Introduction
Inthecentralprocessingunit,theaccumulator(accumulator)isaregisterusedtostoreintermediateresultsgeneratedbycalculations.Ifthereisnoregisterlikeanaccumulator,thenaftereverycalculation(addition,multiplication,shift,etc.),theresultmustbewrittenbacktothememory,andmaybereadbackimmediately.However,thespeedofaccesstothemainmemoryisslowerthantheaccessfromthearithmeticlogicunittotheaccumulatorwithadirectpath.
Thestandardexampleistoaddupthenumbersinacolumn.Atthebeginningtheaccumulatorissettozero,andeachnumberisaddedtotheaccumulatorinsequence.Whenallthenumbersareadded,theresultiswrittenbacktothemainmemory.
Today'sCPUusuallyhasmanyregisters,allormostofthemcanbeusedasaccumulators.Forthisreason,theterm"accumulator"isabitold.Thistermisalmostnotusedinmicroprocessorregisters.Forexample,thesymbolbeginningwith"A"inthenameofarithmeticregisterisderivedfromthehistoricalfactorof"accumulator"(sometimesitisnotconsidered"arithmetic").Itmayalsobeconfusingthattheprefix"A"inthenameoftheregisteralsomeans"address",suchastheMotorola68000family.
Early4-bitand8-bitmicroprocessorstypicallyhadasingleaccumulator.The8051microcontrollerhastwoaccumulators:amasteraccumulatorandaslaveaccumulator.Theslaveaccumulatorisonlyusedformultiplication(MULAB)anddivision(DIVAB).The16-bitresultofthemultiplicationisplacedintwo8-bitaccumulators.Duringdivision,thequotientisplacedinthemasteraccumulator,andtheremainderisplacedintheslaveaccumulator.Thedirectsuccessorsof8008,8080and8086,pioneeredthex86instructionsetarchitectureandstillusetwoaccumulators:themasteraccumulatorEAXandtheslaveaccumulatorEDXareusedforlargenumberoperationsinmultiplicationanddivision.Forexample,MULECXwillmultiplytwo32-bitregistersECXandEAX,andthe64-bitresultwillbeplacedinEAXandEDX.Butotherarithmetic-logicinstructions(ADD,SUB,CMP,AND,OR,XOR,TEST)otherthanMULandDIVcanuse8registers:EAX,ECX,EDX,EBX,ESP,EBP,ESI,EDIasThedestinationoperand(thatis,thelocationwheretheresultisstored).
CentralProcessingUnit
CentralProcessingUnit(English:CentralProcessingUnit,abbreviation:CPU),isoneofthemainequipmentofacomputer,whosefunctionismainlytointerpretcomputerinstructionsandprocessdataincomputersoftware.Computerprogrammabilitymainlyreferstotheprogrammingofthecentralprocessingunit.Thecentralprocessingunit,internalmemoryandinput/outputdevicesarethethreecorecomponentsofmoderncomputers.Beforethe1970s,thecentralprocessingunitwascomposedofmultipleindependentunits.Later,thecentralprocessingunitmadeofintegratedcircuitswasdeveloped.Thesehighlycontractedcomponentsaretheso-calledmicroprocessors.ThemostcomplexcircuitofthebranchedcentralprocessingunitcanbeMakeasingletinyandpowerfulunit.
Inabroadsense,thecentralprocessingunitreferstoaseriesoflogicalmachinesthatcanexecutecomplexcomputerprograms.Thisvaguedefinitioneasilyincludesearlycomputersbeforethename"CPU"wascommonlyused.Inanycase,atleastsincetheearly1960s(Weik1961),thisnameanditsabbreviationhavebeguntobewidelyusedinthecomputerindustry.Althoughcomparedwiththeearlydays,the"centralprocessingunit"hasgreatlydevelopedinphysicalform,designandmanufacturing,andtheexecutionofspecifictasks,butitsbasicoperatingprincipleshavenotchanged.
Earlycentralprocessingunitsareusuallycustomizedforlarge-scaleandapplication-specificcomputers.However,thisexpensivemethodofcustomizingCPUsforspecificapplicationshaslargelygivenwaytodevelopingcheap,standardized,andsuitableprocessorsforoneormorepurposes.Thisstandardizationtrendbeganintheeraofmainframesandmicrocomputerscomposedofasingletransistor,andacceleratedwiththeadventofintegratedcircuits.ICallowsmorecomplexcentralprocessingunitstobedesignedandmanufacturedinasmallspace(ontheorderofmicrometers).Thestandardizationandminiaturizationofcentralprocessingunitshavemadethistypeofdigitalequipmentandelectronicpartsappearmorefrequentlyinmodernlifethancomputersdedicatedtolimitedapplications.Modernmicroprocessorsappearineverythingfromcarstomobilephonestochildren'stoys.
Computer:arithmetic,logic(components:arithmeticlogicunit,accumulator,registerset,pathconverter,databus);
Controller:reset,enable(components:counter,instructionregister,instructiondecoder,statusregister,clockgenerator,micro-operationsignalgenerator).
Computermemory
Computermemory(English:Computermemory)isakindofstoragedatamadeusingsemiconductortechnologyElectronicequipment.Thedataintheelectroniccircuitisstoredinabinarymanner,andeachstorageunitofthememoryiscalledamemoryelement.
Memory,alsoknownasmemory,isastoragespacethatcanbedirectlyaddressedbytheCPUandismadeofsemiconductordevices.Thememoryischaracterizedbyfastaccessspeed.Memoryisthemaincomponentofthecomputer,itisrelativetotheexternalmemory.Theprogramsweusuallyuse,suchasWindowsoperatingsystem,typingsoftware,gamesoftware,etc.,aregenerallyinstalledonexternalstoragesuchasharddisks.Toreallyuseitsfunctions,weusuallyenteraparagraphoftextorplayagame,whichisactuallydoneinmemory.Justlikeinastudyroom,thebookshelvesandbookcasesstoringbooksareequivalenttotheexternalstorageofthecomputer,andthedeskwhereweworkisthememory.Usuallywestorealargeamountofdatatobestoredpermanentlyontheexternalmemory,andputsometemporaryorasmallamountofdataandprogramsonthememory.Ofcourse,thequalityofthememorywilldirectlyaffecttheoperatingspeedofthecomputer.
ArithmeticLogicUnit
ArithmeticLogicUnit(English:ArithmeticLogicUnit,ALU)istheexecutionunitofthecentralprocessingunit,Isthecorecomponentofallcentralprocessingunits.Itisanarithmeticlogicunitcomposedofandgatesandorgates.Themainfunctionistoperformbinaryarithmeticoperations,suchasaddition,subtractionandmultiplication(excludingintegerdivision).Basically,inallmodernCPUarchitectures,binaryisrepresentedintheformoftwo'scomplement.
See
Virtualmemory
Memoryhierarchy