1.5 Functional units of a computer

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FUNCTI ONAL UNI TS OF A COMPUTER

Para 1.5

1.5 FUNCTIONAL UNITS OF A COMPUTER

A co mputer syste mhas four basic functi onal units which are listed as under : (1) Input Unit (2) Output Unit (3) Me mory Unit (4) Control Unit (5) Arith metic Logic Unit The l ast t wo units i. e. Control Unit, Me mory Unit and Arit h meti c and Logi c unit toget her w it h i nternal processor constit ute , the brai n of a coCentral Processing mputer. Just Li ke a Unit (CPU) hu man brai n, it controls the fl ow of i nfor mati on andtells other co mponents what to do. The speed of the co mputer depends upon what type of CPUis used. A CPUgenerates l ots of heat; andtherefore, thereis usuall y a s mall fan nearbyto cool it down. The functi onal rel ati on a mong the vari ous co mponents of a co mputer can be shown sche maticall y as foll ows:

CENTRAL PROCESSING UNIT (CPU)

Input unit Arith metic & Logic unit

Control unit

Me mory unit Output unit

( Pri mary Me mory: RAM , ROM ) Secondary Me mory: Hard disk, CD ’ s, DVD ’ s, Pendri ves, etc.

FIGURE 1.5 : SCHEMATICALLY DIAGRAM OF CPU

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Para 1.5

BASI C COMPUTER CONCEPTS AND NET WORKI NG

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The Process W iththe use of i nput devices data or i nstructi ons are enteredi nto a co mputer. Thei nput devices li ke keyboard, mouse, etc. are co mmonl y usedtoi nput data and i nstructi ons. W ith the hel p of a keyboard al phanu meric characters and sy mbols are first convertedi nto machi nel anguage andthen sent to CPU . The mouse is used to pick or select a co mmand fro mthe monitor screen. The central processi ng unit co mprises a processor whichi nterpretsthe progra m i nstructi ons and manages the fl ow of data. The data is first sent to control unit which dependi ng uponthe need sends it to arith metic andl ogic unit or to me mory unit. If need be the arith metic andl ogical unit processes the data and converts it i ntoi nfor mati on. The progra mi nstructi ons are processed one at a ti me al ong w iththe necessary data. The results obtai ned fro mthe process are then sent to me mory unit and the next i nstructi on is processed. This process is repeated until the entire progra mis executed. The results so obtai ned are then sent to output units so that the users ( hu man bei ng) can understand and use the i nfor mati on so generated. All the units be it i nput unit, control unit, arith metic and l ogic unit, me mory unit or output unit, work i n coordi nati on so that the data processi ng re mai n s mooth and co mputi ng re mai ns user friendl y. The i ndi vi dual role of these units is expl ai ned bel ow:

Input Unit Thei nput unit uses the appropri ate methodto enter data or progra mi nstruc ti ons to the co mputer syste m . It converts the data i nto a suitable for mt -hat can be understood by the co mputer. Different types of data need different i nput methods ( devices). For exa mple for enteri ng bar code data a bar code reader is required.

Arithmetic and Logic Unit The arith metic-l ogic unit ( ALU) perfor ms arith metic andl ogical operati ons on the data. This secti on of the machi ne can be rel ati vel y s mall consisti ng of cir cuits andregisters which perfor marith metic( + , -

, × , /) andl ogical ( > , < , <= , >= , etc.) operati ons. The Arith metic-l ogic unit which can perfor m mathe matical or l ogical operati ons for ms the backbone of the co mputers. After co mpleti ng the required process it ret urns the output to control unit.

Control Unit The control unit controls and coordi nates the overall functi oni ng of the co m puter syste m . It is the manager of the co mponents of the co mputer. It se nds co mmand si gnals and controls the sequence of i nstructi ons to be executed. It is responsi ble not onl y for managi ng the sequence of the i nstructi ons to be perfor med but also the retrieval of i nstructi ons i n the proper sequence.

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FUNCTI ONAL UNI TS OF A COMPUTER

Para 1.5

The functi on of the control circuitryi n a general purpose co mputer is toi nter pret thei nstructi ons andthensequence the necessary si gnals tothose secti o ns of the co mputer which w ill perfor mthe i nstructi ons.

Memory Unit: The me mory unit stores all the i nput data and the results. Me mory Unit of a co mputer can be di vi dedi nto t wo: pri mary me mory and secondary me mory. The pri mary me mory of a co mputer or mai n me moryis called

Random Access Memory (RAM),

and

Read Only Memory (ROM).

RAMis a se m i-conductor chi p. It is a vol atile me mory, as l ong as power is on the i nfor mati on storedi n it re mai ns. Once the power is l ost, thei nfor mati on storedi nthe RAMalso gets erased. ROM contai ns i nstructi ons for the m icroco mputers. It further may be di vi ded i nto t wo: , one ti me progra mmable non- Programmable Read Only Memory (PROM)vol atile me mory chi ps that are manufact ured bl ank and dependi ng upon the technol ogy can be progra mmed at wafer, fi nal test or i n syste m , and , atype of me mory c Erasable Programmable Read Only Memory (EPROM)hi p that retai ns its data when the power suppl y is s w itched off. The progra mmes stored on EPROM can be erased by exposi ng it to very strong ultravi olet li ght source. The contents of ROMare deter m i ned at theti me of manufact uri ng of the chi ps. ROMis not a vol atile me mory. Thei nfor mati on stored doesn ’t get erased even if the power is l ost. The most i mportant ROMchi p is the

Basic Input/Output System or BIOS

. The BI OS is a collecti on of s mall co mputer progra ms built i nto a ROMchi p. The secondary me mory is i n the for m of a hard disk which is a non-vol atile me mory generall y measuredi n Gi gabytes ( GB), the other secondary me mory devices are pen dri ves, CD ’ s, DVD ’ s, etc. These are used to store data per ma nentl y. These are also called backup me mory and are used to keep the data for a very l ong peri od of ti me.

Output unit:

The output unit convertsthei nfor mati on generated by co mputers i n machi ne l anguage to the for mi n which the user can understand. A variety of output devices are used for different purposes li ke monitors to displ ay the i nfor mati on, pri nters to pri nt the output, speakers to provi de audi o output, etc.

Role of Registers and Cache , a speci al purpose me mory is i nstru mental i n movi ng data to and Register fro m the mai n me mory while the data processi ng is executed. To execute an i nstructi on the CPU uses these registers for hol di ng data for processi ng. Registers, though a part of CPU , do not for m part of mai n me mory. Onl y a piece of data can be hel d by the registers at a ti me. While the i nstructi ons are under executi on the relevant data are recei ved by the registers, hel d by the registers te mporaril y and then the data is passed on by the registers as per the i nstructi ons fro mthe control unit. For executi ng the next i nstructi on the

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