Ageneral-purposemachinethatprocessesdataaccordingtoasetofinstructionsthatarestoredinternallyeithertemporarilyorpermanently.Thecomputerandallequipmentattachedtoitarecalledhardware.Theinstructionsthattellitwhattodoarecalled"software."Asetofinstructionsthatperformaparticulartaskiscalleda"program"or"softwareprogram."
WhataComputerDoes
Theinstructionsintheprogramfromthecomputertoinput,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.