硬盘结构及基本知识.ppt

ByPatiwatKamonpet,BasicDiscDrive,DiscDriveOverviewDiscDriveBasicsMagneticRecordingBasicsRecordingChannel,ComputerSystem,DiscDriveOverview,TodaysPCArchitecture,IOBusLogic,ISABus,Otherperipherals,CPUPentiumPro,Memory,PCIBridgeChip,VideoGraphicsAdapterCard,InterfaceAdapterCard,Monitor,IDEorSCSIDiscDrive,Cable,RibbonCable,PCIBoardEdgeConnection,PCIBoardEdgeConnection,PCIBus,LocalSystemBus,WiredonMotherBoard,WiredonMotherBoard,WiredonMotherBoard,Files,CollectionofBytesTextDocumentComputerInstructionsPictureetc.,SequenceofBlocks,Storedin,Fileisreferencedbyafilenameratherthanlocationondisk.Filesaremanagedbythecomputersoperatingsystem.Thediskdrivehasnoawarenessoffiles.,StoringFilesonDiscDrive,Computer,DiscDrive,Hereare3BlockofDataStartStoringinLocation5,Controller,InterfaceAdapter,File:Letter.DOC,LETTWR.DOC,ANOTHER.DOC,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,DIRECTORY,TransferRateinMegaMytespersecond(MBps),HowtoAccessFiles,Directory=AListofFilenamesandLacations,FilenameLETTER.DOCPROGRAM.EXEANOTHER.DOC.,Blocklocationondisk,5,6*,7*1024,1025*,1026*,1027*12,13*,14*,15*,16*.,Theoperatingsysteminthecomputerkeepstrackofthedirectory,*InDOS,thedirectorykeepstrackofthelocationforonlythe1stblockofeachfile.TheFileAllocationTable,orFAT,keepstrackofthelocationoftheotherblocks.,HDAComponents,DISC,CIRCULATEFILTER,CLAMPRING,ODLIMITSTOP,BOTTOMPOLE,VCM,PCC,PREAMPCHIP,IDLIMITSTOP,HEAD,FLEXURE,ARM,PIVOTCARTRIDGEBEARING,TOPVIEW,DiscDriveBasics,PCBComponents,HOSTCONTROLLER,VCM&SPINDLECONTROLLER,READ/WRITECHANNEL,MICROCONTROLLER,SERVOCONTROLLER,SRAM,DRAM,SHOCKSENSOR,SPINDLECONNECTOR,HDACONNECTOR,SHOCKIC,MassStorageArchitectureUsingDiscDrives,Read/WriteChannel,PositionSystem,SPMControl,SpindleMotor,VCM(VoiceCoilMotor),Controller,InterfaceAdapter,Memory,CPU,PC-ATSystemBus(ISA),SCSIRibbonCable,Embebbedonmotherboardoradd-incard,BlockDefinitions,UsingRecordingHeadToMagnetizeAFilm,FilmMotion,Current,Magnetized,NotMagnetized,N,S,WritingDataOnAMagneticFilm,FilmMotion,CurrentReversed,TransitionResults,S,N,Track,Track=AstripofdatawrittenonamagneticfilmEachbitsvalueissampledatregularinterval:1whenmagnetictransitionpresents0whenmagnetictransitiondoesnotpresent,TrackWidth,0,1,0,0,1,1,1,SamplingPeriod,WriteOtherTracksbyMovingtheHead,0,0,0,0,0,1,1,1,1,1,1,1,1,FilmMotion,TrackDensity,TrackWidth,TrackPitch,TrackDensity=Numberoftracksthatfitinoneinch(TPI),BitDensity(LinearDensity),BitLength,BitDensity=Numberofbitsthatfitinoneinchoftrack(BPI),ArialDensity,1”,1”,ArealDensity=Theamountofdatathatcanbestoredin1squareinch,AD=BPI*TPI,ReadingDataBackbyMRReadHead,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,0,0,0,RunconstantcurrentthroughMRstripe,Measuretheresistance.,Magneticfieldfromfilmpickedupbystripe,Fieldvariationinstripechangestheresistance,MRstandsforMagnetoResistance.,FilmMotion,ProblemwithMRStripe,TheMRstripedetectsthefieldfromatransitionalongwayaway.Solutions:SpacethetransitionsfarapartDetectseveraloverlappingbitsatatimeUseshields,ShieldedMRHead,ShieldspermitonlytheMRstripetoonlyseethemediabelowthegap.,TheVoltageBeingPickedUpisNotVeryHigh,Preamp,WallPlug220VoltsComputerSignals3-5VoltsFlashlightBattery1.5VoltsEKGwavesonyourskin0.01VoltsTVSignal(pickedupbyantenna)0.0008VoltsSignalFromRecordingHead0.0003Volts,0.0003V,0.075V,Pre-amplifythereadsignalveryclosetothehead,x250,InductiveWriteMRReadHead,IntegratedInductiveWriteMRReadHead,TrackWidth,ReaderGap,MagneticSpacing,HeadWidth,Trackwidthisdeterminedbyheadwidth(approximatelyequal).Bitlengthisdeterminedbyreadergapandspacingfromgaptomediaandmanyothers.,WhatControlsDensity?,TherateatwhichdataisreadorwrittenthroughtheheadmeasuredinMillionbitspersecond(Mbps),AsBitDensityIncreases,SoDoesDataRate!,Dontconfusedataratewithtransferrate,therateatwhichdatatransfersovertheinterface(inMegabytespersecondorMBps),FilmMotion,DataRate,MagneticStorageOnADiscDrive,CircularTracks,VoiceCoilMotormovestheheadinandout,SpindleMotordrivesthediscatconstantRPM,CalculateDataRate,r,0.9Hcof2000OeStrongenoughtomagnetizemedia,OutsidewritebubbleFieldHcof2000OeStrongenoughtomagnetizemedia,MediaLayerHc=2000Oe,WritingaTransition,?,?,?,?,?,Mediamotion,TransitionwrittenatthetrailingEdgefothewritebubble,Thisregionismagnetizedfirsttotheleftandthenagaintotheright,WritingaTransition,H,M,Mediamotion,Themediainthisareasees1200Oeinthenewdirection,Staysmagnetizedintheolddirection!,Themediainthisareasees2400Oeinthenewdirection,Beingmagnetizedintheolddirection!,Hc,M=0,RealTransitionsareBlurry!,H,M,Mediamotion,IttakesdistanceonthemediatochangethedirectionofmagnetizationThisiscalled“TransitionLength”,TransitionLength,TransitionLength,M,Hh,Hc,x,H,M,Hc,x,M,Previousstateofmedium,-50%,50%,Hd,transitionlength(2a),HorizontalComponentofHeadField,DemagnetizationFieldfromtheTransition,DemagnetizationFieldfromaTransition,M,Hd,a,transitionlengthparameter,x,Mr,Arecordedtransitiongeneratesdemagnetizationfield,Hd,Williams-ComstockModelofaRecordedTransition,M,Hd,H,Hc,x,H,M,Hc,DH,CalculatingTheTransitionLength,TypicalValues,FromWilliams-ComstockModel,WritingShorterSharperTransitions,Mediamotion,CloserHead-MediaSpacing(HMS)ThinnerMediaLayerShorterWriteGapLengthTighterMediaSwitchingFieldDistribution(allthemediaswitchatthesameH),WriteFieldGradient,MediaSquareness,HighWriteFieldGradient(closerbubbles),H,M,TransitionLength,HighMediaSquareness(howsteepM-Hcurve),ReadingwithaGMRReadHead,B,M,M,B,M,M,v,v,PhysicalMechanismofGMREffect,M,3d,Fermilevel,M,4s,Conductionband,Twocurrentmodel,FornormalGMRmaterials,s-dscatteringyieldsenergyloss:significantlycontributestoresistivity.,Thenumberofavailable3dstatesatFermisurfaceisdifferentfordifferentspins,PhysicalMechanismofGMREffect,Highresistancestate,Scatteringofspinelectronsoccurswithinamono-layerfromtheinterface.,ParallelState:,AntiparallelState,GMRReadHeadTransferCurve,M2,M1,M2,M1,q,Non-magneticconductivelayer,CharacterizingMagneticallyIsolatedPulses,d,T,2a,PW50,G,Where,TransitionParameter,Shield-to-ShieldSpacing,MagneticSeparation,MediaThickness,FromWilliams-Comstockmodel,AchievingDesirableIsolatedPulses,HighPeakAmplitudeIncreasefluxbyincreasingMr(RemanenceMagnetization)IncreasefluxbyincreasingmediathicknessDecreasemagneticspacingLongerreadgaplengthNarrowPulseWidthDecreasingmagneticspacingShortenreadgaplengthDecreasemediathicknessReduceself-demagbyincreasingcoercivityIncreasewriteheadfieldgradientinheadconstruction(dontusetoomuchcurrent),reading,writing,Needtrade-offs,RecordingChannel,RecordingChannel,Channelwritedata,Inputuserdata,ECCencoder,Channelencoder,Equalizer,Detector,ECCdecoder,Channeldecoder,outputuserdata,Analogreadbacksignal,10010110,110101101,1011011010,10010110,110101101,1011011010,DataWritingProcess,writecurrent,NRZI,clock,“Data”,magneticmedium,T,DataReadingProcess,SNSNSNSNSN,I,V,T,TheRead/WriteChannel,WriteCircuit,Preamp,Encoder,Decoder,ReadChannel,DataToRecord,WriteClock,DataReadBack,ReadRef.Clock,FromConroller,ToConroller,HDA,PCB,20mA,200Vpp,50mVpp,TTL,ECL,TTL,ECL,Pre-ampsWriteCircuit:H-BridgeDriver,Vcc,Rdamp,Head,Predriver,WriteData,WriteGate,Pre-ampsReadCircuit:DifferentialPre-amp,V,V,+-,Single-ended,Differential,Common-modenoiseisrejected!,Noise,TheReadChannel,SNSNSNSNSN,Objective,Outputadigitalpulsecorrespondingtothepeakofeachtransitiononthemedia,MEDIA,ReadSignal,DerivedClock,ReadChannelOutput,T,PeakDetector,ThresholdDetector,Differentiator,ZeroCrossingDetector,AND,Read-backpulse,1,0,1,Bitcell,Bitcell,Bitcell,DetectionWindow=T,NeedtimingRecoverycircuit,TimingRecovery:PhaseLockedLoop(PLL),FromPeakdetector,Clock,PeakDetectorOutput,VCOOutput,VCOveryveryearly,VCOveryearly,VCOearly,VCOslightlyearly,VCOOnTime,VCOslightlylate,VCOlate,PulseMissing,VCOOnTime,SlowDown,SlowDown,SlowDown,SlowDown,DontChange,SpeedUp,SpeedUp,DontChange,DontChange,PhaseDetectorOutput,Inter-SymbolInterference(ISI),LinearSuperpositionofpulsesReadbackWaveformWriteCurrent,Pulsesinterferewitheachotherwhenwrittenclosetogether:AmplitudesarereducedandTimingisdistortedUserDensity(UD)=PW50/T,T,PW50,PeakDetectorOutputExamples,PeakDetectionAnalogRead-backWaveformThresholdDetectorOutputDifferentiatedDataZeroCrossingDetectorOutputDetectedData,Read-backWaveformsatDifferentUserDensities,UD=0.75UD=1.5UD=2.0,AsynchronousDetection,PeakDetection,PLL,DetectorhasNOknowledgeofthebittiming,PLLknowsthebittimingNocommunicationtoDetector,SynchronousDetection,PeakDetection,PLL,Detectorhasknowledgeofwhenapulsemayoccur(bittiming)Canmakeahere/not-heredecisionMakesbetterdecisionsSignaltoNoiseRatio(SNR)canbelowerSampledDetectorallowsforpostcompensationModelandremoveISIasanerrorsource,SynchronousChannel:SampledPeakDetection,0.0-0.2-0.90.00.90.1-0.1-0.80.7-0.8-0.10.10.90-0.9-0.20.000-10100-11-10010-10000101001110010100,50%,-50%,DetectionThreshold,ReceivedSamples,Targetvalues,DetectedData,SynchronousChannel:SampledPeakDetection,50%,-50%,DetectionThreshold,-0.2-0.4-0.80.00.70.3-0.2-0.70.3-0.7-0.20.30.80-0.8-0.4-0.200-10100-10-10010-10000101001010010100,ReceivedSamples,Targetvalues,DetectedData,Missing1transitionOrhaveonetoomanytransitions,SequenceDetection,Weknowcertainsequencesshouldntexist.Makeuseofthefact!Step1:DeterminetheruleforwhichsequencesexistForsampledpeakdetection=polarityofpulsesmustalternateStep2:Comparetheobservedsampleswiththeexpectedsamplesfromallpossiblesequences.Choosetheclosestsequence.Closest=sequencewithminimumsquarederrorClosest=mostlikelysequenceMaximumLikelihood,Step1:RuleforPossibleSequences,Preconditioned,TheTrellis,EachpaththroughthetrelliscorrespondstoapossibledatasequenceEachpaththroughthetrellispredictsapossiblesequenceofsamplestoobserves,TrellisExample,PRML,PartialResponseMaximumLikelihoodBinarydatatransmissionmethodusedincommunicationssignalprocessingusedtodetectdatainanoisyenvironmentOriginallyusedwithdeepspaceprobesClass4appliedtomagneticrecordingchannels4inPR4referstotheclassofpartialresponsesystemusedformagneticrecordingchannelsTworelativelyindependentpartsPartialResponse-MethodforequalizingthereadbacksignaltoachieveasampledthreeleveloutputMaximumLikelihood-SequenceDetection,PartialResponse,Class4PartialResponseFilterorequalizeuntilatransitiongivesthefollowingwaveformTargetmorethanonenon-zerosampleperpulseEachsampleonlycontainspartofthepulse(response),2non-zerosamples(callthem+1),Allothersamples=0,PR4EqualizedIsolatedandDibitPulses,IsolatedPulse,DibitPulse,ExampleClass4PartialResponseWaveform,00100000110101110010111011,NRZI,PR4Eye-pattern,Allwaveformsatclockpointspassthroughoneofthreepointscorrespondingtosamplevaluesof-1,0,and1.Samplingonceeachbitperiodresultsinthreeleveloutput,TrellisDiagramforClass4PartialResponse,PR4StateDiagram,Read-backWaveformsatDifferentUserDensities,UD=0.75UD=1.5UD=2.0,MagneticChannelSpectrum,AtlowrecordingdensitiesthespectralenergyisconcentratednearonehalfofthechannelclockratefrequencyAthigherrecordingdensitiesmostofthesignalspectrumisbelowhalfofthechannelclockratefrequencyLimitchannelbandwidthto1/2Twithoutlosinginformation,WhygotohigherorderPartialResponses,PR4,PW50/T=0.5,EPR4,E2PR4,PRMLReadChannel,AGC-AutomaticGainControlmaintainsrequiredconstantsignallevel(VGA&GainControl)LowPassFilter-CoarseequalizationFIR-FiniteImpulseResponsefilterforfineequalizationADC-AnalogtoDigitalConvertersamplesequalizeroutputViterbiDetector-Comparesands