Chap1.1 Computer Introduction

8/12/2019 Chap1.1 Computer Introduction

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UNIT 1 : COMPUTER SYSTEM ORGNIZATION

WHAT IS A COMPUTER?

The word computer comes from the word compute which means to calculate. So acomputer is normally considered to be calculating device that can perform arithmeticOperations at enormous speed.

CHARACTERSITICS OF COMPUTERS

The power and usefulness of computer is due to the following characterstitics:

1. ATO!AT"#: Once a $ob is started it will wor% by itself without human

intervention until the $ob is finished.

&. S'((): A computer is a very fast device. "t can perform in a few seconds theAmount of wor% that a human being cn do in an entire year.

!icroseconds *1+(,- anoseconds *1+(/-

'icoseconds*1+(1&-

0. A##A#2 : The accuracy of a computer is consistently high and the degree of

Accuracy of a particular computer depends upon its design.

#O(#T "'T"ST#T"O (3"A43(5A##AT( OT'T

#omputer error caused due to incorrect input data or unreliable programs is called

6arbage in 6arbage out *6"6O-

7. )(3"6(#( : A computer is free from monotony8 tiredness8lac% of

concentration8 and can wor% for hours together without creating any error and

without grumbling.

9. (SAT"3"T2: #omputer can do many things together or simultaneously. "t can

prepare result8 prepare electricity bill8 type a important letter together.

,. 'O;( O< (!(!4("6: A computer can store and recall any amount ofinformation because of its secondary storage. (ven after several years 8 theinformation recalled would be as accurate as day one.

=. O ".> ? A computer is not a magical device."t possesses no intelligence of itsown. "t has to be told what to do and in what se@uence. A computer cannot ta%es

its own decision.


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Output unit supplies the information obtained as a result of data processing to the outside

world. Thus it lin%s the computer with the eHternal world.

The following functions are performed by the output unit:

"t accepts the results produced by the computer8 which are in the coded form andhence cannot be easily understood by us.

"t converts these coded results to human acceptable form

"t supplies the converted results to the outside world.

STOA6( "T

The data and instructions that are entered into the computer system through input

devices have to be stored inside the computer before the actual processing starts.

Also8 the result produced by the computer after processing must be also %eptsomewhere inside the computer before being passed on to the output units.

Also 8 the intermediate results need to be stored.

The specific function of the storage unit are

All data to be processed and the instruction re@uired for processing

"ntermediate results of processing


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A"TI!(T"# 3O6"# "T

"t is the place where actual eHecution of the instruction ta%es place during the

processing operation.

All calculations 8 comparisons and decisions are made in the A3.

o processing in done in the primary memory8 intermediate results are calculatedand send bac% to primary memory.

#OTO3 "T

"t maintains order and direct the operations of the entire system.

"t does not perform any actual processing of data 8 the control unit acts as a central

nervous system for other components of the computer system.

"t manages and coordinates the entire computer system.

#(TA3 'O#(SS"6 "T*#'-

The control unit and A3 together are %now as #'.

All ma$or calculations and comparsions are made inside the #'

#' is also responsible for activating and controlling the operations of other

units of the computer system.

;IAT "S A #O!'T( S2ST(!J ;I2 "S "T #A33() S2ST(!J

A system is a group of intergrated parts have a common purpose of achieving someob$ective. Three main characteristics are %ey to a system

1. A system has more than one element

&. All elements are logically related.0. All the elements of a system are controlled in such a way that the goal is

achieved.

Since #O!'T( is made up of input8 output8storage and #' that wor% together

to perform the steps called for in the program being eHecuted 8 it is called a computer

system.

(ach part separately is useless ony when put together they form a system.

The two basic types of computers are

1. AA3O6

&. )"6"TA3


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AA3O6 computer handles or process information which is of physical nature eHample

temperature8 pressure etc.

)"6"TA3 computer process information which is essentially in binary or two state form

namely Cero or one. )igital computer fall into ranges called microcomputer8

minicomputers8 mainframes and supercomputers8 classified in ascending order of siCe ?small medium8large and very large.

BINARY NUMBER SYSTEM

The binary number system is eHactly li%e the decimal number system eHcept tha the

base is & instead of 1+. There are only two symbols * + and 1-

!ethod of converting binary to decimal

The decimal e@uivalent is obtained by multiplying each binary digit with its positionalvalue. The right most bit has positional value &e+8 second right most bit has &e1 and so

on.

#onvert decimal to binary

)ibble dabble method)ecimal number to be converted is repeatedly divided by &. The remainder +s and 1s so

obtained are read in reverse order in order to obtain the binary e@uivalent of the decimalnumber. The number is divided till the @uotient is +.

(K(#"S(:


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1. &79

&. 790. 07

7. &1

9. ,9,. =

=. &+1

. 1&/. /+

1+. =

AS#"" *American Standard #ode for "nformation "nterchange- is used to represent data

internally in microcomputer.

AS#"" are of two types

1. AS#""5= is a =5bit code that allow 1& different characters. The first 0 bits areCone bit and last 7 bits indicate the digits.

&. AS#""5 allows &9, different characters. The first 7 bits are Cone bit and last 7

bits indicate the digits.

LLLLLLLLLLLLLLLLLLLLLLLLLLLLLL() LLLLLLLLLLLLLLLLLLLLLLLLLL

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Chap1.1 Computer Introduction