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Introduction to Computing
INTRODUCTION TO
Data Storage
CPU AND MICROPROCESSOR
Memory
• Used to store data, instructions, and
information
– The operating system and other system
software
– Application programs
– Data being processed by application programs
• Bytes are stored at specific locations or
addresses
Memory
Memory
• Size of memory is measured by the number
of bytes available
Memory
Memory
• Volatile memory – contents are lost when
the computer is powered down
• Nonvolatile memory – contents are not lost
when the computer is powered down
Memory
Random Access Memory (RAM)
• The memory chips in the system unit
• When the computer starts, operating
system files are loaded from a hard disk
into RAM
Memory
Random Access
Memory (RAM)
• RAM Chips
– Smaller in size than
processor chips
– Packaged on circuit
boards called single
inline memory
modules (SIMMs) or
dual inline memory
modules (DIMMs)
Memory
Random Access Memory (RAM)
• Configuring RAM
– The more RAM, the more programs and files a
computer can work on at once
– Software usually tells you how much RAM is
required
– Necessary RAM depends on what type of work
the computer is used for
Affecting Processing Speed
Virtual RAM
• Computer is out of actual RAM
• File that emulates RAM
• Computer swaps data to virtual RAM
– Least recently used data is moved
5A-30
Memory
Nonvolatile memory
•
•
•
•
Holds data when power is off
Read Only Memory (ROM)
Basic Input Output System (BIOS)
Power On Self Test (POST)
5A-31
Memory
Read-Only Memory (ROM)
• Cannot be modified
• Contents not lost when the computer
is turned off
• PROM
• EPROM
• EEPROM
Bus
Address Bus
Data Bus
Bay
Cache Memory
Helps speed computer processes by storing frequently
used instructions and data
 Also called memory cache
How Computers Process Data
Flash memory
• Data is stored using physical switches
• Special form of nonvolatile memory
• Camera cards, USB key chains
5A-35
Affecting Processing Speed
The bus
•
•
•
•
•
Electronic pathway between components
Expansion bus connects to peripherals
System bus connects CPU and RAM
Bus width is measured in bits
Speed is tied to the clock
5A-36
Teachers Discovering Computers
Integrating Technology
in the Classroom
3rd Edition
Secondary Storage
WHAT IS STORAGE?
 The media on which
data, instructions, and
information are kept
 The devices that
record and retrieve
data, instructions, and
information
 Like a filing cabinet
WHAT IS STORAGE?
Storage Media and Devices
• Storage medium
– Also called secondary storage
– Physical material
• Storage device
– Mechanism used to record and retrieve
– Capacity measured in megabytes or gigabytes
Storage Devices
Floppy Disk
Hard Disk
CD / DVD
Miniature Cards
Smart Cards
Floppy Disks
What is a floppy disk drive?

Device that reads from and
writes to floppy disk



One floppy drive, named drive A
If two floppy drives, second
designated as drive B
Floppy disk drive built into
a desktop computer
Also called secondary storage
External floppy disk drive attaches to
a computer with a cable
p. 7.06 Fig. 7-6
Next
WHAT IS STORAGE?
Floppy Disks
• Portable, inexpensive
storage medium
consisting of a thin,
circular, flexible film
enclosed in a squareshaped plastic shell
• Several sizes
– 8-inch
– 5.25-inch
– 3.5-inch
shutter
shell
liner
magnetic
coating
metal hub
flexible thin film
p. 7.05 Fig. 7-5
Floppy Disks
How does a floppy disk drive work?
Step 1. When you insert the floppy disk into
drive, shutter moves to the side to expose the
recording surface on disk.
Step 6. Read/write
heads read data
from and write data
on floppy disk.
Step 2. When you initiate a disk
access, circuit board on drive that
contains electronics sends signals to
control movement of read/write
heads until they barely touch
surface (film) inside floppy disk’s
shell.
Step 5. Motor
positions read/write
heads over correct
location on recording
surface of disk.
Step 3. For write
Step 4. Motor spins a
instructions, circuit board
verifies whether or not disk
can be written on.
shaft, which causes
surface inside floppy
disk’s shell to spin.
p. 7.06 Fig. 7-7
Next
Floppy Disks
What are tracks and sectors?
Track
is narrow
recording band
that forms full
circle on disk
Click to view Web Link,
then click Floppy Disks
below Chapter 7
p. 7.07 Fig. 7-8
Sector
stores up to
512 bytes
of data
Formatting prepares disk for use and marks bad sectors as
unusable
Next
Floppy Disks
How do you compute a disk’s storage capacity?

Multiply number of sides, number of tracks, number of sectors per
track, and number of bytes per sector

For high-density disk: 2 sides  80 tracks  18 sectors per track  512
bytes per sector = 1,474,560 bytes
Characteristics of a
3.5-inch High-Density
Floppy Disk
Capacity:
1.44 MB
Sides:
2
Tracks:
80
Sectors per track:
18
Sectors per disk:
2880
p. 7.08
Next
WHAT IS STORAGE?
Characteristics of a Floppy Disk
• Uses magnetic patterns to store data
• Formatting
– Track
– Sector
• Write-protection
• Guidelines for floppy disk care
• Floppy disk drive
Floppy Disks
 What is a write-protect notch?
Small opening with a cover that you slide
Protects floppy disk from being erased accidentally


write-protected
notch open
means you
cannot write
on the disk
not write-protected
hole on this
side means
disk is high
density
notch closed
means you
can write on
the disk
p. 7.08 Fig. 7-10
Next
Zip® Disks ®
What is a Zip disk?


Magnetic medium that stores 100 MB
or 250 MB of data or 750 MB
Used to back up and to transfer files

Zip disk
Backup is duplicate of file, program, or
disk in case original is lost
c


Zip disks require a Zip drive — high
capacity drive that reads from and
writes on a Zip disk
REV disks (35GB) are similar.
p. 7.09 Fig. 7-11
c
c
External
Zip drive
Next
WHAT IS STORAGE?
High-Capacity
Removable Disks
• Capacities greater
than 100 MB
• Many uses
– Graphics, audio, or
video
– Transporting files
– Backups
• Zip drive
WHAT IS STORAGE?
Hard Disks
• Provide large storage capacity and high
speed data access
• Sizes range from 30 GB to 100 GB
• Consists of several inflexible, circular disks,
called platters
• Magnetic storage device
• Formatting
Hard Disks
How does a hard disk work?
Step 3.
When software requests
a disk access, read/write
heads determine current
or new location of data.
Step 2.
Small motor spins
platters while
computer is
running.
Step 4.
Head actuator positions
read/write head arms over
correct location on
platters to read or write
data.
Step 1.
Circuit board controls
movement of head
actuator and a small
motor.
p. 7.11 Fig. 7-14
Next
Hard Disks
 What is a cylinder?

Vertical section of
track through all
platters

Single movement
of read/write head
arms accesses all
platters
in cylinder
platter
track
sector
read/write
head
platter
sides
p. 7.11 Fig. 7-15
cylinder
Next
Hard Disk Partitions and
Logical Drives
 When installing an operating system on a new
computer or after recovering from a hard disk
failure, prepare the hard disk for use by:
•
•
•
•
Partitioning the hard disk
Creating logical drives
Formatting logical drives
A maximum of 4 primary partitions can be placed
on a hard disk, but only 1 extended partition
– The way the Master Boot Record is structured
determines this limitation.
Disk Partitioning
Partition disks to divide
total storage space
Primary partition — the
system’s boot drive,
used for system startup
Extended partition —
the remaining drive
space after you create
the primary partition
Logical Disk Drives
A disk partition must
be assigned a logical
drive identifier
A primary partition is
treated as a single
logical drive
An extended
partition can be divided
into multiple logical
drives (drives D and E
in figure)
Logical Drive Format
Low-level format:
• Prepares the hard disk before disk partitions
can be defined
• Primarily the responsibility of the hard disk
manufacturer
High-level format:
• Logical drive formatting that prepares the
drive for use by the operating system
• Creates the file system root directory and
the files used to track disk space use
Hard Disks
What are characteristics of a hard disk?
Sample Hard Disk Characteristics
Advertised capacity
Platters
Read/write heads
Cylinders
Bytes per sector
Sectors per track
Sectors per drive
Revolutions per minute
Transfer rate
second
Access time
40 GB
2
4
16,383
512
63
78,165,360
7,200
100 MB per
actual
disk
capacity
9 ms
Next
p. 7.10 Fig. 7-13
Head Crash on a Hard Disk
 What is a head crash?


Occurs when read/write head touches platter surface
Spinning creates cushion of air that floats read/write head above platter


Clearance between head and platter is approximately two-millionths of an
inch
A smoke particle, dust particle, or human hair could render drive unusable
hair
read/write head
dust
clearance
smoke
platter
p. 7.12 Fig. 7-16
Next
Hard Disk Cache
What is a disk cache?

processor
Portion of
memory that
processor uses
to store
frequently
accessed items
disk cache
first request
for data—to disk cache
in RAM
second request
for data—to HARD
disk
hard disk
p. 7.12 Fig. 7-17
Next
Magnetic Disk Controllers
What is a disk controller?
Chip and circuits that
control transfer of
items from disk
EIDE (Enhanced
Enhanced Integrated Drive
Electronics) controller supports
four hard disks, provides
connections for CD and DVD
drives
p. 364
SATA (Serial
Serial Advanced
Technology Attachment) controller
uses serial signals to transfer data,
instructions, and information
SCSI
(Small Computer System Interface)
controller supports up to fifteen
devices including hard disks, CD
and DVD drives, tape drives, printers,
scanners, network cards
Next
External Hard Disks
What is an external hard disk ?



Used to back up or transfer files
Connects to USB 2.0 or Firewire port
Maxtor One-Touch Backup: 250GB,
Cost: < $200.00 www.Seagate.com
External hard disk—freestanding
hard disk that connects to system unit with
a USB 2.0 cable
p. 7.13 Fig. 7-18
Next
Removable Magnetic Disks
 What are external hard disks and removable hard disks?

Used to back up or transfer files
Removable hard disk—hard disk
that you insert and remove
from hard disk drive
External hard disk—freestanding
hard disk that connects to system unit
Click to view Web
Link, click Chapter 7, Click
Web Link from left
navigation, then click
Hard Disks
below Chapter 7
p. 364 Fig. 7-17
Next
WHAT IS STORAGE?
CDs and DVDs
•
•
•
•
•
Optical storage media
Used to distribute software
Laser reads pits on the surface
Used on multimedia computers
Several types
– CD-ROM
– DVD-ROM
CDs and DVDs
How does a laser read data on a CD or DVD?
disc label
lens
pit
0
prism
lightsensing
diode
Step 1.
Laser diode
shines a light
beam toward
disc.
p. 7.16 Fig. 7-21
laser
diode
lens
land
Step 3.
Step 2.
If light strikes
a pit, it
scatters. If
light strikes a
land, it is
reflected back
toward diode.
1
prism
lightsensing
diode
laser
diode
Reflected light is
deflected to a
light-sensing
diode, which
sends digital
signals of 1 to
computer.
Absence of
reflected light is
read as digital
signal of 0.
Next
CDs and DVDs
How is data stored on a CD or
 Typically stored in
DVD?
single track

Track divided
into evenly
sized sectors
that store
items
Single track
spirals to edge
of disc
The track on a DVD is 7.5 miles
long !
p. 7.16 Fig. 7-22
disc sectors
Next
WHAT IS STORAGE?
Care of CDs and DVDs
• Can last from 5 to 100 years if properly
cared for
• Never bend a disc
• Avoid extreme temperatures and humidity
• Keep away from contaminants
• Do not stack or touch discs
• Use a protective case
WHAT IS STORAGE?
CD-ROM
• Compact disc readonly memory
• Can contain text,
graphics, video, as
well as sound
• Can hold 650 MB of
data
• Used for today’s
complex software
WHAT IS STORAGE?
CD-R and CD-RW
• Compact disc-recordable
– Can write on each part of the disc only one time
– Cannot be erased
• Compact disc-rewriteable
– Can write on multiple times
– Erasable disc
WHAT IS STORAGE?
DVD-ROM and DVD+RW
• Digital video disc read-only memory (DVDROM)
– Can store from 4.7 GB to 17 GB
– High quality
– DVD-ROM drives
– May replace CDs, VCRs, and VHS tapes
• Digital video disc+rewritable (DVD+RW)
– Can write on multiple times
– Erasable disc
WHAT IS STORAGE?
Miniature Mobile Storage Media
WHAT IS STORAGE
External and Removable Hard Disks
• External Hard Disk – Separate hard disk
that connects to a USB or FireWire port by
cable
– USB Drives
File System Types
Primary partitions and logical drives
must be formatted so the operating
system can use them
Formatting creates the file system by
adding information about how files
should be stored on the drive to
organize and manage disk storage
File system types include:
• FAT 16, FAT32 and NTFS (Windows XP)
• Ext3 and ReiserFS (Linux) created by Hans
Reiser
– Note: Hans Reiser was on trial in Feb 2008 for murdering
his wife, Nina Reiser (from Russia). Reiser is/was a
computer programming genius entering Univ California at
Berkeley at age 14
File and Directory Permissions
NTFS allows you to set permission
bits on system resources
In NTFS, you can protect files so that
only certain users or groups of users
can read them
Concerns:
• If permissions are applied improperly,
users may take security for granted
• Improperly set permissions can disrupt
an operating system
Disk Convert Utility
Information about the files on an NTFS
volume and their attributes is stored in
the MFT
Convert utility — used to convert a
partition or logical drive from FAT or
FAT32 to NTFS

convert drive /FS:NTFS
[/v]

convert C:
/FS:NTFS
Disk Convert
Utility
Yes ! It works !
Information about the files on an NTFS
volume and their attributes is stored in
the MFT
Convert utility — used to convert a
partition or logical drive from FAT or
FAT32 to NTFS

convert drive /FS:NTFS
[/v]

convert C: /FS:NTFS
Yes ! It works !
Disk Defragmenter Utility
As files are created and deleted, a
partition can become severely
fragmented
Fragmented files are no longer located
in contiguous clusters
You can use the Disk Defragmenter
utility to defragment hard disks and put
files back together in a contiguous
format
Disk Defragmenter
What is a Disk Defragmenter ?

Reorganizes files and unused space into
contiguous sectors on hard disk so programs
run faster.
file before defragmenting
fragmented disk
file after
defragmenting
p. 8.17 Fig. 8-19
Next
Chkdsk Utility
You can use the Chkdsk utility in
Windows NT/2000/XP to:
• Create and display a status report for a disk
based on its file system
• List and correct errors on the disk
• Display the status of the disk in the current
drive
• Click Start, click Run, type: chkdsk /F,
Click OK
Disk Cleanup
Use the Disk Cleanup utility to recover
the disk space used by:
•
•
•
•
Temporary files
Unused applications
Files in the Recycle Bin
Files you downloaded as part of Web
pages
• Files created when Chkdsk attempted to
recover lost file fragments (e.g.
FILE0001.CHK)
CDs and DVDs
What are CDs and DVDs?



Flat, round, portable
metal discs with
protective plastic
coating
Can be read only or
read/write
Push the button to
slide out the tray.
Insert the disc,
label side up.
Most PCs include CD
or DVD drive, most
play audio CDs
Push the same button
to close the tray.
p. 7.15 Fig. 7-20
Next
Magnetic Tape
How is data stored on a tape?

Sequential access

Reads and writes data consecutively, like music tape

Unlike direct access — used on floppy disks, Zip disks,
hard disks, CDs, and DVDs — which can locate
particular item immediately
Popular Types of Tape
Name
Digital audio tape
Digital linear tape
Linear tape-open
Quarter-inch cartridge
Travan
p. 7. 24 Fig. 7-30
Abbreviation
DAT
DLT
LTO
QIC
TR
Storage Capacity
2 GB to 240 GB
20 GB to 220 GB
100 GB to 200 GB
40 MB to 25 GB
8 GB to 40 GB
Next
PC Cards
What is a PC Card? (thickness is main difference)


Adds capabilities to computer
Credit-card-sized device commonly
used in notebook computers
PC Cards
Category
Thickness
Type I
3.3 mm
Type II
5.0 mm
Type III
10.5 mm
p. 7.24 Figs. 7-31–7-32
Use
RAM, SRAM, flash
memory
Modem, LAN, SCSI,
sound, TV turner, hard
disk, or other storage
Rotating storage such
as a hard disk
Next
Home-Task:
Go through
Chapter 7 of
“Discovering
Computers”
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