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1、Chapter5ComputerPeripheralsPeripheralsDevicesthatareseparatefromthebasiccomputerNottheCPU,memory,powersupplyClassifiedasinput,output,andstorageConnectviaPortsparallel,USB,serialInterfacetosystemsbusSCSI,IDE,PCMCIA2StorageDevicesPrimarymemoryExpandedstorageSec

2、ondarystorageDataandprogramsmustbecopiedtoprimarymemoryforCPUaccessPermanenceofdataDirectaccessstoragedevices(DASDs)OnlinestorageOfflinestorage–loadedwhenneeded3SpeedMeasuredbyaccesstimeanddatatransferrateAccesstime:averagetimeittakesacomputertolocatedataandre

3、aditmillisecond=one-thousandthofasecondDatatransferrate:amountofdatathatmovespersecond4HierarchyofStorage5SecondaryStorageDevicesHarddrives,floppydrivesCD-ROMandDVD-ROMdrivesCD-R,CD-RW,DVD-RAM,DVD-RWTapedrivesNetworkdrivesDirectaccessvs.SequentialaccessRotatio

4、nvs.Linear6MagneticDisksTrack–circleCylinder–sametrackonallplattersBlock–smallarcofatrackSector–pie-shapedpartofaplatterHead–readsdataoffthediskHeadcrashParkedheadsNumberofbitsoneachtrackisthesame!Densertowardsthecenter.CAV–constantangularvelocitySpinsthesames

5、peedforeverytrackHarddrives–3600rpm–7200rpmFloppydrives–360rpm7AHardDiskLayout8LocatingaBlockofDataAverageseektime:timerequiredtomovefromonetracktoanotherLatency:timerequiredfordisktorotatetobeginningofcorrectsectorTransfertime:timerequiredtotransferablockofda

6、tatothediskcontrollerbuffer9DiskAccessTimesAvg.SeektimeaveragetimetomovefromonetracktoanotherAvg.LatencytimeaveragetimetorotatetothebeginningofthesectorAvg.Latencytime=½*1/rotationalspeedTransfertime1/(#ofsectors*rotationalspeed)TotalTimetoaccessadiskblockAvg.

7、seektime+avg.latencytime+avg.transfertime10MagneticDisksDataBlockFormatInterblockgapHeaderDataFormattingdiskDiskInterleavingDiskArraysRAID–mirrored,stripedMajoritylogicfault-tolerantcomputersDiskInterleaving11DiskBlockFormatsSingleDataBlockHeaderforWindowsdis

8、k12AlternateDiskTechnologiesRemovableharddrivesDiskpack–diskplattersarestoredinaplasticcasethatisremovableAnotherversionincludesthediskheadandarmassemblyinthecaseFixed-headdiskdriv