Unit-1-Computer-Technologies

Unit1ComputerTechnologiesIntroductionThecentralandessentialingredientofCAD/CAMisthedigitalcomputer.Itsinherentspeedandstoragecapacityhavemadeitpossibletoachievetheadvancesinimageprocessing,real-timeprocesscontrol,andamultitudeofotherimportantfunctionsthataresimplytoocomplexandtime-consumingtoperformmanually.TounderstandCAD/CAM,itisimportanttobefamiliarwiththeconceptsandtechnologyofthedigitalcomputer.Themoderndigitalcomputerisanelectronicmachinethatcanperformmathematicalandlogicalcalculationsanddataprocessingfunctionsin组成部分ComputerAidedDesignComputerAidedManufacturing数字的、计数的天生的、固有的逻辑的accordancewithapredeterminedprogramofinstructions.Thecomputeritselfisreferredtoashardware,whereasthevariousprogramsarereferredtoassoftware.Therearethreebasichardwarecomponentsofageneral-purposedigitalcomputer:￭Centralprocessingunit（CPU）￭Memory￭Input/output（I/O）sectionTherelationshipofthesethreecomponentsisillustratedinFig.1.1.Thecentralprocessingunitisoftenconsideredtoconsistoftwosubsections:acontrolunitandanarithmetic-logicunit（ALU）.Thecontrolunitcoordinatestheoperationsofalltheothercomponents.Itcontrolstheinputandoutputof内存多种用途的输入/输出接口算术逻辑运算器中央处理器informationbetweenthecomputerandtheoutsideworldthroughtheI/Osection,synchronizesthetransferenceofsignalsbetweenthevarioussectionsofthecomputer,andcommandstheothersectionsintheperformanceoftheirfunctions.Thearithmetic-logicunitcarriesoutthearithmeticandlogicmanipulationsofdata.Itadds,subtracts,multiplies,divides,andcomparesnumbersaccordingtoprogrammedinstructions.Thememoryofthecomputeristhestorageunit.ThedatastoredinthissectionarearrangedintheformofwordswhichcanbeconvenientlytransferredtotheALUorI/Osectionforprocessing.Finally,theinput/outputprovidesthemeansforthecomputertocommunicatewiththeexternalworld.Thiscommunicationisaccomplishedthroughperipheralequipmentsuchasreaders,printers,andprocessinterfacedevices.Thecomputermayalsobeconnectedtoexternalstorageunits（e.g.,tapes,disks,etc.）throughtheI/Osectionofthecomputer.使同步发生外围的Thesoftwareconsistsoftheprogramsandinstructionsstoredinmemoryandinexternalstorageunits.Itisthesoftwarethatassignsthevariousfunctionswhichtheuserdesiresthesystemtoaccomplishtothecomputer.Theusefulnessofthecomputerliesinitsabilitytoexecutetheinstructionsquicklyandaccurately.Becausethecontentsofthecomputer’smemorycanbeeasilychanged,andthereforedifferentprogramscanbeplacedintomemory,thedigitalcomputercanbeusedforawidevarietyofapplications.Regardlessoftheapplication,thecomputerexecutestheprogramthroughitsabilitytomanipulatedataandnumbersintheirmostelementaryform.Thedataandnumbersarerepresentedinthecomputerbyelectricalsignalswhichcantakeonoftwoalternativestates.Thisformofrepresentationiscalledthebinarysystem.Themorefamiliardecimalnumbersystemandawholehostofsoftwarelanguagescanutilizethebinarysystemtopermitcommunicationbetween二进制的十进制的computersandhumanbeings.CentralProcessingUnit（CPU）Thecentralprocessingunit（CPU）regulatestheoperationofallsystemcomponentsandperformsthearithmeticandlogicaloperationsonthedata.Toaccomplishthesefunctions,theCPUconsistsoftwooperatingunits:￭Controlunit￭Arithmetic-logicunit（ALU）Thecontrolunitcoordinatesthevariousoperationsspecifiedbytheprograminstructions.Theseoperationsincludereceivingdatawhichenterthecomputeranddecidinghowandwhenthedatashouldbeprocessed.Thecontrolunitdirectstheoperationofthearithmetic-logicunit.ItsendsdatetotheALUandtellstheALUwhatfunctionstoperformonthedataandwheretostoretheresults.Thecapabilityofthecontrolunittoaccomplishtheseoperationsis控制、管制指定providedbyasetofinstructionscalledanexecutiveprogramwhichisstoredinmemory.Thearithmetic-logicunitperformsoperationssuchasaddition,subtractions,andcomparisons.Theseoperationsarecarriedoutondatainbinaryform.Thelogicsectioncanalsobeusedtoalterthesequenceinwhichinstructionsareexecutedwhencertainconditionsareindicatedandtoperformotherfunctions,suchaseditingandmaskingdataforarithmeticoperations.Boththecontrolunitandthearithmetic-logicunitperformtheirfunctionsbyutilizingregisters.Computerregistersaresmallmemorydevicesthatcanreceive,hold,andtransferdata.Eachregisterconsistsofbinarycellstoholdbitsofdata.Thenumberofbitsintheregisterestablishesthewordlengthwithwhichthecomputeriscapableofhandling.Thenumberofbitsperwordcanbeasfewas4（earlymicrocomputers）orasmanyas64（largescientificcomputers）.顺序、次序、序列屏蔽寄存器确定ComputerProgrammingLanguagesThebinarynumbersystemcouldbeusedtorepresentanydecimalnumber,alphabeticletter,orothercommonsymbol.Dataandinstructionsarecommunicatedtothecomputerintheformofbinarywords.Inexecutingaprogram,thecomputerinterpretstheconfigurationofbitsasaninstructiontoperformelectronicoperationssuchasadd,subtract,loadintomemory,andsoforth.Thesequenceofthesebinary-codedinstructionsdefinesthesetofcalculationsanddatamanipulationsbywhichthecomputerexecutestheprogram.Thebinary-codedinstructionsthatcomputerscanunderstandarecalledmachinelanguage.Unfortunately,binary-codedinstructionsanddataareverydifficultforhumanprogrammerstoreadorwrite.Also,differentmachinesusedifferentmachinelanguages.Tofacilitatet