Computer 　　Ageneral-purposemachinethatprocessesdataaccordingtoasetofinstructionsthatarestoredinternallyeithertemporarilyorpermanently.Thecomputerandallequipmentattachedtoitarecalledhardware.Theinstructionsthattellitwhattodoarecalled"software."Asetofinstructionsthatperformaparticulartaskiscalleda"program"or"softwareprogram." 　　WhataComputerDoes 　　Theinstructionsintheprogramdirectthecomputertoinput,processandoutputasfollows: 　　Input/Output 　　Thecomputercanselectivelyretrievedataintoitsmainmemory(RAM)fromanyperipheraldevice(terminal,disk,tape,etc.)connectedtoit.Afterprocessingthedatainternally,thecomputercansendacopyoftheresultsfromitsmemoryouttoanyperipheraldevice.Themorememoryithas,themoreprogramsanddataitcanworkwithatthesametime. 　　Storage 　　Byoutputtingdataontoamagneticdiskortape,thecomputerisabletostoredatapermanentlyandretrieveitwhenrequired.Asystem'ssizeisbasedonhowmuchdiskstorageithas.Themoredisk,themoredataareimmediatelyavailable. 　　Processing(The3C's) 　　Thecomputerperformsallprocessingby"calculating,""comparing"and"copying"thedatastoredinitsmemory(RAM). 　　Calculate 　　Thecomputercanperformanymathematicaloperationondatabyadding,subtracting,multiplyinganddividingonesetwithanother. 　　Compare 　　Thecomputercananalyzeandevaluatedatabymatchingitwithsetsofknowndatathatareincludedintheprogramorcalledinfromstorage. 　　Copy 　　Thecomputercanmovedataaroundtocreateanykindofreportorlistinginanyorder. 　　Calculate,CompareandCopy 　　Bycalculating,comparingandcopying,thecomputeraccomplishesallformsofdataprocessing.Forexample,recordsaresortedintoaneworderbycomparingtworecordsatatimeandcopyingtherecordwiththelowervalueinfrontoftheonewiththehighervalue. 　　Thecomputerfindsonecustomeroutofthousandsbycomparingtherequestedaccountnumbertoeachrecordinthefile.Thequerystatement:SUMSALARYFORTITLE="NURSE"causesthecomputertocomparethetitlefieldineachrecordforNURSEandthenadd(calculate)thesalaryfieldforeachmatch. 　　Inwordprocessing,insertinganddeletingtextisaccomplishedbycopyingcharactersfromoneplacetoanother.