Computer Fundamentals notes of mca 1st sem

computerr fundamnetal

1. Unit –I
Introduction to Computers
•WhatisComputer?
–Theword‘computer’comesfromtheword‘compute’,
whichmeans‘tocalculate’.
•Hence,peopleusuallyconsideracomputertobeacalculating
devicethatcanperformarithmeticoperationsathighspeed.
•Infact,theoriginalobjectiveforinventingacomputerwasto
createafastcalculatingmachine.However,morethan80%of
workdonebytoday’scomputerisofnon-mathematicalornon-
numericalnature.
•Moreaccurately,wecandefineacomputeras–Adevicethat
operatesupondatalikebio-data,marksobtained,employee
personaldetails,songs,videoetc.
•Hence,datacomesinvariousshapes&sizesdependingupon
thetypeofcomputerapplications.

2. •Somecommondefinitionsofcomputer–
–Calculatingdevicethatcanperformarithmeticoperationat
anenormousspeed.
–Anelectronicdevicewhichiscapableofcreatingsolutionby
performingcomplexprocessingatinformation.
–Anelectronicdeviceforthestorage&processingof
information.
–Anelectronicdevicethatstores,retrieveandprocessesdata
andcanbeprogrammedwithinstructions.
–Amachinethatacceptsdataandmanipulatesitforsome
resultbasedonaprogramwhichdescribeshowdataistobe
manipulatedorprocessed.
–Amulti-functionelectronicdevicethatcanexecute
instructionstoperformatask.
–Amachinethatacceptsinput,processesitaccordingto
specifiedrulesandproducesoutputaccordingly.
–Anelectronicdevicewhichprocessesdataunderthecontrol
ofasetofinstructionscalledprogramtoproducedesired
result.

3. What is Data, Information and
Data Processing?
•Data–
–Itisthepluralformof‘datum’meaning‘fact’.
–Itcanbedefinedasrepresentationoffactsorobservations.Foreg.Number,
words,quantities,amountetc.aredata.
–Dataarerepresentedbysymbols.
•Information–
–Dataarrangedinusefulandmeaningfulformisknownasinformation.Insimple
wordswecansaythatDataarerawmaterialwhileinformationismeaningfully
orderedorstructureddataproducedasoutputofdataprocessing.
–Ithasalwaysacontextwhereasthedatamaybecontextfree.
•DataProcessing–
–Theactivityofprocessingdatausingacomputeriscalleddataprocessing.
–Dataprocessingconsistsofthreesub-activities–
•Capturinginputdata
•Manipulatingthedata
•Managingoutputresults.
–Hence,dataisrawmaterialusedasinputtodataprocessingandinformationis
processeddataobtainedasoutputfromdataprocessing.

4. •Data–
–Fact,observation,assumptionoroccurrenceofanevent.
–Providesknowledgeorinformationorvaluetoanindividual
orbusiness.
–Compiledtoformreports,figures,documentsetc.
–Rawmaterialforinformation
–Maybealphabetic,numericorspecialsymbol.
•Information–
–Organizedorclassifieddata
–Finishedproduct
–Musthavesurprisingvaluetotheuser.
•DataProcessing–
–Reconstruction,manipulatingorre-orderingofdataby
people/machinetoincreaseitsusefulnessandvaluefor
someparticularpurpose.

5. Characteristics of Computer
•Automation–Computersareautomaticmachinesbecauseoncestartedonajob,they
carryoutthejob(normallywithouthumanassistance)untilitisfinished.
•Speed–Acomputerisaveryfastcalculatingdevice.Itcanperformbillionsofinstructions
inafractionofsecondandthattoowithoutanyerror.
•Accuracy–Inadditiontobeingfast,computersareveryaccurate.Acomputerperforms
everycalculationwiththesameaccuracy.However,errorscanoccurinacomputer.These
errorsaremainlyduetohumanratherthantechnologicalweaknesses.
•Diligence–Unlikehumanbeings,acomputerisfreefrommonotony,tirednessandlackof
concentration.Itcancontinuouslywordforhourswithoutcreatinganyerrorandwithout
grumblingi.e.ifmillionsofcalculationsaretobeperformed,acomputerwillperformthe
lastonewithexactlythesameaccuracyandspeedasthefirstone.
•Versatile–Acomputerisahighlyversatilemachineasitcanperformno.oftasksatthe
samemoment.Onemomentitispreparingresultsofanexamination,anothermoment
preparingelectricitybillandverynextmomentplayinggameetc.
•Large&PerfectMemory–Asahumanbeingacquiresnewknowledge,his/herbrain
subconsciouslyselectswhatitfeelstobeimportantandworthretaininginmemory.The
brainrelegatesunimportantdetailstobackofmindorjustforgetsthem.Thisisnotthe
casewithcomputers/Acomputercanstoreandrecallanyamountofinformationbecause
ofitslargestoragecapacity.Itcanretainapieceofinformationaslongasauserdesires
andtheusercanrecalltheinformationwheneverrequired.

6. Limitations of Computers
•NoI.Q.(intelligencequotient)–Acomputerisnota
magicaldevice.Itpossessesnointelligenceofitsown.
ItsI.Q.iszero.Ithastobetoldwhattodoandinwhat
sequence.Acomputercannottakeitsowndecisions.
•NoFeeling–Computersaredevoidofemotions.They
havenofeelingsandnoinstinctsbecausetheyare
machines.Basedonoutfeelings,taste,knowledgeand
experienceweoftenmakecertainjudgmentsinour
day-to-daylifewhereas,computerscannotmakesuch
judgmentsontheirown.Theymakejudgmentsbased
ontheinstructionsgiventothemintheformof
programsthatarewrittenbyus.

7. Evolution of Computer
Necessity is the mother of evolution…
2400B.C.Abacus–earliestcalculatingdevice
1600 NapierBonesbyJohnNapier–usedformultiplicationanddivision
1620 SlideRule-multiplicationanddivision
1642 PascalineorPascalineCalculatorbyBlaisePascal–foradditiononly
1671 LeibnizCalculatorbyGottfriedVonLeibniz–firstcalculatorformultiplication,also
describethebinarynumeralsystem
1801 JosephMarieJacquard–weavingpatternusingPunchedCards
1822 DifferenceEnginebyCharlesBabbageforcomputingtable
1833 AnalyticalEnginebyCharlesBabbage(fatherofmoderndigitalcomputer)–base
ofmoderndigitalcomputer,usedpunchedcardsforinput,steamenginefor
power,generalpurposeprogrammablecomputer
1843 LadyAdaLovelace–firstprogrammer
1847 GeorgeBoolepublishedthepaperforBooleanAlgebra–thebasicofmodern
computationtheory
1880 HermanHollerithdevelopedHollerithTabulatingMachine(thecoreofIBM)uses
punchedcards

8. 1937 ClaudeShennonimplementedBooleanAlgebrausingelectronicrelays&switches
1939 HowardMark-IorAutomaticSequenceControllerCalculator(ASCC)byHoward
A.AikenincollaborationwithIBM–firstelectromechanicalcomputer
1943-46ENIACbyProf.J.PresperEckert&JohnMouchly-firstallelectroniccomputer
1946–52EDVAC–amajordrawbackofENIACwasthatitsprogramwerewiredonboards
thatmakeitdifficulttochangetheprograms.
Dr.JohnVonNeumannintroducedthe‘storedprogram’conceptasaresult
sequenceofdataandinstructionscanbestoredinthememoryofacomputer.
Duetothisfeature,weoftenrefertomoderndigitalcomputersas‘stored
programdigitalcomputer’.
1947–49EDSAC(Electronicdelayedstorageautomaticcalculator)byProf.MauriceWilkes
1951 UNIVAC-1(UniversalAutomaticComputer)–firstdigitalcomputer
1955 IBMintroducesfirsttransistorbasecalculator
1957 FORTRAN–firstHLLforscientificapplication
1971 Intelfirstmicroprocessor–4004

9. Functional Components of a Computer
•Acomputerfollowsinput-process-output(IPO)
cycle.
•Thefirststageisperformedincomputerbyinput
unit.
•Thesecondstageisperformedbythecentral
processingunit.
•Thethirdstageisperformedbyoutputunit.
•Themainmemoryholdstheinputand
intermediateoutputduringtheprocessing

10. •The basic structure of a computer is as shown
below -
Input Unit Output Unit
Central
Processing
Unit
Main Memory
Storage Device

11. Input Unit
•Theinputunitisresponsiblefortakinginputand
convertingitintocomputerunderstandableform
(binarycode).
•Theinputunitisformedbytheinputdevicesattached
tothecomputer.
•Examplesofinputmediaare:keyboard,mouse,
magneticinkcharacterreader(MICR),opticalcharacter
reader(OCR),opticalmarkreader(OMR),joysticketc.
•Inputcomprisedofdata&instruction.
S.No.Input Data Instruction
1 Purchase Cake & Pastries Cake, Pastries Purchase
2 Make a phone call at 74551657455165 Make a phone call
3 Make tea using ingredients Ingredients Make tea

12. Central Processing Unit (CPU)
•TheCPUisthecontrolcentreforacomputer.
•Itguides,directsandgovernsitsperformance.
•Itisthebrainofthecomputer.
•TheCPUhastwocomponentswhichare
responsiblefordifferentfunctions.
•Thesetwocomponentsare–
–ControlUnit(CU)and
–ArithmeticLogicUnit(ALU).

13. ALU
•TheALUperformsallthefourarithmetical(+,-,*,/)
andsomelogical(<,>,=,<=,>=,<>)operations.
•Whentwonumbersarerequiredtobeadded,these
numbersaresentfrommemorytoALUwhereaddition
takesplaceandtheresultisputbackinthememory.In
thesamewayotherarithmeticoperationsare
performed.
•Forlogicaloperationalso,thenumberstobecompared
aresentfrommemorytoALUwherethecomparison
takesplaceandtheresultisreturnedtothememory.
•TheresultofalogicaloperationiseitherTRUEor
FALSE.
•Theoperationsprovidethecapabilityofdecision-
makingtothecomputer.

14. Control Unit (CU)
•TheCUcontrolsandguidestheinterpretation,flowand
manipulationofalldataandinformation.
•TheCUsendscontrolsignalsuntiltherequiredoperationsare
doneproperlybyALUandmemory.
•AnotherimportantfunctionofCUistheprogramexecution
i.e.carryingoutalltheinstructionsstoredintheprogram.
•TheCUgetsprograminstructionsfrommemoryandexecutes
themoneaftertheother.
•AftergettingtheinstructionsfrommemoryinCU,the
instructionisdecodedandinterpretedi.e.whichoperationis
tobeperformed.
•TheCUevencontrolstheflowofdatafrominputdevicesto
memoryandfrommemorytooutputdevices.

15. Output Unit
•Theoutputunitisformedbytheoutputdevices
attachedtothecomputer.
•TheoutputcomingfromtheCPUisintheformof
electronicbinarysignalswhichneedsconversionin
someformwhichcanbeeasilyunderstoodby
humanbeingsi.e.characters,graphicaloraudio
visual.Thisfunctionofconversionisperformedby
outputunit.
•SomepopularoutputdevicesareVDU(visual
displayunit),printer,plotter,speechsynthesizerand
codeetc.

16. The Memory
•Thememoryofacomputerisoftencalledmainmemoryorprimary
memory.
•ItisgenerallythethirdcomponentofCPU.
•Itismorelikeapredefinedworkingplace,whereittemporarilykeeps
informationanddatatofacilitateitsperformance.
•Thememoryofacomputercanbethoughofas‘cell’.
–Amemorycellmaybedefinedasadevicewhichcanstoreasymbolselected
fromasetofsymbols.
–Eachofthesecellsisfurtherbrokendownintosmallerpartsknownas‘bits’.
•Abitisanelementaryunitofmemory.
•Abitmeansabinarydigiti.e.either0or1.
•Anumberofbitstogetherareusedtostoredatainstructionsbytheircombination.
•Agroupof4bitsiscalleda‘nibble’andagroupof8bitsiscalled‘byte’.
•Onebyteisthesmallestunitwhichcanrepresentadataitemoracharacter.Otherunits
are–KB,MB,GB,TBetc.
•Sincecomputer’smainmemory(primarymemory)istemporary,secondary
memoryspaceisneededtostoredataandinformationpermanentlyfor
lateruse.Somemostcommonsecondarystoragemediaarethefloppy
diskette,harddisk,CD-RWetc.Thesecondarymemorydevicesarealso
knownasstoragedevices.

17. Major components of a computer system
•TheHardware
•TheOperatingSystem
•TheApplicationprogramroutines
–compilers,linkers,databasemanagementsystems,utility
programsetc.
•TheHumanware(users)
–Where,hardwareprovidesthebasiccomputingresources,
theapplicationprogramroutinedefinethewaysinwhich
theseresourcesareusedtosolvethecomputingproblemsof
theusersandtheOperatingSystemcontrolsandcoordinates
theuseofthehardwareamongthevariousapplication
programsforthevarioususers.Theoperatingsystemfrees
theapplicationsoftwaretoconcentrateonproducing
information.

18. User
Application Software
Operating System
CPU & Hardware
Interacts with
Interacts with
Interacts with
CPU

19. Hardware
•Hardwarerepresentsthephysicalandtangiblecomponentsofthe
computeri.e.thecomponentsthatcanbeseenandtouched.
•Theelectronic,electricalandmechanicalequipmentthatmakes
upacomputeriscalledhardware.
•Inputdevices,outputdevices,CPU,floppydisk,harddisketc.are
examplesofhardware.
•Peripherals
–Peripheralsarethedevicesthatsurroundthesystemunite.g.the
keyboard,mouse,speakers,printers,monitorsetc.
•Acomputerconsistsoffiveprimaryhardwarecomponents–
–Inputdevices,
–memory,
–CPU,
–outputdevices,
–storagedevices
•Thecomponentsworktogetherwithsoftwaretoperform
calculations,organizedataandcommunicatewithother
computers.

20. Software
•Softwarerepresentsthesetofprogramsthatgoverntheoperationof
acomputersystemandmakethehardwarerun.
•Theyarebroadlyclassifiedintothreecategories–
–OperatingSystem
–LanguageProcessor
–ApplicationSoftware
•OperatingSystem
–Anoperatingsystemisaprogramwhichactsasaninterfacebetweenauser
andthehardware(i.e.allcomputerresources).
–Anoperatingsystemisanimportantcomponentofacomputersystemwhich
controlsallothercomponentsofthecomputersystem.
–Operatingsystemisjustlikeoursecretary–wepassourorder/requeststo
operatingsystemand‘theoperatingsystem’doesitforus.‘OperatingSystem’
itselfdecides:Howtodo?;Whattodo?;Whentodo?
–Theprimarygoalofanoperatingsystemisthustomakethecomputersystem
convenienttouseandsecondarygoalistousecomputerhardwareinan
efficientmanner.

21. •Theoperatingsystemperformsthefollowingfunctions–
–Providestheinstructionstoprepareuser-interfacei.e.wayto
interactwithuserwhetherthroughtypedcommandsorthrough
graphicalsymbols.
–Loadsnecessaryprograms(intothecomputermemory)whichare
requiredforpropercomputerfunctioning.
–CoordinateshowprogramsworkwiththeCPU,keyboard,mouse,
printerandotherhardwareaswellaswithothersoftware.
–Managesthewayinformationisstoredonandretrievedfrom
disks.
•TherearevarioustypesofO.S.–
–Singleuser,multiuser,batchprocessing,multiprocessingetc.
–Asthenamesuggest,singleuserOSsupportssingleuserwhereas
multiusersupportsmultipleusers.ThebatchprocessingOS
processesthebatches(groups)ofjobsandmultiprocessingOSis
capableofhandlingmultipleCPU’satthesametime.

22. Language Processor
•Assembler
–Thislanguageprocessorconvertstheprogramwritteninassemblylanguage
intomachinelanguage.
•Interpreter
–ThislanguageprocessorconvertsanHLLprogramintomachinelanguageby
convertingitlinebyline.
–Ifthereisanyerrorinanyline,itreportsitatthesametimeandprogram
executioncannotresumeuntiltheerrorisrectified.
–Interpretermustalwaysbepresentinthememoryeverytimetheprogramis
executedaseverytimetheprogramisrun,itisfirstinterpretedandthen
executed.
–Forerrordebugging,interpreterisverymuchusefulasitreportstheerror(s)at
thesametime.Butonceerrorsareremoved,unnecessaryusageofmemory
takesplaceasithastobepresentinthememoryalways.
•Compiler
–ItalsoconvertstheHLLprogramintomachinelanguagebuttheconversion
mannerisdifferent.
–ItconvertstheentireHLLprograminonego,andreportsalltheerrorsofthe
programalongwiththelinenumbers.
–Afteralltheerrorsareremoved,theprogramisrecompiled,andafterthatthe
compilerisnotneededinthememoryastheobjectprogramisavailable.

23. Application Software
•Anapplicationsoftwareisasetofprogramsnecessary
tocarryoutoperations.Foreg.Inventorycontrol,
financialaccounting,railwayreservationetc.
•Subdividedintotwocategories–
–CustomizedApplicationSoftware:Thistypeofsoftwareis
tailor-madesoftwareaccordingtoauser’srequirements.The
softwareisdevelopedtomeetalltherequirementsspecified
bytheuser.However,thiscannotbedirectlyinstalledatany
otheruser’sworkplaceastherequirementofthisusermay
differfromthefirstoneandthesoftwaremaynotfitinthe
requirementsofthenewuser.
–GeneralPurposeApplicationSoftware:Thistypeof
softwareisdevelopedkeepinginmindthegeneral
requirementsforcarryingoutaspecifictask.Manyuserscan
useitsimultaneouslyasitfulfillsthegeneralrequirements.

24. Types of Computers
Computers
Digital
Purpose Wise
Special
Purpose
General
Purpose
Size and
Performance
Wise
Embedded Micro
Programmable Laptop Workstation
Mini Mainframe Super
Analog Hybrid

25. •DigitalComputers
–Thedigitalcomputersworkupondiscontinuousdata.
–Theyconvertthedataintodigits(binarydigits0&1)andall
operationsarecarriedoutonthesedigitsatextremelyfast
rates.
–Digitalcomputerscanfurtherbeclassifiedas:
•Purpose-wiseDigitalComputes
–SpecialPurposeComputerisdesignedtoperformaspecifictask.The
instructions(programs)tocarryoutthetaskarepermanentlystoredinthe
machine.Forthespecifictasks,thistypeofcomputerworksefficientlybut
suchcomputersarenotversatile.
–GeneralPurposeComputeristheonethatcanworkondifferenttypesof
programsinputtoitandthusbeusedincountlessapplications.The
programsarenotpermanentlystoredbutareinputatthetimeof
execution.Thesecomputersareveryversatile.
•SizeandPerformancewiseDigitalComputers
–EmbeddedComputers:
»Thesecomputersareembeddedwithincircuitryofappliancessuchas
television,washingmachineetc.
»Thesecomputersaretypicallypre-programmedforaspecifictasksuch
astuningtoaparticulartelevisionfrequencyetc.

26. –Microcomputers:
»AmicrocomputerisacomputerwhoseCPUisamicroprocessor.
»Amicroprocessorisaprocessorwhoseallcomponentsareonasingle
integratedcircuit(IC)chip.
»Theyaredesignedforperformingbasicoperationslikeeducational,
training,smallbusinessapplications,playinggamesetc.
»Furtherclassifiedas:
•ProgrammableComputerorPDAs(personaldigitalassistants):
•Theyareusedasnotepads,schedulingsystems,address
booketc.
•Ifequippedwithacellularphone,theycanconnectto
worldwidecomputernetworkstoexchangeinformation
regardlessoflocation.
•Laptop(Notebook)ComputersandDesktopPersonalComputers
(PCs):
•Theyhavelargeamountofinternalmemory.
•Theyareequippedwithkeyboard,amouse,track-balletc.
•TheyusuallyhavesimilarhardwareandsoftwareasPCs,but
theyaremorecompactandhaveflat,lightweightLCDs
insteadofvideodisplaymonitors.
•Laptopcomputers(alsocalledNotebooks)canbecarriedout
inbriefcases.
•Laptopcomputersaresocalledastheycansitonalapand
Desktopcomputersaresocalledastheycansitonadesk.

27. –Minicomputers
»Alsocalledmid-rangeservers,aremorepowerfulcomputersthan
micro-computersintermsofprocessingpowerandcapabilities.
»Theyaremainlymultiusersystemswheremanyusers
simultaneouslyworkonthesystems.
»Theypossessgreaterstoragecapacityandlargermemoriesas
comparedtomicrocomputers.
»Theyarecapableofhandlingmoreinput-outputdevices.
»ExamplesarePDP-11,VAX,7500Magnumetc.
–MainframeComputers
»Theyaredesignedtohandlehugevolumeofdataandinformation.
»Thesecansupportmorethanhundredusersatthesametime.
»Theyareverylargeandexpensivecomputersandhavegreat
processingspeedandverylargestoragecapacityandmemoryas
comparedtomicrocomputers.
»Thesecomputersevenpossessandworkwithmorethanone
processoratthesametime.
»Theyaremultiuser,multiprocessorsystems.
»ExamplesICL39,CDC6600,VAX8842,IBM3090/600etc.

28. –SuperComputers
»Thesecomputersconsistsofseveralprocessorsrunningtogether
therebymakingthemimmenselyfasterandpowerful.
»Theyarecapableofhandlinghugeamountofcalculationsthatare
beyondhumancapabilities.
»Theycanperformbillionsofinstructionspersecond.
»Thesecomputerscostin15-20milliondollarsrange.
»Theyaremainlyusedinapplicationslikeweatherforecasting,
nuclearscienceresearch,metrologyetc.
»Examples:CRAYX-MP-14,CDC-205,ETAGF-10,PARAMetc.
»Thepowerofasupercomputerisusuallymeasuredintermsof
‘floatingpointoperationspersecond’or‘flops’.

29. •AnalogComputers
–Inanalogcomputers,continuousquantitiesareused.
–Computationsarecarriedoutwithphysicalquantities
suchasvoltage,length,current,temperatureetc.
–Analogcomputersoperatebymeasuringratherthanby
counting.
–Themainadvantageofanalogcomputersisthatall
calculationstakeplaceinparallelandhencetheseare
faster.
–Theyaremostusedinengineeringandscientific
applications.
–Examplethermometer,voltmeter,ammeteretc.

30. •HybridComputers
–Thesecomputersutilizesthebestfeaturesofboththe
digitalandanalogcomputers.
–Theyarebestusedinhospitalswhereanalogpartis
responsibleformeasurementofpatient’sheartbeat,
bloodpressure,temperatureandothervitalsignsand
thentheoperationiscarriedoutindigitalfashionto
monitorpatient’svitalsigns.
–Hybridcomputersarealsousedinweatherforecasting,
submarinesetc.

31. Input Devices
•Aninputdeviceisanyhardwareusedtoenterdata,
programs,commandsanduserresponsesintoa
computer.
•Mostcommonare–
Keyboard,Mic,WebCamera,Mouse,Joystick,
Trackball,Scanner,MICR,OCR,OMR,BarCode
Readeretc.

32. Keyboard
•Animportantdataentrydeviceisthekeyboard
whichisatypewritelikedevice.
•Itcontainsamatrixofswitches(oneswitchperkey)
andakeyboardcontroller.
•Throughpressingandreleasingofswitches,
keyboardcontrollergeneratesascancodeusinga
firmwarelookuptable.ThisscancodeissenttoPC.
ThePChasanotherkeyboardcontrollerwhich
convertsthereceivedscancodeintoaspecific
character.

34. •Advantages
–Mostcommonandhistoricalwayofinputtingdata.
–Reliablewayofinputtingtextandnumbers.
–Availableinvarietyofformats.
•Disadvantages
–Notusefulforenteringsomespecifictypesofdata(eg.
pictures,diagram,voiceetc.)
–Veryslowwhileaccessingmenuoptionsorselecting
variousobjectsonscreen.
–Notmuchusefulforenteringorchangingsizesof
windowofscreen.
–Veryslowwhilemovingwindowsorotherobjects.

35. The Mouse
•Themouseisapointingdevicethatfitsunderpalmofa
hand.
•Mousecontrolsmovementofpointer(alsocalled
mousepointer)onscreen.
•Whenamousemovesonaflatsurface,thecursoron
thescreenalsomovesinthedirectionofmouse’s
movement.
•Amousegenerallyhastwoorthreebuttonsanditmay
ormaynothaveawheel.
•Withitsbuttonsandwheel,amousecanperformany
oneoftheseoperations:
–Point,Drag,DoubleClick,PressWheel,RotateWheel
–RightClick,Click,RightDrag

36. Types of Mouse
•MechanicalMouse:
–Amechanicalmousehasarubberormetalballonitsunderside.Whenthe
mouseismoved,itsballrolls.
–Mechanicalsensorswithinthemousedetectthedirectioninwhichtheballis
rollingandmovethescreenpointeraccordingly.
•Opto-mechanicalMouse:
–Thismouseissameasmechanicalmouseinthesensethatitalsohasaballon
itsundersideexceptitusesopticalsensorstosensethemotionoftheball.
•OpticalMouse:
–Thismousehasanopticalsensorinplaceofamouse-ball.
–Ituseslaserlighttodetectthemouse’smovement.
–Sincetheyhavenomechanicalmovingparts,theyrespondmorequicklyand
preciselythanmechanicalandopto-mechanicalmice,buttheyaremore
expansivecomparatively.
•WirelessMouse:
–Thesetypeofmousearenotphysicallyconnectedtocomputer.
–Theyuseseitherinfraredorradiowaves(eg.bluetooth)tocommunicatewith
computer.
–Theyaremoreexpensivecomparatively.

38. •Advantages
–Idealforpointingobjects/optionsondesktop
computers.
–Mostfamiliarandeasytousepointingdevice.
•Disadvantages
–Needaflatspaceclosetocomputer.
–Amousecan’teasilyusedwithalaptoporanotebook
orapalmtopcomputers
•Thesetypesofcomputers,insteaduseanothertypeof
pointingdevicesliketrackball,touchpad.

39. Light Pen
•Alightpenisalsoapointingdevice.
•Itconsistsofaphotocellmountedinapen-shaped
tube.
–Whenthepenisbroughtinfrontofapictureelementofthe
screen,itsenseslightcomingfromalimitedfieldofview.
–Thelightcomingfromthescreencausesthephotocellto
respondbygeneratingapulse.
–Thiselectricresponseistransmittedtoaprocessorthat
identifiesthepixel(graphicpoint)thelightpenispointingto.
–Clickingisperformedbypressingthepenonthescreen.
•Itprovidesnoinformationofthescreenwhenheld
overablankpartofthescreenbecauseitisapassive
devicewithasensoronly.
•Itisalsousedtodrawimagesonthescreen.

41. •Advantages
–Easytouse
–UsefulforprogramslikeCADforchangingshape,size,
location,colorsetc.ofthescreenimage.
–Candirectlydrawonscreen.
•Disadvantages
–Notveryaccuratewhiledrawing.
–Expensivecomparedtoalternatepointingdeviceslike
mouse.
–Tiresomeafterlongusagehours.

42. Touch Screen
•Atypeofdisplayscreenthathasatouch-sensitive
transparentpanelcoveringthescreenisknownas
touchscreen.
•Intouchscreen,agridoflightbeamsorfinewires
criss-crossthecompilerscreen.
–Whenyoutouchthescreenwithyourfinger,theraysare
blockedandthecomputersenseswhereyouhave
pressedandtherebyidentifiestheobjectwhichyou
wanttochoose.
•TheyareoftenusedinpublicplacessuchasBank
ATM,Airports,Travelagenciesetc.

44. •Advantages
–Easytouse
–NoextraperipheralsneededapartfromTouchScreen
monitorscreen.
–Noexperience/trainingrequiredtouseit.
•Disadvantages
–Notsuitableforinputtingbulkdata.
–Notveryaccuratewhilepointingtosmallareasofscreen
asfingerisrelativelylargeobject.
–Moreexpensivethanmouse.
–Tiresomewhenusedforlong.

45. Graphic Tablet
•Agraphictabletorsimplyatabletordigitizingtabletenables
toenterdrawingsandsketchesintoacomputer.
•Itconsistsofanelectronicsurfaceandacursororpen.
•Acursor(alsocalledapuck)issimilartoamouse,exceptthat
ithasawindowwithcrosshairsforpinpointplacementandit
canhaveasmanyas16buttons.
•Apen(alsocalledastylus)lookslikeasimpleballpointpen
butusesanelectronicheadinsteadofink.
•Thetabletcontainselectroniccircuitrythatenablesitto
detectmovementofthecursororpenandtranslatethe
movementintodigitalsignalsthatitsendstothecomputer.
•Aswedrawonthepad,theimageiscreatedonthescreen.
Thedrawingcreatedinthismannerareveryaccurate
(generallyuptohundredthofaninch).

47. •Advantages
–Veryusefulinenvironmentsinvolvingmoveofdrawings
etc.(eg.Fashiondesigning,artetc.)
–Effectivemethodforinputtingdrawingastheyare
drawn/created.
•Disadvantages
–Notveryusefulforpointingandclickingobjects.

48. Joystick
•Adevicethatletstheusermoveanobjectonthe
screen.
•Childrencanplaywithcomputersinasimplewayby
theuseofajoystick.Joystickmakesitmucheasier
forthemandprovidesabettercontrol.
•Itisasticksetintwocrossedgroovesandcanbe
movedleftorright,forwardorbackward.
•Themovementofthestickaresensedbya
potentiometer.
•Ajoystickisgenerallyusedtocontrolvelocityofthe
screencursorsmovementratherthanitsabsolute
position.

50. •Advantages
–Usefulforplayinggamesoncomputers.
–Givesimmediatefeelofdirectionduetomovementof
thestick.
•Disadvantages
–Involvesmorearmsandwristmovement,hencedifficult
tousebysomepeople.
–Notveryusefulforclicking/selectingobjects.

51. Microphone
•Wecansendsoundinput
tocomputerthrough
specialinputdevice
calledmicrophoneor
mic.
•Itworksintandemwitha
soundcard.
•Whenwespeakorinput
asoundthroughmic,the
soundcardtranslatesthe
electricalsignalfrom
microphoneintoa
digitizedformthatthe
computercanstoreand
process.

52. •Advantages
–Usefulforinputtingaudio/soundswhichcan’tbeinput
throughotheravailableinputdevices.
•Disadvantages
–Needsspecificandadditionalhardwarecalledsoundcard
whichmustbeinsertedinmotherboard.

53. Magnetic Ink Character Reader (MICR)
•Humanreadablecharactersareprintedon
documents(suchascheques)usingaspecial
magneticinkcalledmagneticink(thatcontainsiron
oxide).
•Specialfonthasbeensetforthesecharactersby
AmericanBankingAssociation.
•MICRreadsthesecharactersbymagnetizingtheink
andbyexaminingtheshapeofthecharacter.
•Theyaremainlyusedbybanks.

55. Magnetic Ink Character Reader

56. •Advantages
–DocumentspreparedbyMICRaredifficulttoforge.
–Documentscanstillbereadafterbeingfoldedorsplit
etc.
•Disadvantages
–MICRreadersandencodersareexpensive.
–Thesystemcanonlyacceptafewcharacters.
–Theycanonlybeusedbybankingindustrybecauseof
limitedsetofcharacters.

57. Scanner
•Ascannerisadevicelikephotocopier,whichcreatesan
electronicformofaprinted.
•Thescannerscanconvertanyimageintoelectronic
formbyshininglightontotheimageandsensingthe
intensityofthereflectionateverypoint.
•Scannerscomeinavarietyofsizesfromhand-heldto
desktopmodels.
–Hand-heldScannersareverysmallwhichcanbeheldina
hand.Thesearelessexpensivebutlesswide.
–Flatbedscannersarelargerandmoreexpensivescannersbut
theydefinitelycreatehigherqualityimages.Thesescanners
haveaflatsurfaceonwhichtheprintedimagetobescanned
isplaced.
–Drumscannersaremediumsizescannerswitharolling
drum.Thesheetisfedthroughthescannerssothatthe
drumrollsovertheentiresheettobescanned.

58. •Advantages
–Flatbedscannersareveryaccurateandcanproduceimages
withafarhigherresolutionthanadigitalcamera.
–Anyimagecanbeconvertedfrompaperintodigitalformat
andlaterenhancedandusedinothercomputerdocuments.
•Disadvantages
–Imagescantakeupalotofmemoryspace.
–Thequalityofthefinalimagedependsuponthequalityof
originaldocument.

59. Optical Character Reader (OCR)
•Anopticalcharacterreaderisusedtoreadcharacterof
specialtypefontsprintedonconventionalpaperwith
conventionalink(thesedaysOCR’sarecapableof
reading/identifyinghandwrittentextalso).
•Theprintedcharactersareexaminedbypassingthem
underastronglightandalenssystem,which
differentiateslight(noink)frominkedareas,anda
logicalsystemwhichattemptstodeterminewhichof
thepossiblecharactersisbeingexamined.
•Thesysteminactualusedependheavilyonthefact
thatonlyalimitednumberofcharactersinaparticular
fontareused,butsuchsystemsarestillquiteusefulas
theimageoftextisconvertedintoactualtextwhichis
editableinwordprocessor.

61. •Advantages
–OCRisfasterthantypingadocumentwhichisinprinted
formorhand-writtenform.
–Convertedtextiseditableinwordprocessor.
–Advancedversioncanevenrecreatetables,columnsand
evenproducewebpages.
•Disadvantages
–YouneedtobuyascannerandOCRsoftware.
–Itisnotcompletelyaccurateandtextwouldneedproof-
readingafterwards.

62. Optical Mark Reader (OMR)
•Inthismethod,specialpreprintedformsaredesignedwithboxes
whichcanbemarkedwithadarkpencilorink.
•Eachboxisannotateddistinctlysothattheuserclearly
understandswhatresponsehe/sheismarking.
•Suchadocumentisreadbyadocumentreader,calledoptical
markreader(OMR)whichtranscribedintoelectronicpulseswhich
aretransmittedtothecomputer.
•Suchdocumentsaremostlyusedinareaswhereresponsesare
oneoutofasmallnumberofalternativeandthevolumeofdatato
beprocessedislarger.
•OMRarebestsuitedfor:
–Objectivetypeanswerpapersinexaminationinwhichlargenumberof
candidatesappear.
–Varioustypesofsurveyswhereresponsescanberestrictedtooneor
moreoutofafewpossibilities.
–Orderformscontainingsmallchoiceofitems.
–Timesheetsofemployeeswherestartandstoptimesmaybemarked.

63. •Advantages
–Informationisenteredatitssourceandnofurther
transcriptionisrequiredtherebyminimizingunreliability
ofdata.
–Aquickandreliablewayofinputtinglargevolumesof
simpledata.
•Disadvantages
–Needforaccuratealignmentofprintingonforms
–Can’tbeusedforbulktext/numbersinput.

65. Smart Card Reader
•Theenhancedversionofcardswithmagneticstripsis
calledSmartCard.
•Thesmartcardcontainsamicroprocessorthatretains
certainsecurityandpersonaldatainitsmemoryatall
times.
•Thespecialreadermachinesthatcanreadinformation
onsmartcardarecalledsmart-cardreaders.
•Thesecardscanholdmoreinformation,havesome
processingcapabilityandarealmostimpossibleto
duplicate.
•Theycanserveasmulti-purposecardeg.AnATMcard,
creditcard,IDcard,electronic-cashcardetc.
•Application–banking,medicalrecords,security,etc.

67. Bar Code Reader
•Abarcodeisapatternofprintedbarsonvarious
typesofproducts.
•Abarcodereaderemitsabeamoflightwhich
reflectsoffthebarcodeimage.
•Alight-sensitivedetectorinthebarcodereader
thenidentifiesthebarcodeimagebyrecognizing
specialbarsatthebothendsoftheimage.
•Oncethebarcodeisidentified,thebarpatternis
convertedintoanumericcodethatcanbe
processedlaterinanymanner.

69. •Advantages
–Fastandreliablemethodofinputtingdata.
–Canevenreadfromcurvedorupsidedownsurfaces.
•Disadvantages
–Inputislimitedtoanumbercode.

70. Biometric Sensors
•Theyareusedforidentifyingaperson’sidentity.
•Biometricisatechnologythatverifiesaperson’s
identitybymeasuringaunique-to-the-individual
biologicaltrait.
•Biometrictechnologiesincludedynamicsignature
verification,retinal/irisscanning,DNA
identification,face-shaperecognition,voice
recognitionandfingerprintidentification.
•Biometricidentificationissuperiortolower
technologyidentificationmethodsincommonuse
today–namelypassword,PINnumbers,key-cards
andsmartcards.

73. Digital Camera (DigiCam)
•Acamerathatstoresimagesdigitallyratherthanrecording
themonfilmiscalleddigitalcamera.
•Onceapicturehasbeentaken,itcanbedownloadtoa
computersystem,andthenmanipulatedwithagraphics
programandprinted.
•Unlikefilmphotographs,whichhaveanalmostinfinite
resolution,digitalphotosarelimitedbytheamountof
memoryinthecamera,theopticalresolutionofthedigitizing
mechanism,andbytheresolutionofthefinaloutputdevice.
•Thebigadvantageofdigitalcameraisthatmakingphotosis
bothinexpensiveandfastbecausethereisnofilmprocessing.
•Adigitalcameradiffersfromwebcamerainthesensethatit
canbeoperateduponwithoutacomputersystemwhereasa
webcameraworkswithacomputersystem.

75. Web Camera
•Awebcamorwebcamera,isthelooselyusedterm
foranycamerathatgeneratesimagesthatcanbe
accessedbyanddisplayedonwebbrowsers
throughaserver.
•Awebcamisessentiallyacamerathatisconnected
toacomputereitherdirectlyorwirelessly.
•Awebcamgathersaseriesofdigitalimagesthatcan
bedisplayedremotelyonwebbrowsersremotely.

77. Output Devices
•Theoutputdeviceproduceoutputofthemachine
inhumanreadableform.
•Themostcommonoutputdevicesaremonitors,
printers,plotter,speakersetc.

78. Monitors
•Monitor(orscreen)isthemostcommonformof
outputfromacomputer.
•Itdisplaysinformationinasimilarwaytothatshown
onatelevisionscreen.
•Thepictureonamonitorismadeupofthousandsof
tinydotscalledpixels(pictureelements).
•Thequalityanddetailofthepictureonamonitor
dependsonthenumberofpixelsthatitcandisplay.
Thedenserarethepixels,thegreatertheclarityofthe
screenimage.
•ThetwomostcommontypesofmonitorareaLiquid
CrystalDisplay(LCD)andaCathodeRayTube(CRT)
monitor.

79. Cathode Ray Tube
•Itworksinthesamewayasatelevision.
•Itcontainsanelectrongunatthebackoftheglass
tubethatfireselectronatgroupsofphosphordots,
whichcoattheinsideofthescreen.
•Whentheelectronsstrikethephosphordotsthey
glowtogivethecolors.

81. Liquid Crystal Display(LCD) or TFT Display
•Liquidcrystalisthematerialusedtocreateeachpixel
onthescreen.
•Thematerialhasaspecialproperty–itcan‘polarize’
lightdependingontheelectricalchargeacrossit.This
featureallowsthepixelstobecreated.Eachtinycellof
liquidcrystalisapixel.
•TFT(orThinFilmTransistor)isthedevicewithineach
pixelthatsetsthecharge.
•SometimestheyarecalledLiquidCrystalDisplay
referringtothematerialtheyuseortheyarecalledTFT
displayreferringtothetinytransistorsthatmakethem
work.
•LCDusemuchlesspowerthananormalmonitor.

83. •Advantages
–Relativelycheapandreliable.
–Candisplaytextandgraphicsinawiderangeofcolors.
–Aseachtaskisprocessed,theresultscanbedisplayed
immediatelyonthescreen.
•Disadvantages
–Nopermanentcopytokeep–theresultswilldisappear
whenthecomputerisswitchedoff.
–Unsuitableforuserswithvisualproblems.
–CRTscreensaremadeofglassandcanbeveryfragile
(easilybrokerordamaged).

84. Printers
•Itisanoutputdeviceusedforcreatingpapercopies
ofoutputfromthecomputer.
•Printerscanproducetextandimagesonpaper.
•Veryspecialistprinterscanalsoprintonplasticor
eventextilessuchasT-shirts.
•Printerscanbedividedintotwodifferent
categories-
–ImpactPrinters:Intheseprinters,thereismechanical
contactbetweentheprintheadandpaper.
–Non-impactPrinters:Intheseprinters,thereisno
mechanicalcontactbetweentheprintheadandpaper.

85. Impact Printers
•Theimpactprinterscomeinlotofvarietiessuchas
dotmatrixprinters,lineprinters,drumprinters,
daisywheel.
•DotMatrixPrinters
–Itisthemostpopularserialprinteri.e.itprintsone
characteratatime.
–Theprintheadcontainsaverticalarrayofpins.
–Astheheadmovesacrossthepaper,selectedpinsfire
againstaninkedribbontoformapatternofdotsonthe
paper.

87. •Advantages
–Lowoperatingcosts
–Canprintoncontinuousstationary
–Theyarerobustandcanbeusedindirtyorharsh
conditions–youoftenseethemingaragesorfactories.
–Usingcarbonatedpaper,DMP’scancreatecarbon
copies.
•Disadvantages
–Lowresolution–printqualityistoopoortoproduce
importantdocumentsforcustomersormanagement.
–Veryslow–canbelessthan100charactersperminute.
–Verynoisy–can’tbeusednearaphone.
–Cannotproducecolorcopies.

88. Non Impact Printers
•Thenaturallimitationofspeedinelectromechanical
devicesandcostconsiderationshaveledtothe
developmentofprinterscallednon-impactprinters.
•InkjetPrinters
–Aprinterthatfiresextremelysmalldropletsofinkonto
papertocreateimpressionoftextorimage.
–Itdirectsahigh-velocitystreamofinktowardsthepaper.
–Thisstreamisdeflected,generallybypassingitthrough
anelectrostaticfieldsuchasthatusedtodeflectbeams
inoscilloscopes.
–Insomesystemstheinstreamisbrokenintodropletsby
anultrasonictransducer.

89. •BubbleJetPrinters
–Inabubblejetprinter,tinyresistorscreateheat,andthis
heatvaporizesinktocreateabubble.
–Theexpansionthatcreatesthebubblecausesadroplet
toformandejectfromtheprinthead.
–Atypicalbubblejetprintheadhas64to128tiny
nozzles,andallofthemcanfireadroplet
simultaneously.

91. •Advantages
–Goodresolution–usually300-600dotsperinch.Thismeansthey
canprintgoodqualityresults.
–Cheaptobuy.
–Small–idealforhomeoroffice.
–Lighterinweightthanotherprinters
–FastcomparedtoaDotMatrixPrinter
–Veryquiet
–Canprintblackandwhiteandcoloronthesamepage.
•Disadvantages
–Slowcomparedtoalaserprinter
–Colorprintingcantake25-30secondseachpage
–Overall,thecartridgescostmoreperpagethanlaserprinter
cartridges
–Cartridgesneedtobereplacedmorefrequentlythanthoseofa
laserprinter.
–Outputisinkbasedandwillsmudgeiftheprintoutgetswet.
–Ifleftunusedforlongperiodsoftime,thecartridgescaneasilydry
out.

92. Plotters
•Plottersaretheoutputdevicesthatproducegood
qualitydrawingsandgraphs.
•Twotypes:
–Drumplotter:
•Theoutputpaperismountedonarotatingdrum.
•Apencapableoflinearmotionismountedonacarriage.
•Thedrumcanrotateineitherclockwiseoranti-clockwisedirection
underthecontrolofplottinginstructionssentbythecomputer.
•Thepencanmoveineitherdirection–lefttorightorrighttoleftor
upwardsordownwards.
–Flat-bedplotter:
•Itconsistsofastationaryhorizontalplottingsurfaceonwhichpaper
isfixed.
•Thepenismountedonacarriagewhichcanmovehorizontallyor
verticallyorleftwardsorrightwards.

94. •Advantages
–Drawingsareofthesamequalityasifanexpertdrew
them.
–Largersizesofpapercanbeusedthanwouldbefound
onmostprinters.
•Disadvantages
–Plottersareslowerthanprinters,drawingeachline
separately.
–Theyareoftenmoreexpensivethanprinters.
–Thereisalimittotheamountofdetailstheseplotters
canproduce.

95. Speakers
•Asthesoundcapabilitieshavebecomeastandardpart
ofacomputersystem,speakershavebecomekey
sound-outputsystems.
•Acomputersystemhavingsoundcapabilitiescannot
workwithoutasoundcard.
•Speakersreceivethesoundinformofelectriccurrent
fromthesoundcardandthenconvertittosound
format.
•Speakersreceiveconstantlychangingelectriccurrent
fromsoundcard.Thiscurrentistransferredtoa
magnetwhichpushesthespeakercorebackandforth.
Thiswaypressurevibrationsaregeneratedthatcreate
sound.

96. Memory Devices
•Themainmemoryortheinternalmemoryorthe
primarymemoryisalsoknownasImmediateAccess
Store(IAS).
•TheIASorthemainmemoryholdsthedataand
programsneededatthatinstantbyCPU.
•TheCPUreadsthedataandprogramskepton
secondarystorageintothemainmemory,temporarily
i.e.aslongastheyarebeingprocessed.
•TheCPUneedstodothisbecausesecondarystorageis
muchtooslowerthanthemainmemoryandtheCPU.
•Thus,whenthedataandprogramsareavailablein
mainmemorywhichisfasterthansecondarystorage,
theCPU’stimeisnotwasted.

97. Units of Memory
•Abinarynumberiseither0(representingOFF/lowvoltage)or1(representing
ON/highvoltage),andisknownasbit,whichisshortformforbinarydigit.
•Internallycharactersarerepresentedthroughagroupofbitsdependingupon
encodingschemebeingused.
•ASCII(AmericanStandardCodeforInformationInterchange)encodingscheme
representsacharacterasagroupof8bitsorabyte.
•Unicodeschemerepresentsacharacterasagroupof16bitsor2bytes.
•Byteisthesmallestmeasuringunitofmemory.
•Theothermeasuringunitsofmemoryare–
–4bits = 1nibble
–8bits = 1byte
–2
10
or1024bytes= 1Kilobyteor1KB
–2
10
or1024KB = 1Megabyteor1MB
–2
10
or1024MB = 1Gegabyteor1GB
–2
10
or1024GB = 1Terabyteor1TB
–2
10
or1024TB = 1Petabyteor1PB
•Eachkeyboardcharacterisrepresentedthroughatleast1byte.

98. Parts of Memory
•TheCPUisattachedtotwokindsofmemories:RAM,whichis
volatileandROM,whichisnon-volatile.
–RandomAccessMemory(RAM)
•TheRAMisintheformofRAMchips.
•ThedataisheldinRAM,buttemporarilythedatadisappearsifthepoweris
switchedoff.
•RAMisvolatilememory.
–ReadOnlyMemory(ROM)
•TheROMisalsointheformofchips.
•ThedatastoredonROMisnoterasedwhenthepowerisswitchedoffi.e.it
ispermanent.
•ROMisanon-volatilememory.
•ProgramsrelatedtotheoperatingsystemarestoredonROMchipswhen
thecomputerismanufactured.
•TheinformationstoredonROMisusuallyusedtotellthecomputerhowto
loadtheoperatingsystemwhenitisswitchedonorre-booted.
–BothRAMandROMarereferredtoasImmediateAccessStorage
(IAS)becauseCPUcanaccessthedatasoquicklycomparedto
datainbackingstorage(thesecondarystorage)

99. The Main Memory
(Primary Memory)
•The main memory can be divided into two parts :
–RAM (Random Access Memory)
–ROM (Read Only Memory)
99

100. •Random Access Memory
–InRAMthememorycellscanbeaccessedforinformation
transferfromanydesiredrandomlocation.
–Theprocessoflocatingawordinmemoryisthesameand
requiresanequalamountoftime,thusthename“random
access”.
–ThemaindrawbackofRAMisthatitisavolatilememoryi.e.
whenthepowergoesoff,contentsofRAMgetserased.
–TheRAMchipsinacomputercanbeoftwobasictypes:
•DynamicRAM(DRAM)and
•StaticRAM(SRAM)
100

101. Dynamic RAM (DRAM)
•Itconsistsofatransistorandcapacitorthat’scapableofstoringan
electriccharge.
•Dependingontheswitchingactionofthetransistor,thecapacitor
eithercontainsnocharge(0bit)ordoesholdacharge(1bit).
•Sincethechargeonthecapacitortendstoleakoff,provisionis
madetoperiodicallysegmentorrefreshthestoragecharge.Thus,
dynamicRAMprovidedvolatilestoragei.e.itscontentsarelostin
theeventofpowerfailure.
•AtypicalDRAMcellconsistsofonlytwoelements-
–aMOSFET(metalOxideSemiconductorFieldEffectTransistor)switch,
and
–aCapacitorstoringabit.
•DRAMcellconsumesverylesspowerandisabletosustainhigh
frequencyofswitchingoperations.
•Today’sDRAMchipshaveaccesstimerangingfrombelow7to70
nanoseconds.
–Theamountoftimetakentoproducedatarequiredfrommemory,from
thestartofaccessuntiltheavailabilityofdata,iscalledMemoryAccess
Time.
101

102. TYPES OF DRAM
•EDO(ExternalDataOut)DRAM–AnEDODRAMcellkeepsitsdatavalid
untilthememoryreceivesanadditionalsignal.Ithasadual-pipeline
architecture,whichallowsthememorycontrollertosimultaneouslyread
newdatawhiledischargingtheold.Asaresultthesystemdoesnothaveto
waitforaseparatereadcycle,butcanreadorwritedataimmediatelyas
soonasaddressbitsaresuppliedtothechip.
•SynchronousDRAM(SDRAM)–Becauseofmultiplexing,EDODRAMchips
cannotoperateinlock-stepwiththeirhostmicroprocessors.Such
asynchronousmemoryperformanceskeepthememorybusspeedlimited
to66MHz.SDRAMweredesignedtooperateinsynchronizationwiththe
hostmicroprocessor,deliverdataineachclockcycleandrunthememory
busfasterthan66MHz.
•RambusDRAM(RDRAM)–Itisfairlyfastandithastriedtoaddresssome
ofthecomplexelectricalandphysicalproblemsinvolvedwithmemory.The
Rambusprotocoldoesnotmultiplexorsharecontrolinformationonthe
databus,ratheritcreatesanindependentcontrolandaddressbussplitinto
twogroupsofpinsforrowandcolumncommands,anddataistransmitted
acrossa16-bitwidedatabus.
•DoubleDataRate(DDR)SDRAM–UnlikeSDRAMmemorythatsupports
oneoperationineachclockcycle,DDRSDRAMmemorycandotwo
operationsperclockcycle,therebydoublingthememorybandwidthover
thecorrespondingsingle-data-rateSDRAM.
102

103. STATIC RAM (SRAM)
•Itisalsovolatilebutaslongastheyaresupplied
withpower,theyneednospecialregeneratorcircuit
toretainthestoreddata.
•Iteventuallyconsistsofinternalflip-flops(aflip-flop
isabinarycellcapableofstoringonebitof
information)thatstorethebinaryinformation.
•SRAMstakeupmorespaceforagivenstorage
capacitythandoDRAMs.
•SRAMsarethususedinspecializedapplications
whileDRAMsareusedintheprimarystorage
sectionsofmostcomputers.
•Itiseasiertouseandhasshorterreadandwrite
cyclescomparedtoDRAM. 103

104. •ReadOnlyMemory(ROM)
–Itisamemoryunitthatperformsthereadoperation
only,itdoesnothaveawritecapability.
–ThebinaryinformationinaROMismadepermanent
duringthehardwareproductionoftheunitandcannot
bealteredbywritingdifferentwordsintoit(non-
volatile).
–Itisanon-volatilememoryi.e.whenthepowergoes
off,contentsofROMstayswithintheunit.
–ROMsareusedforapplicationsinwhichitisknown
thattheinformationneverneedstobealtered.
–ROMarehoweverslowerthanRAM.
104

105. TYPES OF ROM
•ProgrammableReadOnlyMemory(PROM)–AROMthatcanbe
programmedtorecordinformationusingafacilityknownasPROM-
programmer.Oncethechiphasbeenprogrammed,therecorded
informationcannotbechangedi.e.PROMbecomessameasROM.
•ErasablePROM(EPROM)–ItisanothertypeofROMthatbeerasedandthe
chipcanbeprogrammedtorecorddifferentinformationusingaspecial
PROM-programfacility.Erasureisachievedbyexposingthechipto
ultravioletlight.WhenanEPROMisinuse,informationcanonlybe“read”
andtheinformationremainsonthechipuntilitiserased.EPROMareof
twotypes–UPROM(ultravioletPROM)andEAPROM(ElectricallyAlterable
PROM).
•ElectricallyErasablePROM(EEPROM)–ThistypeofROMcanbe
programmedanderasedbyelectricalsignals.Informationloadedinthis
memorycanberetainedformanyyearswithoutanypowersupplied.One
ofitsapplicationisasaback-upofRAMmemorywhosecontentsarelostin
apowerfailure.Whenpowerisreturned,theEEPROMmemorycanbeused
toreplacethelostcontentsoftheRAMmemoryandthemicrocomputer
cancontinueworkingjustasifnothinghadhappened.
105

106. Cache Memory
•TheCacheMemoryisahigh-speedmemoryavailableinsideCPUinorder
tospeedupaccesstodataandinstructionsstoredinRAMmemory.
•Itcanbeeitherareservedsectionofmainmemoryoranindependent
high-speedstoragedevice.
•Amemorycache,sometimescalledacachestoreorRAMcache,isa
portionofmemorymadeofhighspeedstaticRAM(SRAM)insteadofthe
slowerandcheaperdynamicRAM(DRAM)usedformainmemory.
•Memorycachingiseffectivebecausemostprogramsaccessthesamedata
orinstructionsoverandoveragain.Bykeepingasmuchofthis
informationinSRAM,thecomputeravoidsaccessingtheslowerDRAM.
•Wheneversomedataisrequired,theCPUfirstlooksinthecache,ifitis
thereornot.Ifthedataisfoundincache,CPUdoesnotaccessmemory
andhencetheprocessbecomesveryfast.
•Whendataisfoundinthecache,itiscalledacachehit,andthe
effectivenessofacacheisjudgedbyitshitrate.Manycachesystemusesa
techniqueknownassmartcaching,inwhichthesystemcanrecognize
certaintypesoffrequentlyuseddata.
106

107. TYPES OF CACHE MEMORY
•Level1(L1)Cache
•Level2(L2)Cache
–TheL1cacheisbuiltinsidetheCPUpackagewhiletheL2
cacheisexternaltotheCPUandresidesonthe
motherboard.LikeL1caches,L2cachesarecomposedof
SRAMbuttheyaremuchlarger.
–Insixthgenerationprocessors(fromPentiumProonwards),
bothL1andL2cachehavebeenintegratedwithintheCPU
packagetoreduceaccesstimeandimprovesystem
performance.
–TheL2cacheonthemotherboardworksatmotherboardbus
speedwhiletheL1cacheinsidetheCPUworksathalfthe
CPUclockspeed. 107