chapter 7 storage1. storage 课件

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1、CHAPTER7StorageStorageWhenacomputerisfirstswitchedon,itneedstoloaduptheBIOS(BasicInput/OutputSystem)andbasicinstructionsforthehardware.ThesearestoredinROM(ReadOnlyMemory).Thistypeofmemoryiscallednon-volatilebecauseitretainsthedata.DatastoredinROMremainsthereevenw

2、henthecomputerisswitchedoff.ROMcanbefoundonthemotherboard.ReadOnlyMemory(ROM)ComputersstoretemporarydataintheRAM(RandomAccessMemory).Thesecouldbeoperatinginstructions,loosebitsofdataorcontentfromprogramsthatarerunning.ThecontentsofRAMareconstantlyrewrittenastheda

3、taisprocessed.Whenthecomputerisswitchedoff,allthedataisclearedfromtheRAM.Thistypeofmemoryiscalledvolatilebecauseitonlystoresthedatawhilstthecomputerisswitchedon.RAMsticksarefoundonthemotherboard.RandomAccessMemory(RAM)RAMandROMComputersneedbackingstorageoutsideth

4、eCPUtostoredataandprogramsnotcurrentlyinuse.Therearethreemaintypesofstoragedevice:Thosethatstoredatabymagnetizingaspecialmaterialthatcoatsthesurfaceofadisk.Thosethatstoredatausingopticaltechnologytoetchthedataontoaplastic-coatedmetaldisk.Laserbeamsarethenpassedov

5、erthesurfacetoreadthedata.FlashdrivesusesolidstatetechnologyandstoredatainasimilarwaytotheBIOSchip.TypesofbackingstorageTypesofbackingstorageThemediumiswhatthedataisactuallystoredon.Examplesofmediaincludefloppydisks,CD-ROMsandzipdisks.Floppydisksholdabout1.44MBo

6、fdata.Zipdisksstoreupto750MBofdata.CDsholdaround700MBofdata.Theharddiskofthecomputerstoresthesysteminformation,programsanddatathatthecomputeruseseveryday.ComputerserverswilluseRAIDsystemswithmanyharddrivestoprovidehugecapacityandsaferstorage.Thedrivescanbemirror

7、edsothatdatawrittentooneofthemisalsowrittentoothers,soifonedrivefails,theothersjusttakeover.RemovableharddrivesplugintotheUSBportandcanbeusedforbackuportransferofdatatoanothercomputer.Backingstorage–harddrivesFloppydisksusedtobeusedalot,buttheyareunreliableanddon

8、’tholdverymuchdata,sotheyarerarelyusednow.Theyhold1.44MBofdata,soareonlyreallyusefulforbackingupormovingsmallfilesthatdon’tcontaingraphics.Theyareeasilydamaged