MicroprocessorsAmicroprocessorisacomputationenginethatisfabricatedonasinglechip.ThefirstmicroprocessorwastheIntel4004,introducedin1971.The4004wasnotverypowerfulallitcoulddowasaddandsubtract,anditcouldonlydothat4bitsatatime.Butitwasamazingthateverythingwasononechip.Priortothe4004,engineersbuiltcomputerseitherfromcollectionsofchipsorfromdiscretecomponents.The4004poweredoneofthefirstportableelectroniccalculators.ThefirstmicroprocessortomakeitintoahomecomputerwastheIntel8080,acomplete8-bitcomputeronthechip,introducedin1974.ThefirstmicroprocessortomakearealsplashinthemarketwastheIntel8088,introducedin1979andincorporatedintotheIBMPC.ThePCmarketmovedfromthe8088tothe80286tothe80386tothe80486tothePentiumtothePentiumIItothePentiumIIItothePentium4.AllofthesemicroprocessorsaremadebyIntelandallofthemareimprovementsonthebasicdesignofthe8088.ThePentium4canexecuteanypieceofcodethatranontheoriginal8088,butitdoesitabout5,000timesfaster!ThefollowingtableshowsthedifferencesbetweenthedifferentprocessorsthatIntelhasintroducedovertheyears.Table1.2NameDateTransistorsMicron1ClockspeedDatawidth2MIPS3808019746,00062MHz8bits0.648088197929,00035MHz16bits8-bitbus0.33802861982134,0001.56MHz16bits1803861985275,0001.516MHz32bits58048619891,200,000125MHz32bits20Pentium19933,100,0000.860MHz32bits64-bitbus100PentiumII19977,500,0000.35233MHz32bits64-bitbus300PentiumIII19999,500,0000.25450MHz32bits64-bitbus510Pentium4200042,000,0000.181.5GHz32bits64-bitbus1,700Fromthistableyoucanseethat,ingeneral,thereisarelationshipbetweenclockspeedandMIPS.Themaximumclockspeedisafunctionofthemanufacturingprocessanddelayswithinthechip.ThereisalsoarelationshipbetweenthenumberoftransistorsandMIPS.Forexample,the8088clockedat5MHzbutonlyexecutedat0.33MIPS(aboutoneinstructionper15clockcycles).Modernprocessorscanoftenexecuteatarateoftwoinstructionsperclockcycle.Thatimprovementisdirectlyrelatedtothenumberoftransistorsonthechip.InsideaMicroprocessorAmicroprocessorexecutesacollectionofmachineinstructionsthattelltheprocessorwhattodo.Basedontheinstruction,amicroprocessordoesthreebasicthings:1.UsingitsALU(Arithmetic/LogicUnit),amicroprocessorcanperformmathematicaloperationslikeaddition,subtraction,multiplicationanddivision.ModernMicroprocessorscontaincompletefloatingpointprocessorsthatcanperformextremelysophisticatedoperationsonlargefloatingpointnumbers.2.Amicroprocessorcanmovedatafromonememorylocationtoanother.3.Amicroprocessorcanmakedecisionsandjumptoanewsetofinstructionsbasedonthosedecisions.Thesemaybeverysophisticatedthingsthatamicroprocessordoes,butthoseareitsthreebasicactivities.Thefollowingdiagramshowsanextremelysimplemicroprocessorcapableofdoingthosethreethings:Thismicroprocessorhasanaddressbusthatsendsanaddresstomemory,adatabusthatcansenddatatomemoryorreceivedatafrommemory,anRD(read)andWR(write)linetotellthememorywhetheritwantstosetorgettheaddressedlocation,aclocklinethatletsaclockpulsesequencetheprocessorandareset4linethatresetstheprogramcountertozero(orwhatever)andrestartsexecution.Andletsassumethatboththeaddressanddatabusesare8bitswidehere.Herearethecomponentsofthissimplemicroprocessor(Figure1.1):Figure1.11.RegistersA,BandCaresimplylatchesmadeoutofflipflops.2.TheaddresslatchisjustlikeregistersA,BandC.3.Theprogramcounterisalatchwiththeextraabilitytoincrementby1whentoldtodoso,andalsotoresettozerowhentoldtodoso.4.TheALUcouldbeassimpleasan8-bitadder,oritmightbeabletoadd,subtract,multiplyanddivide8bitvalues.Letsassumethelatterhere.5.ThetestregisterisaspeciallatchthatcanholdvaluesfromcomparisonsperformedintheALU.AnALUcannormallycomparetwonumbersanddetermineiftheyareequal,ifoneisgreaterthantheother,etc.Thetestregistercanalsonormallyholdacarrybitfromthelaststageoftheadder.Itstoresthesev