Personal Computer Hardware
Personal Computer Hardware
Personal Computer Hardware
Basic Computer (PC)
Main Parts of computer (Hardware)
Input/output Devices
Input Devices
Image / Video Input Devices
Audio Input Devices
Output Devices
Display Devices
Audio Output Devices
Combination of Input and Output Devices
Mother board
Controller cards / Expansion Cards
Secondary Storage
ROM – Read Only Memory
Specification for a Pentium IV PC
Software Components
Computer History and the future
Early Developments
Further Developments and the Development of Languages
Stored Program Concept and Von Neumann Architecture
Modern Trends
Operating Systems
Microprocessor History
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The Computer is a machine.
It is a programmable machine.
It is a multi-tasking system.
i.e. A single machine is used for several different tasks. e.g.:- Word Processing, Designing,
Controlling, Communicating etc.
Those tasks can be done in a single computer simultaneously.
To do these tasks, we may have to attach additional accessories and /or some software to the
basic computer.
e.g.:-for communication - Modem, modem driver and phone dialer
Basic Computer (PC)
The CU (Central Unit)
The Central Unit (CU) is the main part of a computer. All processing, controlling, and storing work is done
in the CU. The user always instructs the CU to get his/her work done.
Input and output devices are used to communicate with the central unit. To instruct the CU the user uses a
key board (an input device). After processing the instructions the CU generally uses the monitor (an output
device) to express its results. Monitor is an essential output device.
Peripherals (input/output)
Mouse - Used to give input signals to computer by clicking left and the right mouse buttons
Keyboard - Used to Display the information
Monitor- Used to Display the information
Speakers - Used to give output s sound
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UPS (Uninterrupted Power Supply)
It is risky to connect your Computer directly to the power source. To protect the
Computer against damages caused by power fluctuations, you use a UPS
(Uninterrupted Power Supply). When you are using a UPS, don’t forget to connect
the power cables of the Monitor and the System Unit to the UPS and can connect the
UPS directly to the power source.
There are ports in the central unit of a computer, which are used to connect the peripherals (input, output
Video port
- 15 pin female connector; There are holes in three rows for a VGA port.
Keyboard port
- Round in shape; Now-a-days PCs have a smaller size port which is called PS/2 type.
Parallel port
- 25 pin female connector; This provides a parallel interface. 8 bit data is send/receive in
parallel. (generally a printer is connected here).
Serial ports
- 25 pin male connector and 9 pin male connector; This provides a serial interface. Data
is sent in serial (bit by bit). Usually Serial ports are used to connect the mouse or
keyboard or external modems ((DB25/9).
Mouse port
- Most of the PCs have a separate port -PS/2 type. (for PS/2 mouse). Some times mouse
is connected to one of the serial port (serial mouse).
USB port
- Universal Serial Bus, a new type of a port available in Pentiums. It is a fast operating
port. Devices having USB adapters such as USB printer, scanner, etc. are connected
Joystick port
- (Game Port) - to connect game elements.
Network port
- BNC or RJ45.
-To connect the Computer to a Network through a Router can use RJ45 connectors.
Mini Jacks
- To Connect the Speakers/Microphone can use Mini Jacks.
Components in the central unit - the computer
Mother board - Where CPU, RAM, Cache, ROM chips with BIOS and start up programs, chip sets
(controllers), ports, buses and expansion slots are available.
Drives - Hard disk(s), floppy drive(s), CD, DVD etc.
Expansion cards - Graphics cards (video adapter), sound card, SCSI controller, network controller,
video and TV card, internal modem.
Cables - Power cables, data cables and indicator cables.
Power supply unit.
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Central Unit - View from back
PS/2 ports
Purple for
& Green
for mice
Orange, purple, or Grey: Keyboard PS/2
Green: Mouse PS/2
Blue or magenta: Parallel Printer DB-25
Amber: Serial DB-25 or DB-9
Pastel pink: Microphone 1/4" stereo (TSR)
Pastel green: Speaker 1/4" stereo (TSR)
Note: Currently (2006) manufacturers have nearly standardized on colors associated with ports on personal computers.
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Secondary storage
In a computer, the processor is the brain. Processor is a miniature wafers of silicon with tiny integrated
circuits and intelligent transistors. Processors are functionally organized into two primary components:
1) A control unit which handles internal operations and directs the software instructions to the proper
elements of the ALU.
2) The ALU which performs the real "computing" -add, subtract, multiply, divide, less than, greater
than and equal functions.
Data Bus
Address Bus
Block diagram of a simple micro-processor
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This is about as simple as a microprocessor gets. This microprocessor has:
An Address Bus (that may be 8, 16 or 32 bits wide) that sends an address to memory
A Data Bus (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from
memory (“B bus” and “C bus” above)
An RD (read) and WR (write) line to tell the memory whether it wants to set or get the addressed
A clock line that lets a clock pulse sequence the processor
Here are the components of this simple microprocessor:
Registers H, LV, CPP and OPC are simply latches made out of flip-flops.
MDR (Memory Data Register), MBR (Memory Buffer Register) and MAR (Memory Address
Register) are just like registers for memory access.
The PC (Program Counter) is a latch with the extra ability to increment by 1 when told to do so, and
also to reset to zero when told to do so.
The ALU (Arithmetic and Logic Unit) could be as simple as an 8-bit adder, or it might be able to
add, subtract, multiply and divide 8-bit values. Let's assume the latter here.
The flag registers (Z and N) are special latches that can be hold the values from arithmetic
operations performed in the ALU. An ALU can normally compare two numbers and determine if
they are equal, if one is greater than the other, etc. The flag registers can also normally hold a carry
bit from the last stage of the adder. It stores these values in flip-flops and then the instruction
decoder can use the values to make decisions.
SP (Stack Pointer) is a special register that can be used to access the stack and the TOS (Top of
Stack) register will hold the top data element of the stack.
The MPC (Micro Program Counter) and instruction decoder are responsible for controlling all of the
other components according to the microinstructions which store in the control store.
Hyper-Threading Technology
Hyper-Threading Technology is a very exciting structure, which can be briefly outlined as follows: In order
to exploit the powerful pipeline in the Pentium 4, it has been permitted to process two threads at the same
time. Threads are series of software instructions. Normal processors can only process one thread at a time.
In servers, where several processors are installed in the same motherboard (MP systems), several threads can
be processed at the same time. However, this requires that the programs be set up to exploit the MP system.
A new feature in Pentium 4 is that it can logically as if there physically were two processors in the PC. The
processor core (with its long pipelines) is simply so powerful that it can, in many cases, act as two
processors. It’s a bit like one person being able to carry on two independent telephone conversations at the
same time.
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The Pentium 4 is ready for MP functions.
Hyper-Threading works very well in Intel’s Prescott-versions of pentium 4. You gain performance when you
operate more than one task at the time. If you have two programs working simultaneously, both putting
heavy pressure on the CPU, you will benefit from this technology. But you need a MP-compatible operating
system (like Windows XP Professional) to benefit from it.
A dual core processor with Hyper Threading operates as virtual quad-processor.
The next step in this evolution is the production of dual-core processors. AMD produces Opteron chips
which hold two processors in one chip. Intel is working on dual core versions of the Pentium 4 (with the
codename “Smithfield”). These chips will find use in servers and high performance pc’s. A dual core
Pentium 4 with Hyper-Threading enabled will in fact operate as a virtual quad-core processor.
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Intel also produces EE-versions of the Pentium 4. EE is for Extreme Edition, and these processors are
extremely speedy versions carrying 2 MB of L2 cache.
In late 2004 Intel changed the socket design of the Pentium 4. The new processors have no ”pins”; they
connect directly to the socket using little contacts in the processor surface.
The LGA 775 socket for Pentium 4.
Memory is the place where data and programs are kept temporarily. There are two types of memory used in
PCs called ROM (Read Only Memory) and RAM (Random Access Memory).
In ROM usually data is written only once and read many time thereafter. This memory is used to store
system-level programs that should be available to the PC at all times. These programs are permanently
stored there. The most common example is the system BIOS program, which is stored in a ROM called the
system BIOS ROM. ROM is fast but expensive.
Memory used for holding user programs and data being executed is called Random Access Memory. RAM
is volatile i.e. when the user turn off the power the information stored in memory is lost. When executing a
program the processor loads the data and instruction needed for processing from secondary storage.
RAM is cheaper than ROM. Usually the amount of ROM in the computer is in the range of kilobytes
whereas the amount of RAM is used in gigabytes.
Input/output Devices
These devices are used to input data to the computer and to get information from the computer. Input/output
or peripheral devices are devices that are connected to the computer, but external in relation to the
processing unit. If you disconnect a peripheral device, the computer will still be able to work; only functions
performed by the removed peripheral device will not be available.
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e.g. If you disconnect a keyboard from the system Unit, it would not be possible to type in information, but
it is possible to work with the graphical user interface by clicking the mouse. Similarly, removing the hard
disk would result in the computer using a floppy disk and to save all the data in floppy disks. So the
computer will be working.
Peripheral devices can reside inside the compute case or outside.
Input Devices
Input device are the hardware used to provide input to the computer that translates words, sounds, images
and actions which people understand into symbols that the system unit process. Input devices include
keyboards, mouse, joysticks, light pens, scanners, digital-cameras, digitizing tablets, and voice recognition
devices etc. Input devices fall in to five categories; Text input, Pointing, Gaming, Image/Video input, and
Audio input.
Text Input Devices
Keyboards convert numbers, letter, and special characters that people understand into electrical signals.
These signals are sent to and are processed by the Central Processing Unit.
A computer keyboard combines a typewriter keyboard with a numeric keypad. There are three types of
keyboards which can be categorized into there different layouts. Those are the QWERTY layout or closelyrelated French AZERTY and German QWERTZ variants.
Modern keyboards distinguish each physical key from every other and report all key presses and releases to
the controlling software. We can categorize all the keys in the keyboard into following categories.
Modifier Keys – Shift, Alt, Ctrl, Windows,
Lock Keys - Num lock, Scroll Lock, Caps Lock
Navigation Keys - Arrow Keys, Page Up/Down keys, Home , End Keys
Edit Keys – Enter, Backspace, Insert, Delete, Tab
PrintAcrn/ SysRq - Pause/Break, Escape, Menu, Space bar, Num pad, Function Keys,
OCR (optical Character Reader) Device
This device recognizes and converts the printed text to computer-compatible file. You can see these devices
mostly used in super Markets to read the prices of the goods. (Bar code Readers).
Mouse is a small hand-held device used to position the cursor, making freehand sketches, or selecting items
from menus on a screen. When the mouse is rolled across the surface of the desk, the cursor moves a
corresponding distance on the screen.
A mouse can have one or more buttons which are used to select command options and to control information
presented on the monitor.
Although several different types of mice are in use, there are three widely using mouse types available.
Mechanical mouse- This mouse has a ball on the bottom and is attached to the system unit via a
cord. According to the movement of the mouse, the roller rotates and controls the pointer on the
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Optical mouse- This mouse has no moving parts and emits and senses light to detect mouse
movements. These mice have some advantages compared to the mechanical mouse. Those can be
used in any surface and need to be cleaned periodically.
Wireless mouse- For this mouse, the power is supplied by the batteries and used radio waves or
infrared light waves to communicate with the system unit. The advantages include free up of desk
space and elimination of mouse cord.
There are three device acting similar like a
Trackball or roller ball – Rotate the
mouse pointer using the thumb to control
the mouse pointer
Touch surface – Rotate the mouse pointer
by moving and taping the finger on the
Pointing stick – Rotate the mouse pointer
by directing the stick using finger
Laser Mouse
These devices are used in Laptop computers, Personal Digital Assistants, etc
Light Pen
This is a light sensitive pen like device. When the light pen is place against the monitor it closes a
photoelectric circuit and identifies the spot for entering or modifying data. Light pens are used to edit digital
This is the most popular input device for compute games. It is possible to control game actions by varying
the pressure, speed and direction of the joystick. Other additional features such as buttons and triggers are
used to specify commands or initiate certain actions.
Image / Video Input Devices
This is used to reproduce text or images. Scanners
record the light and dark areas as well as the
colour of the scanned document. After scanning a
document it is possible to display it on screen, to
print or to store it for later use.
A scanner
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Digital camera
These are similar to traditional cameras but the
images are stored digitally in a disk or in camera’s
memory instead of a film. With a digital camera it
is possible to take a picture and view it
immediately or to put it in a page within few
Digital cameras
Web camera
A web camera is a real-time camera and its
images can be accessed using the World web,
instant messaging, or a PC video application.
Web–accessible cameras typically involve a
digital camera which uploads images to a web
server, either continuously or at regular intervals.
This may be achieved by a camera attached to a
PC, or by dedicated hardware. Videoconferencing
cameras typically take the form of a small camera
connected directly to a PC.
A web Camera
Audio Input Devices
A microphone, sometimes referred to as a mike or
mic, converts sound into an electrical signal.
Microphones are used in many applications such
as telephones, tape recorders, hearing aids, radio
and television broadcasting and in computers for
recording voice, VoIP and numerous other
computer applications. (see Figure)
A Microphone
Digital audio player
A digital audio player (DAP) is a device that
stores, organize and plays digital music files. It is
more commonly referred to as an MP3 player
(because of the format’s ubiquity), but DAPs
often play many additional file formats.
A digital Audio Player
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Output Devices
Output device translate the symbols processed by the system unit in to words, sound, images, and actions
that people can understand. These devices include monitors, printers, and audio – output devices. Basically
we can categorize them as devices, printers and audio output devices.
2.2.1 Display Devices
This is the most frequently used output device. It shows the program or data. There are two important
characteristics of a monitor. They are the size and the clarity. The size of the monitor is indicated by the
diagonal length of its viewing area. e.g.: 15, 17, 19 and 21. Monitor’s clarity is indicated by its resolution,
which is measured in pixels which are individual dots that form images on a monitor. For a given size
monitor the large the resolution the better the clarity of the image. There are two main types of monitors
Cathode Ray Tube (CRT) - The most
common type of monitors in use and
typically placed directly on the system
unit or desktop. These are very similar to
televisions in their size and technology.
Compared with other types CRTs are low
cost and having excellent resolution.
A CRT Monitor
Flat Panel monitors or Liquid Crystal
Display (LCD)- these are developed as a
solution to portable monitors and the
technology involved here are liquid
crystals. These are much thinner than
CRTs. Now the flat panel monitors are to
desktop systems as well.
A LCD Monitor
This output device is used to get the processes information on a paper. We call this printed paper as hard
copies. Ink-jet, laser and thermal printers are the commonly used printers today.
print photos are special purpose ink-jet painters.
Ink-jet Printer- an ink-jet printer sprays small
Among all printers ink-jet printers are the most
droplets of ink at high speed onto the surface of
widely used printers in advertising and public
the paper. This process not only generates a letterrelations.
quality image but also allows printing to be done
in a range of colours. Most photo-printers used to
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and this type is not that expensive. They can
print about four to six pages per minute.
Shared laser printers are little bit expensive
compared to personal laser printers and used
by the group of users. They can print over
thirty pages per minute.
Ink-jet printer
• Laser printer-This uses a technology that
similar to a photocopy machine. Laser printer
uses a laser beam to produce images with
excellent letter and graphics quality. These
are more expensive than the Ink-jet printers
and are used in applications requesting highquality output. There are two categories of
laser printers called personal laser printers
and shared laser printers. Personal laser
printers are used by many single users
A Laser Printer
Thermal Printer – these printers uses heat
elements to produce images on heat–
sensitive paper. Originally these printers
were used in scientific labs to record. But
recently, the colour thermal printers are
used to produce very high quality colour
artwork and text. Compared to other types
these printers are very costly.
A thermal printer
2.2.3 Audio Output Devices
These devices translate audio information from
the computer into sounds that people can
understand. The most widely used types are
speakers and headphones. Audio- output devices
are connected to a sound card in the system unit.
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2.2.4 Combination of Input and Output Devices
Fax machines. Multi-function devices and Internet telephones are examples of this type.
process and prints the document using
• Fax machine – this is also known as
signals received via the telephone line.
Facsimile transmission machine and
currently used in almost every office.
These are separate stand–alone devices
for sending and receiving images over
telephone lines. To send a fax, these
devices scan the image of a document and
converts in to an electronic format which
can be transmitted through the telephone
line to the receiving fax machine. To
A Fax Machine
receive a fax, a fax machine reverses the
Mother board
The motherboard comprises of a processor, provision to fix memory modules, connectors to interface drives,
connectors for ports, buses, the chip set ICs and some other components.
Controller cards / Expansion Cards
Some peripherals and devices are connected to the system through controller cards. These cards are called
adapters. e.g. video adapter.
IRQs, DMAs, and Memory Addresses
There are three things that the CPU uses as communication lines to cards, controller cards. They are IRQs,
DMAs, and base memory addresses.
An IRQ is basically a "stop and do this" message given to the CPU--an interrupt request. For example,
each time you hit a key on your keyboard, the keyboard controller sends an IRQ to the CPU demanding that
it stops and throws down the letter on the screen. Your computer stops what it is doing and follows your
demands. While it does this, it is also handling IRQs from your mouse and various cards.
Base memory addresses are sometimes called I/O ports or port addresses. What are they? Infact CPUs
respond to IRQs. CPUs cannot respond down the same line that it is getting IRQs from. So, a different route
is set up for the responses. It is a kind of go-between so that the CPU and the components can talk directly.
As usual, there are a certain amount of ports available. They usually look something like 02E8, or 03E8.
System Timer
Some video cards
Sound Card
Floppy drive controller
LPT1 (printer port)
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CMOS Clock
Redirected to IRQ2
Math Coprocessor
Hard Drive Controller
There are many software applications which allow you to see which parts are using what IRQs and port
Cards Types
Some common cards are:
Video Cards Everyone has one of these. It allows you to see words on your computer screen. Your
monitor plugs into it.
I/O Cards These are the cards that your printer plugs into (probably your mouse too). These cards
are being phased out; their components are now usually included on motherboards.
Controller Cards This is the card that all of your drives are connected to. A lot of flat ribbons
sprout off of this card. Like the I/O card, this stuff now lives on the motherboard in newer systems.
Sound Cards These cards let your computer produce awesome sound. They are sometimes hard to
install because of IRQ conflicts. In order to hear anything, you need speakers as well. Plug the
speakers into the back of sound cards. The nicer the speakers, the better your sound card will sound.
Modems These allow you to connect to other computers via phone lines. These things are what
bring the Internet to your screen, allowing you to even see this page. Modems are considered tough
to install because they need their own COM port, but I've never had much trouble with it. Also,
modems have two phone jacks on the back of them. One is for the line to the wall, the other is for
you to plug your phone into.
Memory Cards These are used to add more memory to your computer if all of your SIMM slots are
full. This memory will always work slower than the memory in the SIMM sockets because it is
limited to the speed of the bus.
Interface Cards These cards allow you to connect extra gadgets to the outside of your computer.
You can get them for mice, CD-ROMs, scanners, and even adapters for laptop gadgets. If you use
MIDI for a synthesizer connected to the computer, the instrument is connected through an interface
Video Capture Card You can hook a camcorder up to one of these and take pictures off the tape
and save them to your computer. Also, you can buy a TV card. These allow you to watch TV on
your monitor.
Installing Cards
Installing an expansion card is very simple.
1) Turn off the computer, unplug it, and take the case off.
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2) Find the slot that your new card will fit into. The expansion slots are the biggest slots on the
motherboard; sometimes they span the entire width of the board. Your card will plug into one of
them. See if your card is an 8-bit card or a 16-bit card. (If it has one tab, it is 8-bit. If it has two tabs,
16-bit. Three? It is probably a VL-Bus Card.) Stick it in the appropriate slot. You can usually throw
an 8-bit card in a 16-bit slot. You may need to rearrange your cards so that there is room for
3) Remove the dust cover on the back of your computer that is next to the slot you want. Don't lose the
screw; you can use it to hold the card in. Push the card into the slot you chose.
4) Be sure of a few things. Check the card's manual for any jumper settings or other information. This
might save future trouble. Also, make sure that the shiny end with the connector faces toward the
back of the computer. Don't force it in. You might have to play with it a little, but when the card
goes in, you'll know. It will be snug in there. Make sure the card doesn't touch any other cards. That
can cause electrical problems, as you might imagine.
5) Secure the card in place with the screw.
6) Plug the computer back in, turn it on, and install the software that came with the card. This is where
you will find out if all is working right.
Secondary Storage
A program can be directly written on the memory and executed. When the user wants the same program
again another day, the user has to rewrite the program again. Instead, the program can be stored in a place
and called or loaded when it is needed. Secondary storage is used to store data that is not in active use. This
is usually slower than primary storage, or internal memory, but also almost always has higher storage
capacity and is non- volatile, which makes it perfect for the preservation of stored information in an event of
power loss.
A drive is the name for several types of storage media. File system is a method of organizing the files in a
drive. When the drives are formatted, the operating system assigns the file system. During start up, drives
are typically recognized by the PC system software (ROM BIOS + operating system). Thus, the PC knows
which drives are installed. At the end of the start up process the appropriate drive letter is identified with
each drive. If a drive is not "seen" during start up, it will not be accessible to the operating system. However,
some external drives contain special software, allowing them to be connected during operation.
When you start a computer, the microprocessor loads the program from the drives to the memory (RAM)
and executes it.
As secondary storage media can be damaged and files on them become corrupted, it is suggested to make
back-up copies of valuable files on a regular basis. It is essential to check whether the backup copies of the
files are not damaged.
Following are the different types of Secondary storage:
Optical Storage
Floppy Disks
Hard Disks
Flash Memory
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Optical Storage
CD stands for compact Disk. Today’s disks can hold over 17GB of data. Optical disks come in many sizes
including 3 ½, 4 ¾, 5 ¼, 8, 12, and 14 inches. Data is stored in these disks in different ways of different
formats. There are two most common types called CD and DVD.
Compact discs or CDs are the most widely used optical disks today. The typical capacity is about 650MB in
a one side of the CD. The rotational speed is very important because it determines how fast the data can be
transferred from the CD. CD drives are standard on many computer systems. There are three types:
CD-ROM(compact Disc Read Only Memory)
These are used to distribute large software applications, large databases or references.
CD-R (Compact Disc Recordable) also know as WORM (Write Once Read Many)
CD-R is a variation of the Compact Disc which is a write once read only medium (though the whole disk
does not have to be written in one go) and retains a high level of compatibility with standard CD readers
(unlike CD-RW which can be rewritten but has much lower compatibility and the discs are considerably
more expensive).
CD-RW (Compact Disc Re Writable)
This is also known as erasable optical disks
and very similar to other CD-Rs except you
can rewrite to the disk.
The other type of optical disks which are having a greater storage capacity are DVDs or Digital Versatile (or
Video) Disks. The typical capacity is about 17GB.
DVD-ROM (Digital Versatile Disc Read Only Memory)
These are normally used to distribute Movies. For example DVD-ROMs can provide over two hours of
very high quality video.
DVD-R (Digital Versatile Disc
This is similar to a CD-R but higher in
capacity. Also the price is very high
compared to a CD.
DVD-RAM (Digital Versatile Disc Random Access Memory)
DVD-RW (Digital Versatile Disc Re Writable)
DVD-RAM and DVD-RW are two different types of re-usable disks. Like CD-RW, both these two types
of DVDs can be used over and over again. These are used for a wide variety of applications including
the creation and editing of large scale multimedia presentations.
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CD/DVD Players
To read a CD, you need a CD-ROM player. All CD-ROMs conform to a standard size and format, so you
can load any type of CD-ROM into any CD-ROM player. In addition, CD-ROM players are capable of
playing audio, CDs, which share the same technology.
Also to read a DVD, you must have a DVD Player. All DVD-ROMs do accepting a standard DVD size and
format, so you can load any type of DVD-ROM into any DVD-ROM player.
CD /DVD Writers
To write to a CD, you require a CD writer. You
can use it to read the CDs too. But to write a DVD
you need a DVD writer. And it is possible for you
to read DVDs using the DVD writer.
DVD writer
Nowadays most of the CD/DVD Players/ Writers
are coming to the market as a built in component
of the System Unit. But the external CD/DVD
Players/writers are also available; you can
connect these via USB ports to the System Unit.
Floppy Disks
These are also known as diskettes or disks which
are inexpensive removable storage media.
Today’s standard floppy disk is the 1.44MB 3 ½
inch disk. Floppy disks are having a write- protect
notch and when the notch is open the data cannot
be added on the disk. This basically to proceed
protection against accidentally writing over
information on the disk that is useful. There are
three types of floppy disk standards are competing
to become the next standard.
3 ½ Floppy Diskette
Hard Disks
Compared to floppy disks, hard disks are rigid,
faster and provide higher storage. An Internal
Hard Disk (see Figure) is also called a fixed disk
and is located inside the system unit. These are
used to store programs and large data files. Unlike
Internal Hard Disks, Hard-disk cartridges are
removable and can use increase the storage
capacity of the computer system.
Hard Disk
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Flash Memory
Flash memory is a form of non-volatile computer
memory that can be electrically erased and
reprogrammed. Examples of applications include
digital audio players, digital cameras and Mobil
phones. Flash memory is also used in USB flash
drive (thumb drives), which are used for general
storage and transfer of data between computers.
Flash drive
On the mother board the CPU is the “brain”. The buses are the nerve system. The buses can be also thought
as the PC’s express ways. Buses are used to connect CPU to all other components. Physically, they are wires
on the circuit board, which transmit data between different components and they can move one bit at a time.
The system bus
– connects the CPU and RAM.
I/O buses
peripheral bus.
– which connect the CPU with other components. It is sometimes called the
The system bus is the central bus. I/O busses are usually derived from the system bus.
System bus
The system bus is the central bus, which connects CPU with RAM and L2 cache. Other busses branch off
from it. It is designed to match a specific type of CPU. The processor technology determines dimensions of
the system bus and it has taken much technological development to speed up traffic on the motherboard.
It is also called front side bus (FSB) and is a bi-directional data bus. Some computers have an L2 memory
cache external to the CPU connected via a back side bus. This bus and the cache memory connected to it
works faster than accessing the system RAM via the front side bus.
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I/O Bus
I/O buses move data. They connect all I/O devices (drives, monitor, key etc.) with the RAM. Some
computers still use PCI bus and AGP which is used to connect the video to the system. The latest bus is the
PCI express which combine both above functions. I/O buses are really extensions to the system bus. On the
motherboard, the system bus ends in a controller chip, which forms a bridge to I/O buses.
from 1981
Synchronous 8-bit bus which followed the CPU clock frequency of 4.77 or 6
Band width: 4-6 MB/sec.
ISA (PC-AT) Simple, cheap I/O bus.
from 1984
Synchronous with the CPU.
Band width: 8 MB/sec.
from 1987
Advanced I/O bus from IBM (patented). EISA
From 1988
Advanced I/O bus (non-IBM), used especially in network servers.
Asynchronous, 32-bit, at 8.33 MHz.
Band width: 32 MB/sec.
VESA Local Simple, high-speed I/O bus.
32-bit, synchronized with the CPU’s clock frequency: 33, 40, 50 MHz.
from 1993
Band width: up to 160 MB/sec.
from 1993
Advanced, general, high-speed I/O bus. 32-bit, asynchronous, at 33 MHz.
Band width: 133 MB/sec.
USB and
from 1998
Serial buses for external equipment.
PCI Express
from 2004
A serial bus for I/O cards with very high speed. Replaces PCI and AGP.
500 MB/sec. per. Channel.
The PC’s I/O buses, throughout the years
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Introduced in 1990 and is a high speed bus made by Intel. PCI stands for peripheral Component
Interconnect. It is a 32 bit wide bus, but functions like a 64 bit bus. It runs at 33 MHz and maximum
transmission capacity of 132 MBPS. This bus is processor independent. So can be used with all 32 or 64 bit
processors. The PCI bus is buffered in relation to the CPU and the peripheral components. That means, the
CPU can deliver its data to the buffer, and then proceed with other tasks. The bus handles the further
transmission in its own tempo conversely. The PCI adapters can also transmit data to the buffer, regardless
of whether the CPU is free to process them. They are placed in a queue, until the system bus can forward
them to the CPU. Because of this, the peripherals of PCI units operate asynchronously. The PCI bus is
intelligent relative to the peripheral components, in that plug and play is included in the PCI specifications.
All adapter cards for the PCI configure themselves.
Introduced in 1997, it is a new bus for the graphics card. It is called Accelerated Graphics Port. Exclusively
designed for video cards it has better bandwidth for the video system. AGP was introduced with the Pentium
II processor and Intel 82440LX chipset.
Like PCI, AGP uses a 32-bit connector. But, there is a difference. The AGP connector has 64 contacts. AGP
uses a 64-bit wide data path. This extra contact provides new roadways for the pipeline and queue of data
requests. Another difference is that AGP uses an extra eight sideband address lines that allows the controller
to issue simultaneous commands while also accessing all 32 of the main data pathways. This is called
Sideband Addressing, or SBA. All this comes together to give AGP a faster throughput then PCI.
PCI Express
In 2004 a new PCI bus was introduced. The PCI Special Interest Group (see consists of
Intel, IBM, Apple, etc., who coordinate and standardize the bus via this forum. The PCI Express is the
successor to the PCI bus. This is a completely new type of I/O bus using a serial connection (like the buses
USB, Firewire and SATA).
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This new I/O bus will be extremely scalable, as it works with a large number of channels (X1, X2, X16 etc.),
each of which has a bandwidth of about 250 MB/second in both directions, simultaneously.
The standard plans for the use of plug-in cards and devices in various categories, with varying bandwidths
and power consumption. A 16X video card, for example, will totally be able to pull about 8 GB/sec.
PCI Express is based on a serial architecture, making it possible to develop smaller and cheaper devices with
many fewer pins. The new I/O bus will initially co-exist with the PCI interface, as we se it in the
motherboards with Intel i900-series chip sets. But the goal is that PCI Express should replace both PCI and
The two black slots are for PCI Express cards. To the left a 16X card for the graphics controller and to the
right a smaller 1X slot. In-between you see two traditional PCI slots.
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System bus
bus /FSB
Chip set
side bus
RAM is the working memory where data are kept during operation. It is a volatile memory. (It is active
when power is on; i.e. when switch off, data will be lost). Hard disks are non-volatile storage as they retain
memory even when the power is switched off. To process the data in the hard disk, it must be read into
There are two main types of RAM.
Static RAM – Fast, expensive, created using transistors (SRAM)
Dynamic RAM – Slow, cheap, created using capacitors (DRAM)
Further development of the PC and software needed fast memory for some fast operation. So some amount
of static RAM was included in the PC. This memory is called cache memory. This cache memory was
external for CPU (L2 cache).
Later stage it was observed that microprocessor requires same data frequently and it was in external
memory. So microprocessor was spending unnecessary time to take the same data again and again. So
microprocessor needed a storage (fast storage) to keep these frequently used data. That storage is called as
L1 cache. It is built inside the CPU.
RAM technologies
SDRAM – Synchronous Dynamic RAM. This was a new RAM type for PCs. SDRAM is tied to the system
clock and is designed to be able to read or write from memory in burst mode at 1 clock cycle per access(
zero wait states) at memory bus speeds up to 100MHz or even higher. It comes only in 68 bit modules (long
168 pin DIMMS). SDRAM has a access time of only 8-12 ns. This RAM operates at 66MHz, 100MHz and
133 MHz speeds.
Double Data Rate SDRAM -- is similar in function to regular SDRAM, but doubles the bandwidth of the
memory by transferring data twice per cycle-on both the rising and falling edges of the clock signal.
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Rambus DRAM (RDRAM) - The competing standards to replace SDRAM is called Direct Rambus DRAM.
This memory is being designed to use a special type of module called a Rambus Inline Memory Module or
RIMM. This revolutionary design receives a lot of attention because of Intel's decision to pursue this
technology for use in its future chipsets in cooperation with its initial developer, a company named Rambus.
This memory runs at 400, 600MHz or higher.
On a mother board we cannot freely install desired RAM type. The RAM type is controlled by the chip set
of the mother board.
Pentium mother board with SIMMs (Single Inline Memory Module)
On the Pentium mother board, the system bus is 64 bit wide. Therefore, the 32 bit SIMMs are installed in
pairs. Since the standard mother board only has two banks with a total of four SIMM sockets, RAM
expansion possibilities are limited.
Note: Never use different speed RAM modules on the Pentium mother board. All modules must have the
same speed.
Some mother boards have 6 or 8 SIMM sockets. That provides more RAM expansion flexibility.
SDRAM are made in 64 bit wide modules called DIMMs. They have a 168 pin edge connector. Since
DIMM modules are 64 bit wide we can install one module at a time. They are available in 8, 16, 32, 64, 128
and 256 MB with 6, 8, 10 and 12 ns speed. There are usually three DIMM sockets on a mother board.
The advantage of SDRAM is increased speed. That allows to increase system bus speed. With 60 ns EDO –
RAM we can run a maximum of 75 MHz on the system bus, while SDRAM speed can increase to at least
100 MHz. Also the SDRAM work synchronous with the system bus for a better performance.
All new chip sets can control SDRAM. Some mother boards have both SIMM and DIMM sockets. The idea
is that you can choose between reuse EDO RAM in the SIMM sockets, or install SDRAM in SIMM sockets.
It is not designed to mix RAM types though it works in some boards.
A 64 MB DIMM – module holding 32 chips each of 16 M bit (32 x 16 M bit/8 = 64 MB).
RAM technology is being improved. The first attempt to improve RAM speed was the PC 100 standard.
With the chip set like Bx, the system bus speed has come up to 100 MHz. Hence Intel has made a new
standard called PC100. Only 8 ns SD-RAM modules that are constructed according to these standards are
guaranteed to work at 100 MHz.
The new DIMM-modules include a EPROM – chip holding information about the module. The 8 pin little
chip works as a SPD (Serial Presence Detect) – a unit storing information about the RAM type. The idea is
that BIOS can read this information and this way tune the system bus and the timings for a perfect CPURAM performance.
The PC133 RAM is running at 133MHz. It uses 7.5 ns RAM modules. Intel’s new chipset BX2 will support
this PC133.
Rambus (RDRAM) or DDR RAM
The latest or next technology in RAM is called RAMBUS RAM (RDRAM or nDRAM). It is a advanced
technology from an American company 'Rambus'. RDRAM is developed from the traditional DRAM, but
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the architecture has been streamed and optimized to yield new performance. Data is read in packets at a very
high clock speed.
The modules are only 16 bit wide, but they work upto 800 MHz and Giga Hertz will probably follow. All
RAM slots have to be full. This is new, with RAMBUS we have to fill in blank modules in slots which are
not in use.
Another interesting RAM type is the DDR RAM. DDR stands for Double Data Rate: a technology that
transmits data on both sides of a clock signal. DDR-SDRAM is being developed. DDR-SDRAM will be
cheaper than Rambus RAM yet giving the same performance.
A new version of DDR RAM is scheduled for 2003. The new DDR II speeds are 400MHz, 533MHz and
ROM – Read Only Memory
The ROM chips contain the basic/root instructions (System level programs) which are specific for particular
mother board. Those instructions contain instruction for how to work, the setup of the machine, to check the
configuration, and instructions how to start.
All PCs have instructions in ROM chips. There are some special software manufactures who produce BIOS
The primary suppliers are
AMI (American Megatrends)
The adapter ROM
Adapters are expansion cards which are connected to and integrated with the mother board.
On the mother board many technologies are glued together. These technologies are integrated on the mother
board using controllers. They are called the chipset. The chip sets are a bunch of intelligent controller chip,
which are on any mother board.
The controllers are closely tied to the CPU, in that they control the buses around the CPU. Without the chip
sets, neither RAM or I/O buses could function together with the CPU.
When new technological features are introduced, they are accompanied by new chip sets.
Some of the vendors who manufactures these controllers.
- Intel (leader in supplying chip sets to the Pentium mother board.)
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- Cyrix
Popular Chipsets for Pentium IV
Intel 865G
The Intel® 865G chipset, designed to support the Intel® Pentium® 4 processor supporting HyperThreading Technology†, and is a highly flexible and scalable solution that meets a broad range of demanding
computing needs. The 865G chipset offers solid performance through a variety of exciting features,
including dual-channel DDR 400 main memory, an 800 MHz system bus, an integrated graphics controller
with Intel® Extreme Graphics 2 technology, AGP8x Graphics and Hi-Speed USB 2.0.
Intel 915G Express
The Intel® 915G Express chipset, designed for the Intel® Pentium® 4 processor supporting HyperThreading Technology† in the LGA775 package, delivers a decade's worth of innovation:
PCI Express* buses can deliver over 3.5 times more bandwidth for I/O and graphics cards than PCI
and AGP 8X respectively1.
Graphics flexibility, with support for the built-in Intel® Graphics Media Accelerator (GMA) 900
and for PCI Express graphics cards
Flexible memory support for dual channel DDR2 533 memory and dual-channel DDR memory
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800/533 MHz system bus Front Side Bus (FSB) support for high-performance Intel® processors and greater
system performance.
Supports HyperIncreased system responsiveness for multi-tasking.
Threading Technology†
LGA775 socket
LGA775 socket supports the highest performance Intel® desktop processors.
Intel® Graphics Media
Stunning media, incredible visuals and new 3D capabilities. For business users, Intel
Accelerator 900 (Intel® validates the chipset, processor, graphics and software stack to provide a well-tested
GMA 900 graphics)
platform with support for Microsoft* Windows 2000, Windows* XP, Linux (top
distributions) and OS/2 (SciTech).
PCI Express* bus
PCI Express* x16 graphics delivers up to 4 GB/s per direction, 3.5 times more
bandwidth than AGP 8X. PCI Express x1 I/O offers 500 MB/s concurrently, over 3.5
times more bandwidth than PCI at 133 MB/s.
Dual-channel DDR2 or
Direct Media Interface
Intel® High Definition
Flexible memory support, for dual-channel DDR2 533/DDR2 400 or DDR400/DDR333
memory, in configurations of up to 4 GB RAM.
For I/O intensive applications, new serial point-to-point bus delivers up to 2.0 GB/s
concurrent bandwidth between the memory and I/O controllers, compared to 266
MB/s with previous generation Intel® hub architecture.
Support for new consumer entertainment formats such as 7.1 surround sound,
Dolby* Digital, and DTS*. Audio codec support for 192 kHz quality, multiple streams,
and better voice input for speech recognition and voice-over-IP.
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Intel® Matrix Storage
Boosts storage performance with RAID 0, while protecting your digital memories with
Technology with ICH6R or RAID 1, on the same disks. Advanced Host Controller Interface (AHCI) further boosts
RW only
performance with Native Command Queuing (NCQ), and provides native hot plug for
drive swaps.
Four Serial ATA ports
Integrated serial ATA controller facilitates high-speed data transfers at up to 150
MB/s for each of four ports. Allows easier hard drive upgrades and expansion for new
SATA optical drives.
Ultra ATA/100
Supports legacy hard drives and optical drives.
High-speed USB 2.0 Ports Eight ports offer up to 40X greater bandwidth over USB 1.1, for high-speed I/O
peripherals such as digital video cameras.
Intel Serial Digital Video Dual SDVO ports offer maximum display (digital CRT or TV) flexibility through the
Output (SDVO) ports
existing PCI Express* x16 connector.
Intel 945G Express
For Intel® Pentium® D Processor and Intel® Pentium® 4 Processor supporting HT Technology
Built-in Intel® GMA950 graphics
Intel® Flex Memory Technology
Dual channel DDR2 667/533/400
PCI Express* X16
Intel® HD Audio
PCI Express X 1 (4or6³)
Serial SATA 3Gbps/4
Intel® Matrix Storage Technology (NCQ, RAID 0, 1, 5, 10)
Intel 965G Express
For Intel® Core™2 Duo processor, Intel® Pentium® D processor, Intel® Pentium® 4 processor supporting
Hyper-Threading Technology and all other Intel® processors using the LGA775 socket
1066/800/533 MHz 2 threads
Intel® Fast Memory Access
PCI Express* x16
Intel® Graphics Media Accelerator 3000
Intel® High Definition Audio
Intel® Matrix Storage Technology4 (NCQ, RAID 0, 1, 5, 10)
Intel® Active Management Technology5
Dual channel DDR2 800/677/533
Intel® Quiet System Technology
Intel® Flex Memory Technology
USB* Port Disable
Intel 975X Express
For Intel® Pentium Processor Extreme Edition
1066/800 MHz FSB
Intel® Memory Pipeline Technology
Dual channel DDR2 667/533
Up to 8GB memory support
PCI Express* x16 and x1
Serial ATA 3Gbps
Intel® Matrix Storage Technology (RAID 0, 1, 5, 10)
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Specification for a Pentium IV PC
Motherboard - (ATX/LGA/800/Intel i915G for Pentium IV processor)
This motherboard has two independent high performance bus mastering PCI EIDE interfaces capable of
supporting up to Ultra DMA/ATA-100 devices and SATA Drives. The system BIOS supports automatic
detection of the EIDE device data transfer rate and translation between different kinds of device modes such
as Logical Block Addressing (LBA), Extended cylinder sector Head (ECHW) translation modes and ATAPT
(E.g.: CD-ROM) devices on both EIDE interfaces. Motherboard has two high speed serial ports, one parallel
port (supporting ECP and EPP standards), two USB ports and provision to install DDR II modules.
Motherboard's Chipset is Intel i915G and 800MHz system bus speed.
Intel Pentium IV LGA processor with 3.06 GHz Clock speed and HT technology & suitable cooling system
Built in Math coprocessor; 512 KB L2 CPU cache at full processor speed. Processor
system bus speed.
supports 800 MHz
512 MB PC4200 DDR-RAM module
PCIe x16 Video card with 64 MB memory.
EIDE Hard disk minimum 80 GB (Ultra DMA/ATA-100 or SATA ).
52X IDE CD drive State the Brand name
1.44MB Floppy drive
10 / 100 MBPS Ethernet network card with UTP and BNC connectors,
Full tower case with about 450W for P4 LGA, ATX power supply, with built in over load/surge.
2.5 Software Components
The ROM chips contain the basic/root instructions (System level programs) which are specific for particular
mother board. Those instructions contain instruction for how to work, the setup of the machine, to check the
configuration, and instructions how to start. We can differentiate them as follows.
POST (Power on Self Test).
The setup instructions, which connect with the CMOS instructions.
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BIOS instructions, which connect with the various hard wave peripherals.
The boot instructions, which call the operating system (DOS, Windows, Unix)
All these instructions are in ROM chips and they are activated one by one during start up.
When a machine is started up it first does the POST (The test programs). Then the initializing routine sets up
the BIOS functions. The adapter ROM is integrated (A table covering all the BIOS programs is constructed.
This is called the interrupt vectors). At last it look for the bootstrap routine which calls upon the Operating
The BIOS programs
Basic input output system are programs which are linked to specific hardware systems. During start up the
BIOS programs are read from a ROM chip loaded to the memory (input output area)
e.g.: There is a BIOS routine, which identifies how the PC reads input from the keyboard.
The BIOS programs control hardware, user/programming controls hardware via a call to BIOS. BIOS
typically occupy IMB and saved in ROM chips on the mother board.
This is the first instruction executed during startup. It checks the PC components and whether everything
works. E.g. RAM test. The order is basically;
1) Information about the graphics adapter.
2) Information about the BIOS (name, version)
3) Information about the RAM (being counted)
A user has only limited ability to manipulate. Only can instruct for a quick check or Esc to disrupt. This test
detects errors in the system and given the message.
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E.g.: 3 short and one long beep, when there is a error in video card.
There is a small amount of memory maintained with electric power in a CMOS (Complimentary Metal
Oxide Semiconductor) with a small battery. It holds important system data, values to be used during the start
process. This information may be about 100 or 200 bytes of data instantly available to the POST and BIOS
programs (loaded from ROM) during the start up.
Some of those values are floppy, hard disk drive parameters, keyboard, CPU, cache, chipset values, RAM
types, Date and time. These data have to be set correctly and once read during start up. Floppy drives and
IDE hard disks are so ‘dumb’ they need too be specified. While EIDE hard disk are little more intelligent,
however POST needs assistance to identify them 100% correctly, POST can count how much RAM is
available but cannot detect whether it is FPM, EDO or SDRAM (type).
The PC must be configured with this information. This is done in the factory where it is assembled. When
different or additional hardware components are installed, it needs to be updated. There are some parts for
user options in CMOS. E.g.: date, time, boot sequence etc.
Many of the options are of no interest to the ordinary user. The mother board manufacturer has already
selected them to the optimal configuration – default settings.
User communicates with the BIOS programs and the CMOS memory through setup program. User interface
for these programs will appear based on the BIOS program manufacturer (AMI, Award, etc).
The standard values
The date & time
- values are stored in the CMOS ROM.
Can be changed using setup or from operating system.
The keyboard
- it obviously has to be there. PC can be configured to work without keyboard.
The display
- default is VGA. Options are available for EGA, CGA, MDA.
Diskette drive
- Drive have to be selected correctly. (1.44 MB or 1.2 MB)
Note: Modern super floppies like Zip and LS120 are not to be installed as diskette drives. They are EIDE
The hard disk
- most important unit to setup. The modern mother board and EIDE drives have
automatic configuration. (Auto detect)
In early systems cylinders, heads and sectors need to be set correctly.
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The BIOS feature setup is the second layer in the CMOS setup.
Quick execution of POST
Choice of boot device EIDE/SCS1 (if both available)
The boot sequence
Power management
Password protection ( to erase password – remove battery)
The chip set feature setup needs no changes generally. It relate to the chip set.
The adapter ROM
Adapters are expansion cards which are connected to and integrated with the mother board. They have BIOS
codes in there. The adapters hold their own BIOS code making them functional. These adapter ROM is read
during startup and the program code is moved together with other BIOS programs and the CMOS data. It is
all written into RAM, where it is ready for the operating system. The BIOS routines are regarded as basic
program layers in the PC. Many programs routinely by pass BIOS, they “write direct to hardware”.
e.g.: com port access in windows.
In the modern mother boards BIOS instructions are in flash ROM, which can be updated, these up dates are
available from the supplier.
The new mother board (ATX) BIOS program continually checks the CPU temperature and voltages, the
cooling fan RPM, etc. If over heating occurs, the PC will shut down automatically. The new PC can also be
turned on by, for example modem signals, since the power supply is controlled by mother board.
Early Developments
The Abacus
Abacus is a calculation tool, often constructed as a wooden frame with beads sliding on wires. The standard
abacus can be used to perform addition, subtraction, division and multiplication; abacus can also be used
extract square-roots and cubic roots.
Abacus is still used today by shopkeepers some Asian and African countries. Blind children are taught to use
the abacus where their sighted counterparts would be taught to use paper and pencil to perform calculations.
Charles Babbage’s Analytical Engine
A British scientist called Charles Babbage designed the analytical engine. He started developing it in 1834
and the trial model has first come out in 1871. In the same year Babbage died.
The Analytical Engine was not only automatic but also general purpose; i.e. it could be ‘programmed’ by the
user to execute a range of instructions in ant required order. The engine was programmable using punched
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Census and Punch Card Machinery
The punch card (or “Hollerith” card) is a recording medium for use by automated date processing machines.
Made of thin cardboard, the punch card represents information as the presence or absence of holes in
predefined positions on the card. In the first generation of computing, from the 1920s into the 1950s, punch
cards were the primary medium for data storage and processing. Eventually, during the late 1970s to early
1980s, the punch card was phased out as a medium for storage of computer data and was replaced by huge
floppy disks.
Turing Machines
In 1936 Alan Turing introduced his machine and established its basic properties so that it can perform a
computational task. Turing defined his machines to consist of following basic properties.
A finite set, of possible states
A potentially infinite tape, consisting of consecutive cells
A read/write tape head etc.
The beauty of Turing machines is that the model is extremely simple, yet nonetheless, extremely powerful.
A Turing machine has potentially infinite work space so that it can process arbitrarily large inputs, e.g.,
multiply two huge numbers, but it can only read or write a bounded amount of information, i.e., one symbol,
per step.
Atanasoff-Berry Computer (ABC)
The Atanasoff-Berry Computer, sometimes referred to by its initials, ‘ABC’ was invented in 1938-42 at
Iowa State University, by Dr. John Vincent Atanasoff and Clifford E. Berry. It was used to solve
simultaneous linear equations. It was made of vacuum tubes and was about the size of a desk.
This machine was described as the first electronic digital computer because of its use of electronics for
arithmetic calculations.
This machine featured three main characteristics if a modern computer:
The use of binary digits to represent data
Performing all calculations by using electronics.
Having a system in which computations and memory were separated
It also used regenerative capacitor memory.
Zues’s Computing Machines
In 1934 Konrad Zuse discussed the question “What mathematical problems should a computing machine
solve?” His answer was the following definition of computing (1936): “To build new specifications from
given specifications by a prescription”.
With this, and later extended definitions, Konrad Zuse designed the architecture of his computers Z1, Z2, Z3
and Z4. according to him, his computers should be free-programmable, meaning that they should read
arbitrary instructions from a punch tape and they should work in the binary digit system because Zuse
wanted to construct his computer with binary switching elements. Not only the numbers be represented in
binary form, but the whole logic of the machine should work in a binary switching mechanism (0-1
principle). He built a high performance floating point processor in the semi-logarithm representation, which
was allowed to calculate very small and very big numbers with sufficient precision.
He implemented a performance adder with a one-step carry and a precise arithmetic exceptions handling. He
constructed a control unit, which controlled the whole machine, and implemented input-and output devices
in the decimal number system
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The ENIAC (Electronic Numerical Integrator and Computer) was invented in 1943 by Professor “Mouchly”
and one of his students named “Ecller”, at the University of Pennsylvania. This was a general purpose
computer, built using vacuum tubes and a large machine, weighing about 30Tons and it occupied 1,500
square feet of floor space.
The ENIAC was a decimal machine. Since numbers and arithmetic calculations were represented in decimal
form, its memory was made of 20 “accumulators”. Each of these were capable of storing a 10 digit number.
The ENIAC had to be programmed manually by setting switches and plugging/ unplugging cables. Hence,
this was the main drawback of the ENIAC.
The Colossus Computer
An engineer called Tommy Flowers invented the Colossus computer. This was used by British code breakers
to read encrypted German messages during the world war II. Colossus Computer was one of the earliest
electronic digital computers. A prototype of this computer, namely colossus Mark was in operation in 1944.
It contained only 1,500 electronic valves, where as the early stored program computers used about 4,00018000 electronic valves.
Further Developments and the Development of Languages
By the 1940s, the switching units in computer were mechanical relays which were then replaced by vacuum
tubes. These vacuum tubes soon turned out to have critical disadvantages which impeded the further
progress in computing technology.
After the transistor was invented, scientists were attempting to figure out the smallest size for the transistor,
since it should be connected to wires and other electronics. Hence there was a requirement to build a whole
circuit (e.g.: the transistors, wires, etc) in a single unit. This integration of a large number of electronic
components onto a single chip was great achievement over the manual assembly of vacuum tubes and
circuits using discrete components.
Since a communication medium was needed to communicate with the computer, scientists faced the
challenge of developing a language that could be used as a communication medium to program the
The first generation language was called machine language or machine code. This code consisted of
sequences of 0’s and 1’s which the computer electrically interprets as instructions. But this code language
proved to be complex, difficult to understand, and error prone.
To overcome the above mentioned difficulties, scientists emerged with the 2nd generation language in the
early 1950s. This was a set of mnemonic words which replaced sequence of 0’s and 1’s in machine code
(e.g.: A for “add”, M for “multiplies’). These mnemonics were translated in to machine code by computer
program called the Assembler. But the resulting machine code was specific to a particular type of computer,
and would not run on a Computer with a different type of a central processing Unit (CPU).
The problems created by the low level languages, prompted scientists to emerge with a new concept: High
level Language. These languages were portable between different computers, as it ignored many of the low
level language characteristics. They were also much closer to natural languages, and were translated into
machine code by using a program called a compiler or interpreter. Thus, these 3rd generation languages
caused programmers to create computer program which were less prone to errors.
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Stored Program Concept and Von Neumann Architecture
The ENIAC was used to do basic mathematical calculations. It was not used for word processing or to run
video games. These computers worked based on fixed programs. Entering programs or altering Programs for
the ENIAC was extremely tedious. If program alteration was required, the machine had to be re- designed.
As a solution the ‘Concept of stored Program’ was introduced. Here, the program itself was stored in the
computer’s memory, along – side with the data. Hence, the computer reads the instructions required to
perform a specific task from its own memory. If a program was required to be altered, it could be done by
altering the values of only a portion of the memory. Hence, the term ‘Programming the Computer’ became
popular in the computer industry.
This idea was first executed on a computer named EDVAC (Electronic Discrete Variable Computer), by
Von Neumann in 1945. In 1946, Von Neumann and his colleagues began the design of the IAS computer,
which also worked according to the ‘Stored Program concept’, at Prince Top Institute. This design was
completed in 1952, and was followed by all subsequent computers which used the same ‘stored program
IAS computer contained,
A main Memory, which stores both Data and Instructions
An Arithmetic and Logic Unit (ALU) capable of operating on binary data
A control Unit, which Interprets the instructions in memory and causes them to be executed
Input and Output (I/O) equipments operated by the control unit.
The memory of the IAS consists of 1000 storage locations called ‘Words”, of 40 binary digits each, which
also contains the data and instructions. Hence data and instructions both have to be represented in binary
Each number is represented by a sign bit and a 39-bit value. A word may also contain two 20-bit
instructions, which each instruction consisting of an 8-bit operation code (op-code) specifying the operation
to be performed and a 12-bit address designating one of the words in memory (numbered from 0 to 999).
Modern Trends
VLSI Technology and the 4004 Chip
VLSI (Very Large-Scale Integration) as its name implies, this is the integration of the maximum possible
number of logic devices in to a minimum amount of space. This technology has made possible the use of
many of our day–to-day equipments such as cell phones, cameras, computers, etc.
With VLSI technology, the capabilities of an IC have increased over the years. Hence, ICs are now used for
many diverse applications in day to day objects (e.g.: even the shoes that we wear could be used to monitor
our heartbeat).
VLSI designs could be classified into three categories:
Small transistor count precision circuits such as Amplifiers, Data Converters, Filters,etc.
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Operating Systems
Some years ago an operating system was defined as the software that controls the hardware, but the
landscape of computer systems has evolved significantly. Since then, requiring a more complicated
description to increase hardware utilization, several applications were designed to execute concurrently. As a
result, a layer of software called an Operating system (OS) is separated from the application software.
When a user requests that the computer perform an action, the OS manages the software and hardware to
produce the desired result. Operating systems are primarily resource mangers- they manage hardware,
including processor, memory, input output devices and communication devices, so ultimately the OS job is
to manage all these devices and provide user programs with a simpler interface to the hardware.
The Functions of an Operating System
The scheduling and loading of programs or subprograms, in order to provide a continuous sequence
of processing or to provide appropriate responses to events
Control over hardware resources, e.g.: control over the selection and operation of devices used for
input, output or storage
Protecting hardware, software and data from improper use
Provision of error correction routines
Modern computer operating systems may be classified into three groups namely Batch processing, Time
sharing, and Real time operating systems.
Batch processing operating system
In a batch processing users submit jobs to a central place where these jobs are collected into a batch, and
subsequently placed on an input queue at the computer where they will be run. In this case, the user has
no interaction with the job during its processing, and the computer’s response time is the turnaround
time- the time from submission of the job until execution is complete, and the results are ready for return
to the person who submitted the job.
Time Sharing Operating systems
In this environment a computer provides computing services to several users concurrently on-line. Here,
the various users are sharing the central processor, the memory, and other resources of the computer
system facilitated and controlled by the operating system. The user, in this environment, has nearly full
interaction with the program during its execution, and the computer’s response time may be expected to
be no more than a few seconds.
Real time operating systems
Examples of real time operating systems are those which handle airline reservations, machine tool
control, and monitoring of a nuclear power stations. The systems, in this case, are designed to be
interrupted by external signal that require the immediate attention of the computer system.
Microprocessor History
A microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine
that is fabricated on a single chip. The first microprocessor was the Intel 4004, introduced in 1971. The 4004
was not very powerful -- all it could do was add and subtract, and it could only do that 4 bits at a time. But it
was amazing that everything was on one chip. Prior to the 4004, engineers built computers either from
collections of chips or from discrete components (transistors wired one at a time). The 4004 powered one of
the first portable electronic calculators.
Personal Computer Hardware
The first microprocessor to make into a home computer was the Intel 8080, a complete 8-bit computer on
one chip, introduced in 1974. The first microprocessor to make a real splash in the market was the Intel
8088, introduced in 1979 and incorporated into the IBM PC (which first appeared around 1982). If you are
familiar with the PC market and its history, you know that the PC market moved from the 8088 to the 80286
to the 80386 to the 80486 to the Pentium to the Pentium II to the Pentium III to the Pentium 4. All of these
microprocessors are made by Intel and all of them are improvements on the basic design of the 8088. The
Pentium 4 can execute any piece of code that ran on the original 8088, but it does it about 5,000 times faster!
The following table helps you to understand the differences between the different processors that Intel has
introduced over the years.
Transistors Microns
2 MHz
8 bits
5 MHz
16 bits
8-bit bus
6 MHz
16 bits
16 MHz
32 bits
25 MHz
32 bits
60 MHz
32 bits
64-bit bus
Pentium II
233 MHz
32 bits
64-bit bus
Pentium III
450 MHz
32 bits
64-bit bus
Pentium 4
1.5 GHz
32 bits
64-bit bus
Information about this table:
• The date is the year that the processor was first
introduced. Many processors are re-introduced at higher
clock speeds for many years after the original release
• A transistor is the number of transistors on the chip.
You can see that the number of transistors on a single
chip has risen steadily over the years.
• A micron is the width, in microns, of the smallest
wire on the chip. For comparison, a human hair is 100
microns thick. As the feature size on the chip goes
down, the number of transistors rises.
Clock speed is the maximum rate that the chip can
be clocked at. Clock speed will make more sense in the
next section.
Data width is the width of the ALU.
numbers, while a 32-bit ALU can
manipulate 32-bit numbers. An 8-bit ALU
would have to execute four instructions to
add two 32-bit numbers, while a 32-bit
ALU can do it in one instruction. In many
cases, the external data bus is the same
width as the ALU, but not always. The
8088 had a 16-bit ALU and an 8-bit bus,
while the modern Pentiums fetch data 64
bits at a time for their 32-bit ALUs.
MIPS stands for "millions of
instructions per second" and is a rough
measure of the performance of a CPU.
Modern CPUs can do so many different
Personal Computer Hardware
things that MIPS ratings lose a lot of their meaning, but
you can get a general sense of the relative power of the
CPUs from this column
What's a Chip?
A chip is also called an integrated
circuit. Generally it is a small, thin
piece of silicon onto which the
microprocessor have been etched. A
chip might be as large as an inch on a
side and can contain tens of millions of
transistors. Simpler processors might
consist of a few thousand transistors
etched onto a chip just a few
Personal Computer Hardware
A device that Works under the control of stored programs,
automatically accepting, storing and processing Data to
produce Information that is the result of that processing.
Consist of Data and Instruction
Processed Data or Information.
Raw fact (un processed facts including text, numbers,
images, and sounds.)
Processed Data.
Converting Data in to Information.
Serial Port
Used to connect Monitors, LCDs, (sometimes Mouse and
keyboard) to the System Unit.
Parallel Port
PS/2 Port
Used to connect Printers to the System Unit.
Used to Connect Mouse and the Keyboard to the System
RJ45 Connector
Used to connect Computer to a network.
Rj12 Connector
Used to connect Computer to the Internet through the
Telephone line.
Mini Jack
Used to connect speaker and the Microphone to the System
USB Port
Universal Serial Bus. Used to connect Several external
devices without inserting cards for each device.
Input Devices
Output Devices
Connecting sockets.
Used to input data to the Computer.
Used to output information from the Computer.
Convert numbers, letters, and special characters that people
understand into electrical signals.
Recognizes and converts the printer text to computer
compatible files.
A small hand-held device used by to positioning the cursor,
making freehand sketches, or selecting items from menus
on a screen.
Track Ball
(Roller Ball) Rotate the mouse pointer using the thumb to
control the mouse pointer.
Touch surface
Rotate the mouse pointer by moving and taping the finger
on the surface.
Pointing Stick
Rotate the mouse pointer by directing the stick using finger.
Touch Screen
A monitor screen covered with a plastic layer which has
crisscrossed invisible beams of infrared light, allows to
Personal Computer Hardware
touch the screen using a finger and to select the respective
actions displayed on the screen.
Light pen
Used to edit digital images.
It is possible to control game actions by varying the
pressure, speed and direction of the joystick.
Used to reproduce text or images.
Digital Camera
Digitizing Tablet
Web Cam
Images are stored digitally in a disk or in camera’s memory
instead of a film.
Converts sketches or figures in to a form that can process
by a computer.
A real – time camera whose and its’ images can be accessed
using the world Wide Web, instant messaging, or a PC
video calling application.
Converts sound into an electrical signal.
Digital Audio
A device that stores organizes and plays digital music files.
A device which is similar to a television screen which
allows you to see the program or data.
(Cathode Ray Tube) Type of Monitors used to display
processed information on the screen.
(Liquid Crystal Display) Flat Panel Monitors used to
Display processed information on the screen.
Used to get the processes information on a paper.
Translate audio information from the computer into sounds
that people can understand.
Fax Machine
(Facsimile transmission) Separate stand-alone devices for
sending and receiving images over telephone lines.
Multi Function
Combines the capabilities of a Scanner, printer, fax and a
photocopy machine.
Internet Telephony
Uses the internet to connect multiple people via telephone.
Secondary Storage
(External memory) Kind of a computer memory that is not
directly accessible to the central processing unit of a
Compact Disk is an optical disc used to store digital data.
Compact Disc Read-Only Memory is a compact disc that
contains data accessible by a computer.
Compact Disc –Recordable is a variation of the Compact
which is a write once read only medium.
Compact Disc Re-Writable is a rewritable optical disc
Digital Versatile Disk or Digital Video Disk has a more
Personal Computer Hardware
storage capacity than a CD.
Digital Versatile Disk Read-Only Memory is a optical disc
that Contains data accessible by a computer, but has higher
capacity than a CD-ROM.
Digital Versatile Disk Random Access Memory has built-in
error control and a defect management system.
Digital Versatile Disk Recordable similar to a CD-R but
higher in Capacity.
Digital Versatile Disk Re- Writable is a re-writable optical
disc with equal storage capacity to a DVD-R.
Floppy Diskette
A data storage device that is composed of a disk of thin,
flexible (“floppy”) magnetic storage medium encased in a
square or rectangular plastic shell.
Zip Disk
A medium – capacity removable disk storage system.
Super Disk
A series of floppy disk drives which has a higher capacity
than a Floppy disk.
A disk which is similar to a Floppy drive but has a higher
storage capacity.
Hard Disk
A disk which is located inside the system unit and use to
store programs and large data files.
Flash Memory
This is a form of non-volatile compute memory that can be
electrically erased and reprogrammed.
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