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Actually a Computer by itself is nothing like a calculator or typewriter but it is the collection of many parts. After assembling many parts we are able to use Computer.
Each and every part of Computer has its own specialty. Some parts of Computer play very important role in our Computer system and without them, we are unable to use Computer but some are used to add extra functionality to our Computer and we are able to use Computer without them.
Normally every PC is based on the following parts:
1) Monitor
2) System Unit
3) Keyboard
4) Mouse
5) Printer
We compare two Computers according to speed, capacity and components.
Internal Parts / Devices
Parts of Computer, which are inside the system unit, are called internal parts or internal devices.
External Parts / Devices
Parts of Computer outside the system unit are called external parts or external devices.
Monitor
It is an output device which looks like a TV screen. It provides visual reports of Computer’s operation. It can display 25 x 80 characters at a time, i.e. 25 Rows and 80 Columns.
Different types of ‘Adapters’ (Cards) support monitor. e.g.
· CGA (Color Graphic Adapter)
· EGA (Enhanced Graphic Adapter)
· VGA (Video Graphic Adapter)
· SVGA (Super Video Graphic Adapter)
System Unit
It is one of the major parts of Computer system. It is consisted upon motherboard, C.P.U, memory, disk drives, power supply unit, cards etc.
Motherboard (Mainboard)
It is actually a printed circuit board. All important parts e.g. C.P.U, memory, expansion slots (buses) are fixed on it.
Every part of Computer e.g. monitor, keyboard, mouse, etc. are connected to Motherboard with special cables.
Microprocessor
It is the brain of Computer. It interprets the instructions, perform calculations and transfer data from one place to another as specified in the program. It contains the electric circuits and transistors, which actually causes processing to occur. It also controls the input-output (I/O) operations of the system.
Processor has two main units:
1) BIU (Bus Interface Unit)
2) EU (Execution Unit)
1) BIU (Bus Interface Unit)
It interfaces other components and data it also transfers the data to other units of Microprocessor for further processing.
2) EU (Execution Unit)
It executes the data after processing and gives it back to BIU.
Main Computer Storage (Memory)
The place where our data is stored in Computer is called memory.
ROM (Read Only Memory)
It is a type of memory that can be read but cannot be changed. Thus the information stored in this memory are of permanent nature. These informations were stored in this memory at the time of its construction. Simple ROM was used when Computer technology was not so advanced. Material stored in ROM is not effected by power failure. ROM cannot be used as our regular storage media.
ROM is of three types:
1) PROM
2) EPROM
3) EEPROM
1) PROM (Programmable Read Only Memory)
These kinds of ROMs are called programmable ROMs. PROM is ROM in which the user can load Read Only Programs and data. The contents of PROM are usually loaded with special purpose program. And the user or programmer can also change it when it is required.
2) EPROM (Erasable Programmable Read Only Memory)
These kinds of ROMs are very advanced because the contents of EPROM can be erased and can be reprogrammed when required, with the help of special device (ultra-violet rays).
3) EEPROM (Electrically Erasable Programmable Read Only Memory)
It is just like EPROM but is does not require ultra-violet rays for erasure. It is erasable by electric pulses.
The main duty of ROM, PROM, EPROM and EEPROM is to check the components of Computer after turning it ON which is known as POST (Power On Self Test). If there is any failure (any part of Computer is disconnected or damaged) found during POST they are indicated by error code or beep(s). If ROM doesn’t find any failure during POST then it starts loading the operating system files from a bootable disk into Computer’s main memory (RAM) for further use.
RAM (Random Access Memory)
RAM is the primary memory of Computer. It is used for temporary storage of data and program instructions. Programs and data are placed on it when they are executed or handled. The data stored in RAM can be changed as well as being read. To store data permanently we have to send it to secondary memory like disks because if the power of a Computer is shut OFF, everything stored in RAM will be lost. RAM is expensive, having less storage capacity but it performs operations with very high speed.
RAM is of two types:
1) Core RAM
2)
Semiconductor RAM
1) Core RAM
It is an older type of RAM. It had the advantage of being nonvolatile; even though we shut OFF the power, a core RAM continues to store data. The disadvantage of core RAM is that they are very expensive and it is harder to work with them as compared to semiconductor RAM.
2) Semiconductor RAM
Semiconductor RAM is of two types:
a) SRAM
b) DRAM
a) SRAM (Static RAM)
It is much cheaper than core RAM. Data is stored in SRAM unto the continuation of power supply. It is easier to use SRAM.
b) DRAM (Dynamic RAM)
It is cheaper than SRAM. It is highly volatile because not only must the power be kept on, but the capacitor charge must also be refreshed every 2-4 milli seconds (this refreshing is done automatically).
Expansion Slots (buses)
It is the collection of electronic connections that rotates together on motherboard. Because of expansion slots on motherboard we are able to add different devices and cards to our Computer for extra functionality.
Adapters (Cards)
Adapters are those elements, which are connected to motherboard with the help of expansion slots (buses). Some adapters support other devices and some are used to add extra functionality to the Computer. Many motherboards come with built-in-adapters and we are unable to exchange them.
Disk Drives
It is a device, which is used to store the data on disk and to provide the saved data from disk.
CD ROM
Disk
Disk is a mass-storage magnetic medium. We use disks because it stores our data permanently. We can also recall the saved data from disk for further work.
Types of Disks
Commonly used disks are of three types.
1) Floppy Disks
2) Hard Disks
3) Compact Disks (CDs)
1) Floppy Disks
Floppy disks are somewhat flexible disks. Generally floppy disks are available in 5.25” and 3.5” sizes.
Floppy disks are used to transfer small amount of data (files) from one Computer to another.
5.25” Floppy
2) Hard Disks
Hard disks are fixed disk drives. These are fixed in system unit of Micro-Computers. Hard disks are used due to their large capacity, easy-in-use nature and unmovable characteristics. Now-a-days hard disks are available in 2 GB, 4 GB, 8 GB, 10 GB, 15 GB 20 GB etc. capacities.
Hard Disk
3) Compact Disks (CDs)
Compact disks are gaining more popularity than floppy and hard disks, due to their less price and large capacity.
Generally CDs are used for installation, watching movies, listening music, for playing games etc.
CDR (Compact Disk Recorder)
It is a device with the help of which we can store data in CD.
Cables
Normally all types of devices attached to Computer have two types of cables.
1) Power Cable
2) Data Cable
1) Power Cable
It supplies power to the device.
2) Data Cable
With the help of data cable, data is transferred from one place to another.
HDD / CD
ROM Cable
Power Supply
Power supply supplies exact amount of power to motherboard and other devices inside system unit. It also converts AC (alternating current) to DC (direct current).
Ports
Places where data cables of external devices are connected
to system unit are called ports. Every device has special port.
Due to data transferring, ports can be divided two types:
1) Serial Communication Port
2) Parallel Communication Port
1) Serial Communication Port
Data is transferred bit by bit from serial communication port i.e. one bit at a time.
2) Parallel Communication Port
Data is transferred byte by byte from parallel communication port i.e. one byte at a time.
Keyboard
It is an input device, which is just like a typewriter’s
keyboard. However it contains some special keys. Keyboard can be used to communicate
with Computer.
Keys of keyboard can be divided into various groups:
Alphabetic Keys (A-Z)
These keys are used to enter alphabetic data. They are located in the center of the Keyboard consisting of 3 rows.
Numeric Keys (0-9)
These keys are used to enter numeric data; we can also use them for calculating. These keys are located on the top of alphabetic keys.
Numeric Pad
Numeric pad consists of numeric and arrow keys. These keys can be used for both purposes i.e. for calculating and for playing games etc.
Function Pad (F1, F2, F3.... F12)
It is consisted of 12 keys. These are assigned as F1, F2, F3 etc. Function of each key varies from Software to Software.
Special Keys (Enter, Shift, Esc etc.)
These keys are used for special or single function in every program.
Arrow Keys (up, down, right and left arrow keys)
Arrow keys are used to move cursor. Mostly they are used for playing games.
Mouse
The mouse is an input device. It is a pointing device, which rolls on a small bearing and has one or more buttons on the top. When a user rolls the mouse across a flat surface, such as a desk, the screen cursor moves in the direction of the mouse’s movement. This movement positions the cursor on a menu choice that the user has selected. With a click of the mouse’s button, the system can be notified of this choice. Positioning a cursor with a mouse is easier for non-typists than pressing various keys combinations. With proper Software, a mouse can also be used to draw pictures on the screen and edit test.
Printer
A device that is capable to give reports and all other types of data/information in written form is called printer.
Dot-Matrix Printer Ribbons
HP Laser Printer
Plotters
Plotters are widely used for drawing and map printing purposes.
Introduction
Every element of Computer attached to Computer with special cables or any part of Computer is known as device. Some devices are very important to our Computer and some are added for extra functionality. Some are used to enter data and some are used to provide output. Devices enable us to communicate with Computer.
Device Driver
Every device attached to Computer has a special program, which enable the operating system how to handle the device. This program is known-as device driver.
Our Interface With Computer
Data is created in many places and in many ways. Before data can be processed and stored, that must be translated to a form that Computer can understand. For this, we need input devices.
Once the data has been processed, that must be translated back to the form that we can understand. For this, we need output devices.
Input Devices / Unit
Devices used to enter data to Computer are called input devices. The user to communicate with Computer uses an Input device. When we enter any source of data to Computer with the help of any input device, the input unit of that device converts the data to machine language for further operation.
Following are some input devices:
Keyboard
Already discussed.
Light Pen
It looks like a fountain pen with a light sensitive cell at its tip, when this tip is placed near the screen, the Computer system can determine its position. It is normally used in graphic applications to draw lines and maps on the screen. Some types of light pens are used to “point” the certain areas of screen as per user requirement.
Scanner
It is a camera fitted device, which picks images from our written/printed documents and transfers them to the Computer so that these could be used where needed.
Floppy / Hard / Compact Disks
Already discussed.
Audio / Video / Blaster card
Such a type of card is used to save songs/video films etc. into Computer or play them from Computer. It can be used in a number of relevant tasks.
Fax / Modem Card
Such types of cards are used to receive or transfer messages/ files/ documents etc. (prepared in Computer) from one Computer to another via telephone line.
Magnetic Tapes
Just like Audiotapes these tapes are used as input device. In older Micro-Computers, Magnetic-Tapes are shaped as audio tapes, but in Mini and Main Frame Computer, it comes in a larger shape. Normally their Reel is 2400 feet long and ½ inch wide. It stores data at the rate of 6240 bytes per inch.
Mark Reader
It is a device that automatically senses the marking on paper documents and sends the information to Computer or like wise. It is commonly used for the checking of objective type papers etc.
Magnetic Ink Character Reader
This device senses the characters written by magnetic ink. Such a type of technology is used in banks to check the Bank Code, Account Number and the Cheque Number etc.
Optical Character Reader
This device is used to read the optical stylized characters written with special reference either by hand or by Computer.
Bar Code Reader
Bar codes are actually straight line representing their corresponding digits from left to right. You can see these codes on mostly imported items in Pakistan. Bar Code Reader is consisted upon the following:
1) A light source (LED) focussed on the code.
2) A photoelectric cell, which senses the presence or absence of reflected light from the Bar codes. As the bar codes are vertical lines, a combination of B&W strips. Black lines represent the existence of code whereas white strips represent their absence.
3) A circuit, which amplifies the signals, obtained from the codes.
4) Analogue to Digital converts, which converts the signal received from the codes to digits.
Voice Synthesizer
This device listens the user’s voice and while converting it into Digital form sends to the Computer.
Output Devices / Unit
Those devices that provide results for the user are called output devices. The Computer to communicate with us uses an output device. As you know that Computer perform all the operations in binary codes and the results produced is also in binary form. Therefore the output unit receives the results in binary form and converts it into human readable form before communication with the user.
Following are some output devices
Monitor, Printer, Plotter, Disks
Already discussed.
Audio / Video blaster card, Fax / Modem Card, Magnetic Tapes, CDs
All of them are used as input as well as output devices.
Micro Film
A Microfilm provides much more space of storage. Normally a 4x6-inch microfiche card can contain the data equal to 270 printed pages. It is useful for organizations that must keep massive files of information that don not need to be updated