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SystemStorage
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
Datacanbeheldin3non-volatileways
1. MagneticStorage2. Optical3. Flash
SystemStorage
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
Method1:Magnetic ThismethodusesMagnetic disksandareeitherfixedorremovable.ExamplesoffixedareHardDriveandremovableareFloppyDisks
Method2:OpticalDrivesThismethodsusesalasertoreadawritedata.ExamplesincludeCD/DVD
Method3:FlashMemoryThismethodusesFlashmemory.ExamplesincludeUSBthumbdrivesandSSDs
Non-VolatileStorage
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
Non-VolatilestoragedoesnotlosedatastoredonitwhenthepowerisremovedItsusuallycheapandslow
HardDiskDrives(HDD)
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
HardDrivesareaincrediblyefficientcomputermemorydevicethatusessimplemagnetismtostorevastamountsofinformation
HardDrivesusespinningmagneticdiskswhichthedata(1and0)isstoredon
Thisdataisreadandwrittenbyamechanicalarmswhichasthediskspinsmovesacrossthedisk
HardDiskDrives(HDD)
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
1.Actuatorthatmovestheread-writearm.Inolderharddrives,theactuatorsweresteppermotors.Inmostmodernharddrives,voicecoilsareusedinstead.Astheirnamesuggests,thesearesimpleelectromagnets,workingratherlike themovingcoils thatmakesoundsinloudspeakers.Theypositiontheread-writearmmorequickly,precisely,andreliably thansteppermotorsandarelesssensitive toproblemssuchastemperaturevariations.2.Read-writearmswingsread-writeheadbackandforthacrossplatter.3.Centralspindleallowsplattertorotateathighspeed.4.Magneticplatterstoresinformationinbinaryform.5.Plugconnectionslinkharddrivetocircuitboardinpersonalcomputer.6.Read-writeheadisatinymagnetontheendoftheread-writearm.7.Circuitboardonundersidecontrolstheflowofdatatoandfromtheplatter.8.Flexible connectorcarriesdatafromcircuitboardtoread-writeheadandplatter.9.Smallspindleallowsread-writearmtoswingacrossplatter.
HardDiskDrives(HDD)
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
Thedataisstoredinaveryorderlypatternoneachplatter.Bitsofdataarearrangedinconcentric,circularpathscalledtracks.Eachtrackisbrokenupintosmallerareascalledsectors.Partoftheharddrivestoresamapofsectorsthathavealreadybeenusedupandothersthatarestillfree.(InWindows, thismapiscalledtheFileAllocationTableorFAT.)Whenthecomputerwantstostorenewinformation,ittakesalookatthemaptofindsomefreesectors.Thenitinstructstheread- writeheadtomoveacrosstheplattertoexactlytherightlocationandstorethedatathere.Toreadinformation, thesameprocessruns inreverse.
FileSystems
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
• Formattinginstallsafilesystemontothepartition.•FileSystemsareamethodoforganizingyourfilesandfoldersontotheharddrive.•TheFilesystemtelltheoperatingsystemwhereitemsareheldsoitcanfindthem•Thinkofafilingcabinet.Filearearrangedinaspecificorderwithindicatortoeachsection.
HardDriveIssues
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
Diskfragmentationisaresultofhowacomputerusesstorageonaharddrive.Astimegoeson, filesonaharddiskdrivewillmostcertainlystarttofragment.Whenafileis'fragmented',partsofitarestoredatvariouslocationsonaharddiskdrive.Theendresultisthatinordertoaccessafile,acomputerneedstoaccessdifferentpartsofaharddiskdrive.Becauseofthemechanicalnatureofaharddiskdrive,theneedtoaccessdifferentpartscandramaticallyslowdowntheoverallperformance
AFragmentedHardDiskDriveshowing filesbeingSpreadallovertheHardDiskFile
HardDriveIssues
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
Thepicturetotheleftillustrateswhatafragmenteddiskwouldlooklikewhenfilesthatbelong togetheraresavedtodifferentareasoftheharddrive.Thepicturetotherightillustrateswhatadiskwouldlook likewhenthefilesthatbelong togetheraredefragmentedusingadefragmentingsoftwareapplication.
Afragmentedfiledoesnotloseanydata,norisitunreliableorinsecure.Inotherwords, fragmentationdoesnotcauseanyseriousproblems.Ontheotherhand,whenacomputeraccessesafragmentedfile, ittakeslonger thanaccessingonethatisnotfragmented.
HardDriveIssues
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
Whatproblemscouldamechanicalharddrivehave?•BadSectors- Aareaoftheharddiskdrivethatcannotholddatareliablybecauseofdamageorerror.Causedbybumping orbanging thedisk•LostCluster- Alostclusterisaclusterthattheoperatingsystemhasclassedasbeinginuse,butactuallycontainsnodata.- TheScanDiskutilitywithinWindowsisdesigned tosearchforlostclustersandmakethemavailabletothefilesystemagain.
Partitioning
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
Partitioning istheprocessofelectronicallysubdividing thephysicalharddriveintogroupsofcylinderscalledpartitions.Aharddrivemusthaveatleastonepartition, butmayhavemany.
Eachpartition isassignedadriveletter.i.e.C:orD:
Primary Partitions =Bootable(MustbesetActive).Extended Partitions =NonBootable(ContainLogicalDrives).
SolidStateDrive(SSD)
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
AnSSDdoesnothaveaDisktoreadandwritedata,itinsteadreliesonanembeddedprocessorcalledacontrollertoperformoperationsrelatedtoreadingandwritingdata.TheyareverysimilartoaUSBflashdrive.
RAID
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
RedundantArrayofIndependentDisks.
ASystemthatemploystwoormoredrivesincombinationforfaulttolerance,performanceorboth.
RAIDprovidesamethodofaccessingmultipleindividualdisksasifthearraywereonelargerdisk.
RAIDeitherspreadsorduplicatesthedataacrossmultipledisks,therebyeitherimprovingaccesstimeorreducingtheriskoflosingalldataifonedrivefails.
TypicallyRAIDisusedinlargefileservers,andapplicationservers,wheredataaccessibilityiscritical,andfaulttoleranceisrequired.
TherearenumberofdifferentRAIDlevels
BuyingaHardDiskDrive
Level3Unit2ComputerSystemsLecturer:AndrewBlundell
CapacityHowmuchdatatheHardDrivecanstore,usuallyinGigabytesorTerabytesCacheRandomAccessMemory (RAM) thatstorescopiesoffrequentlyuseddisksectorsinsotheycanbereadwithoutaccessingtheslowerdiskRead/WriteSpeedThereadspeedishowlong ittakestoreadsomething fromthedrive-- so,howlong ittakestoopenafilethat’sstoredonthedrive.Thewritespeedishowlong ittakestosavesomethingon tothedrive.InterfaceTheconnector theharddriveusestocommunicatewiththemotherboard usuallySATAorIDEFormFactorThesizeofthedisk.2.5"(smallfor laptops)or3.5“(DesktopSize)