Mathematics Department 1

Chapter 3Chapter 3Computer Hard wareComputer Hard ware

A computer performs basically five major operations :

1. it accepts data or instructions by any way of input,

2. it stores data, 3. it can process data as required by the user, 4. it gives results in the form of output, and 5. it controls all operations inside a computer

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• Refers to the physical components• Not one device but a system of many

devices• Major types of components include:

– Central Processing Unit– Main memory– Secondary storage devices– Input devices– Output devices

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CentralProcessing

Unit

MainMemory

InputDevice

OutputDevice

SecondaryStorage

• Fetches instructions from main memory• Carries out the operations commanded by

the instructions• Each instruction produces some outcome• A program is an entire sequence of

instructions• Instructions are stored as binary numbers• Binary number - a sequence of 1’s and 0’s

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Commonly known as random access memory, or just RAM

Holds instructions and data needed for programs that are currently running

RAM is usually a volatile type of memory

Contents of RAM are lost when power is turned off

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A nonvolatile storage medium Contents retained while power is off Hard disk drives are most common

› Records data magnetically on a circular disk› Provides fast access to large amounts of data

Optical devices store data on CD’s as pits USB flash memory devices

› High capacity device plugs into USB port› Portable, reliable, and fits easily in a pocket

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Any type of device that provides data to a computer from the outside world

For example:› Keyboard› Mouse› Scanner

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• Any type of device that provides data from a computer to the outside world

• Examples of output data:– A printed report– An image such as a picture– A sound

• Common output devices include:– Monitor (display screen)– Printer

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Two typical components of a CPU are: The arithmetic logic unit (ALU), which performs

arithmetic and logical operations. The control unit (CU), which extracts

instructions from memory and decodes and executes them, calling on the ALU when necessary.

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The actual processing of the data and instruction are performed by Arithmetic Logical Unit

The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison.

Data is transferred to ALU from storage unit when required

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The Control Unit acts like the supervisor It extracts instructions from memory and decodes and

executes them, and sends the necessary signals to the ALU to perform the operation needed.

The control unit determines the sequence in which computer programs and instructions are executed.

Processing of programs stored in the main memory, interpretation of the instructions and issuing of signals for other units of the computer to execute them.

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There are two kinds of computer memory: primary and secondary.

Primary memory is accessible directly by the processing unit.

RAM (Random access memory) is an example of primary memory

As soon as the computer is switched off the contents of RAM is lost.

You can store and retrieve data much faster with primary memory compared to secondary memory

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Secondary memory such as floppy disks ,hard magnetic disk, etc., is located inside and outside the computer.

Primary memory is more expensive than secondary memory.

The size of primary memory is less than that of secondary memory.

Primary memory is faster than secondary memory.

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There is another memory in computer, which is called Read Only Memory (ROM).

The storage of program and data in the ROM is permanent.

The ROM stores some standard processing programs supplied by the manufacturers to operate the computer.

The ROM can only be read by the CPU but it cannot be changed.

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PROM is another type of primary memory in computer, which is called Programmable Read Only Memory (PROM).

You know that it is not possible to modify or erase programs stored in ROM, but it is possible for you to store your program in PROM chip. Once the programmes are written it cannot be changed and remain intact even if power is switched off.

Programs or instructions written in PROM or ROM cannot be erased or changed.

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EPROM: Erasable Programmable Read Only Memory, which over come the problem of PROM & ROM.

EPROM chip can be programmed time and again by erasing the information stored earlier in it.

When the EPROM is in use information can only be read.

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