIOSes, and they add new features
to older boards that have been abandoned by their original manufacturers. Contact them or
Unicore for more information.
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When seeking a BIOS upgrade for a particular motherboard (or system), you will need to know
the following information:
■ The make and model of the motherboard (or system)
■ The version of the existing BIOS
■ The type of CPU (for example, Pentium MMX, AMD K6, Cyrix/IBM 6x86MX, MII, Pentium
II, and so on)
You can usually identify the BIOS you have by watching the screen when the system is first powered up. It helps to turn the monitor on first because some take a few seconds to warm up, and
often the BIOS information is displayed for only a few seconds.
Tip
Look for any copyright notices or part number information. Sometimes you can press the Pause key on the keyboard to freeze the POST, allowing you to take your time to write down the information. Pressing any other key will
then cause the POST to resume.
You can also often find the BIOS ID information in the BIOS Setup screens.
After you have this information, you should be able to contact the motherboard manufacturer to
see whether a new BIOS is available for your system. If you go to the Web site, check to see
whether a version exists that is newer than the one you have. If so, you can download it and
install it in your system.
Determining Your BIOS Version
Most BIOSes display version information on the screen when the system is first powered up. In
some cases the monitor takes too long to warm up, and you may miss this information because it
is only displayed for a few seconds. Try turning your monitor on first, and then your system,
which will make it easier to see. You can usually press the Pause key on the keyboard when the
BIOS ID information is being displayed; this freezes it so you can record the information. Pressing
any other key will allow the system startup to resume.
Backing Up Your BIOS’s CMOS Settings
A motherboard BIOS upgrade will usually wipe out the BIOS Setup settings in the CMOS RAM.
Therefore, you should record these settings, especially the important ones such as hard disk parameters. Some software programs, such as the Norton Utilities, can save and restore CMOS settings, but unfortunately, these types of programs are often useless in a BIOS upgrade situation.
This is because sometimes the new BIOS will offer new settings or change the positions of the
stored data in the CMOS RAM, which means you don’t want to do an exact restore. Also with the
variety of different BIOSes out there, I have yet to find a CMOS RAM backup and restore program
that worked on more than just a few specific systems.
You are better off manually recording your BIOS Setup parameters, or possibly connecting a
printer to your system and using the Shift+Prtsc (Print Screen) function to print out each of the
setup screens. Some shareware programs could print or even save and restore the BIOS Setup
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settings stored in the CMOS RAM, but these were BIOS version specific and would not work on
any system. Most of these programs were useful during the 286-386 era, but the increasing variety of newer systems, especially those with Plug-and-Play capabilities, have rendered most of
these older programs useless.
Keyboard-Controller Chips
In addition to the main system ROM, older AT-class (286 and later) computers also have a keyboard controller or keyboard ROM, which is a keyboard-controller microprocessor with its own
built-in ROM. This is often found in the Super I/O or South Bridge chips on most newer boards.
The keyboard controller was originally an Intel 8042 microcontroller, which incorporates a
microprocessor, RAM, ROM, and I/O ports. This was a 40-pin chip that often had a copyright
notice identifying the BIOS code programmed into the chip. Modern motherboards have this
function integrated into the chipset, specifically the Super I/O or South Bridge chips, so you
won’t see the old 8042 chip anymore.
The keyboard controller controls the reset and A20 lines and also deciphers the keyboard scan
codes. The A20 line is used in extended memory and other protected-mode operations. In many
systems, one of the unused ports is used to select the CPU clock speed. Because of the tie-in with
the keyboard controller and protected-mode operation, many problems with keyboard controllers
became evident on these older systems when upgrading from DOS to Windows 95/98, NT, or
Windows 2000.
Problems with the keyboard controller were solved in most systems in the early 1990s, so you
shouldn’t have to deal with this issue in systems newer than that. With older systems, when you
upgraded the BIOS in the system, the BIOS vendor often included a new keyboard controller.
Using a Flash BIOS
Virtually all PCs built since 1996 include a flash ROM to store the BIOS. A flash ROM is a type of
EEPROM (Electrically Erasable Programmable Read-Only Memory) chip that you can erase and
reprogram directly in the system without special equipment. Older EPROMs required a special
ultraviolet light source and an EPROM programmer device to erase and reprogram them, whereas
flash ROMs can be erased and rewritten without even removing them from the system.
Using flash ROM enables a user to download ROM upgrades from a Web site or to receive them
on disk; you then can load the upgrade into the flash ROM chip on the motherboard without
removing and replacing the chip. Normally, these upgrades are downloaded from the manufacturer’s Web site, and then an included utility is used to create a bootable floppy with the new
BIOS image and the update program. It is important to run this procedure from a boot floppy so
that no other software or drivers are in the way that might interfere with the update. This
method saves time and money for both the system manufacturer and the end user.
Sometimes the flash ROM in a system is write-protected, and you must disable the protection
before performing an update, usually by means of a jumper or switch that controls the lock on
the ROM update. Without the lock, any program that knows the right instructions can rewrite
the ROM in your system—not a comforting thought. Without the write-protection, it is
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conceivable that virus programs could be written that copy themselves directly into the ROM
BIOS code in your system. Even without a physical write-protect lock, modern flash ROM BIOSes
have a security algorithm that helps to prevent unauthorized updates. This is the technique that
Intel uses on its motherboards.
Note that motherboard manufacturers will not notify you when they upgrade the BIOS for a particular board. You must periodically log in to their Web sites to check for updates. Normally, any
flash updates are free.
Before proceeding with a BIOS upgrade, you must first locate and download the updated BIOS
from your motherboard manufacturer. Consult the Vendor List on the CD to find the Web site
address or other contact information for your motherboard manufacturer. Log in to their Web
site and follow the menus to the BIOS updates page, and then select and download the new BIOS
for your motherboard.
The BIOS upgrade utility is contained in a self-extracting archive file that can initially be downloaded to your hard drive, but it must be extracted and copied to a floppy before the upgrade can
proceed. Different motherboard manufacturers have slightly different procedures and programs to
accomplish a flash ROM upgrade, so it is best if you read the directions usually included with the
update. I include instructions here for Intel motherboards because they are by far the most common.
The Intel BIOS upgrade utility will fit on a floppy disk and provides the capability to save, verify,
and update the system BIOS. The upgrade utility also provides the capability to install alternative
languages for BIOS messages and the SETUP utility.
The first step in the upgrade after downloading the new BIOS file is to enter the CMOS setup and
write down your existing CMOS settings because they will be erased during the upgrade. Then
you create a DOS boot floppy and uncompress or extract the BIOS upgrade files to the floppy
from the file you downloaded. Then you reboot on the newly created upgrade disk and follow
the menus for the actual reflash procedure.
Here is a step-by-step procedure for the process:
1. Save your CMOS RAM setup configuration. You can do so by pressing the appropriate key
during boot (F1 with an AMI BIOS, F2 with a Phoenix BIOS) and write down all your current CMOS settings. You may also be able to print the screens if you have a printer connected, using the PrtSc key on the keyboard. You will need to reset these settings after you
have upgraded to the latest BIOS. Write down all settings that are unique to the system.
These settings will be needed later to reconfigure the system. Pay special attention to any
hard drive settings; these are very important. If you fail to restore these properly, you may
not be able to boot from the drive or access the data on it.
2. Exit the BIOS Setupand restart the system. Allow the system to fully start Windows and
bring up a DOS prompt window or boot directly to a DOS prompt via the Windows Start
menu (for example, press F8 when you see “Starting Windows,” and select Command
Prompt).
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3. Place a floppy disk in the A: floppy drive and format the floppy using the /S option on the
FORMAT command as follows:
C:\>FORMAT A: /S
4. Alternatively, if you have an otherwise blank preformatted floppy in the floppy drive, use
the SYS command to make it bootable as follows:
C:\>SYS A:
5. The file you originally downloaded from the Intel Web site is a self-extracting compressed
archive that includes other files that need to be extracted. Put the file in a temporary directory, then from within this directory, double-click the BIOS file you downloaded or type
the file name of the file and press Enter. This causes the file to self-extract. For example, if
the file you downloaded was called SEBIOS04.EXE (for the Intel SE440BX motherboard),
you would enter the following command:
C:\TEMP>SEBIOS04 <enter>
6. The extracted files resulting from this should contain a file named BIOS.EXE and a software
license text file. You then do another extract on the BIOS.EXE file to the bootable floppy
you created using the following command:
C:\TEMP>BIOS A:
7. Now you can restart the system with the bootable floppy in drive A: containing the new
BIOS files you just extracted. Upon booting from this disk, the IFLASH program will automatically start; press Enter when prompted.
8. Highlight Save Flash Memory Area to a File and press Enter. Follow the prompts to enter a
filename. This creates a backup of your existing BIOS, which will be valuable should the
new BIOS cause unexpected problems.
9. Highlight Update Flash Memory From a File and press Enter. Follow the prompts to select
the name of the BIOS image file you will use to update the flash ROM. Press the Tab key to
highlight the filename, and press Enter.
10. The system now gives a warning stating that continuing will destroy the current contents
of the flash memory area. Press Enter to continue—the update should take about three
minutes. Do not interrupt this procedure or the flash BIOS will be corrupted.
11. When you’re told that the BIOS has been successfully loaded, remove the bootable floppy
from the drive and press Enter to reboot the system.
12. Press F1 or F2 to enter Setup. On the first screen within SETUP, check the BIOS version to
ensure that it is the new version.
13. In Setup, load the default values. If you have an AMI BIOS, press the F5 key; with a
Phoenix BIOS, go to the Exit submenu and highlight Load Setup Defaults, and then press
Enter.
Caution
If you do not set the values back to default, the system may function erratically.
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14. If the system had unique settings, re-enter those settings now. Press F10 to save the values,
exit Setup, and restart the system. Your system should now be fully functional with the
new BIOS.
Note
If you encounter a CMOS checksum error or other problems after rebooting, try rebooting the system again.
CMOS checksum errors require that you enter Setup, check and save your settings, and exit Setup a second time.
Flash BIOS Recovery
When you performed the flash reprogramming, you should have seen a warning message on the
screen similar to the following:
The BIOS is currently being updated. DO NOT REBOOT OR POWER DOWN until the
update is completed (typically within three minutes)…
If you fail to heed this warning or something interrupts the update procedure, you will be left
with a system that has a corrupted BIOS. This means you will not be able to restart the system
and redo the procedure, at least not easily. Depending on the motherboard, you may have to
replace the flash ROM chip with one that was preprogrammed by the motherboard manufacturer
because your board will be nonfunctional until a noncorrupted ROM is present. This is why I still
keep my trusty ROM burner around; it is very useful for those motherb