ByPatiwatKamonpetBasicDiscDriveDiscDriveOverviewDiscDriveBasicsMagneticRecordingBasicsRecordingChannelComputerSystemDiscDriveOverviewToday’sPCArchitectureIOBusLogicISABusOtherperipheralsCPUPentiumProMemoryPCIBridgeChipVideoGraphicsAdapterCardInterfaceAdapterCardMonitorIDEorSCSIDiscDriveCableRibbonCablePCIBoardEdgeConnectionPCIBoardEdgeConnectionPCIBusLocalSystemBusWiredonMotherBoardWiredonMotherBoardWiredonMotherBoardFilesCollectionofBytesTextDocumentComputerInstructionsPictureetc..SequenceofBlocksStoredinreferencedbyaratherthanlocationondisk.Filesaremanagedbythecomputer’soperatingsystem.. Thediskdrivehasnoawarenessoffiles.StoringFilesonDiscDrive

ComputerDiscDriveHereare3BlockofDataStartStoringinLocation5ControllerInterfaceAdapterFile:Letter.DOCLETTWR.DOCANOTHER.DOC01234567891011121314151617181920DIRECTORYTransferRateinMegaMytespersecond(MBps)HowtoAccessFilesDirectory=AListofandLacationsLETTER.DOCPROGRAM.EXEANOTHER.DOC...Blocklocationondisk5,6*,7*1024,1025*,1026*,1027*12,13*,14*,15*,16*...Theoperatingsysteminthecomputerkeepstrackofthedirectory*InDOS,thedirectorykeepstrackofthelocationforonlythe1stblockofeachfile.TheTable,orFAT,keepstrackofthelocationoftheotherblocks.HDAComponentsDISCCIRCULATEFILTERCLAMPRINGODLIMITSTOPBOTTOMPOLEVCMPCCPREAMPCHIPIDLIMITSTOPHEADFLEXUREARMPIVOTCARTRIDGEBEARINGTOPVIEWDiscDriveBasicsPCBComponentsHOSTCONTROLLERVCM&SPINDLECONTROLLERREAD/WRITECHANNELMICROCONTROLLERSERVOCONTROLLERSRAMDRAMSHOCKSENSORSPINDLECONNECTORHDACONNECTORSHOCKICMassStorageArchitectureUsingDiscDrivesRead/WriteChannelPositionSystemSPMControlSpindleMotorVCM(VoiceCoilMotor)ControllerInterfaceAdapterMemoryCPUPC-ATSystemBus(ISA)SCSIRibbonCableEmbebbedonmotherboardoradd-incardBlockDefinitionsREAD/WRITE DetectsbitsfromthesignalcomingfromtheCHANNEL

head(analog)andconvertsthemintodigitalbitsPOSITIONSYSTEM Seekstoandkeepstheheadspositionedover thecorrecttrackofdataonthedisk(E-Block- VCM-Servo)SPMCONTROL Keepsthediskrotatingandattheproper speedCONTROLLER RecognizesthedigitaldatacomingfromtheRead ChannelandorganizesitintoblocksofbytesUsingRecordingHeadToMagnetizeAFilmFilmMotionCurrentMagnetizedNotMagnetizedNSWritingDataOnAMagneticFilmFilmMotionCurrentReversedTransitionResultsSNTrackTrack=AstripofdatawrittenonamagneticfilmEachbit’svalueissampledatregularinterval: 1 whenmagnetictransitionpresents 0 whenmagnetictransitiondoesnotpresentTrackWidth0100111SamplingPeriodWriteOtherTracksbyMovingtheHead0000011111111FilmMotionTrackDensityTrackWidthTrackPitchTrackDensity=Numberoftracksthatfitinoneinch(TPI)BitDensity(LinearDensity)BitLengthBitDensity=Numberofbitsthatfitinoneinchoftrack(BPI)ArialDensity1”1”ArealDensity=Theamountofdatathatcanbestoredin1squareinchAD=BPI*TPIReadingDataBackbyMRReadHead0000011111111111000RunconstantcurrentthroughMRstripe,Measuretheresistance.MagneticfieldfromfilmpickedupbystripeFieldvariationinstripechangestheresistanceMRstandsforMagnetoResistance.FilmMotionProblemwithMRStripeTheMRstripedetectsthefieldfromatransitionalongwayaway.Solutions:SpacethetransitionsfarapartDetectseveraloverlappingbitsatatimeUseshieldsShieldedMRHeadShieldspermitonlytheMRstripetoonly‘see’themediabelowthegap.TheVoltageBeingPickedUpisNotVeryHighPreampWallPlug 220VoltsComputerSignals 3-5VoltsFlashlightBattery 1.5VoltsEKGwavesonyourskin 0.01VoltsTVSignal(pickedupbyantenna) 0.0008VoltsSignalFromRecordingHead 0.0003Volts0.0003V0.075VPre-amplifythereadsignalveryclosetotheheadx250InductiveWriteMRReadHeadIntegratedInductiveWriteMRReadHeadTrackWidthReaderGapMagneticSpacingHeadWidthTrackwidthisdeterminedbyheadwidth(approximatelyequal).Bitlengthisdeterminedbyreadergapandspacingfromgaptomedia andmanyothers.WhatControlsDensity?TherateatwhichdataisreadorwrittenthroughtheheadmeasuredinMillionbitspersecond(Mbps)AsBitDensityIncreases,SoDoesDataRate!Don’tconfusedataratewithtransferrate,therateatwhichdatatransfersovertheinterface(inMegabytespersecondorMBps)FilmMotionDataRateMagneticStorageOnADiscDriveCircularTracksVoiceCoilMotormovestheheadinandoutSpindleMotordrivesthediscatconstantRPMCalculateDataRater0.9<r<1.8for3.5”mediaDataRate=BitDensityxVelocity[bits/sec][bits/inch][inch/sec]DR=BPIx(RPM/60)x2πrCircumferenceatouteredge=2πr=11.3inchesVelocity=CircumferencexRotationRateVelocity=11.3inches/revx5400rpmx(1/60)min/secVelocity=1017inches/sec DataRate=180Kbpix1017inches/sec=183Mbps5400rpmBPI=180kSectors123456789101112131415161718190202122232425262728293031Diskdrivestoreover100,000bytesinatrack-->ToobigtodealwithWebreakeachtrackintochunkscalledsectors:MostcommonsectorSize=512Bytes(1024and2048bytescommon)TypicalSectorsPerTrack=50to256(determinedbybitdensity)Breakingtracksintosectorsusedupsomespace-FormattingEfficiency(5%-15%)ConstantAngularRecording(CAR)RidRodRadiusDataRateRidRodRadiusRidRodRadiusVelocityBPILessdataZoneBitRecordingRidRodRadiusBPIRidRodRadiusRidRodRadiusVelocityDataRateZoneMaximizeCapacityZoneZoneTableConstantAngularRecordingCapacityCapacity=numberoftracks?bitspertracknumberoftracks=TPI?(Rod–Rid)bitspertrack=BPI@Rid

?2πRidCaptacity=TPI?(Rod–Rid)?bitspertrackConstantAngularRecordingbitspertrack=constantRidRodRadiusbitspertrackAreaZoning–MaxCapacityZonedRecordingbitspertrack=2πr?BPIRidRodRadiusbitspertrackCapacityImprovement=(Rod–Rid)2?Rid≈50%for3.5”FFZoning–PracticalCapacityRidRodRadiusbitspertrackCapacityImprovement=(Rod–Rid)2?Rid?(1-N-1)N=numberofzones(4inthisexample)4zones→38%improvement8zones→44%improvement4zones→47%improvement4zones→48%improvementTypicalzoneddrivehas16zonesFor3.5”FFdrives,thelimittozoning’simprovementisabout150%MagnetizationCurveofMediaHHcDHMSquareness:Coercive-Squareness:Remanence:Saturationmagnetization:Coercivity:SlopeatCoercivity:MagneticRecordingBasicsLongitudinalRecordingWriteFieldHeadHeadHx=2000OeHx=2200OeLinesofconstanthorizontalfieldintensityGap180020002200240026002800TheWriteBubbleInsidewritebubbleField>Hcof2000OeStrongenoughtomagnetizemediaOutsidewritebubbleField<Hcof2000OeStrongenoughtomagnetizemediaHeadHeadGap200022002400260028001800MediaLayerHc=2000OeWritingaTransition??????????????????????????MediamotionTransitionwrittenatthetrailingEdgefothewritebubbleThisregionismagnetizedfirsttotheleftandthenagaintotherightWritingaTransition200022002400260028001800HMMediamotionThemediainthisareasees1200Oeinthenewdirection,Staysmagnetizedintheolddirection!Themediainthisareasees2400Oeinthenewdirection,Beingmagnetizedintheolddirection!HcM=0RealTransitionsareBlurry!200022002400260028001800HMMediamotionIttakesdistanceonthemediatochangethedirectionofmagnetizationThisiscalled“TransitionLength”TransitionLengthTransitionLengthMHhHcxHMHcxMPreviousstateofmedium-50%50%Hdtransitionlength(2a)HorizontalComponentofHeadFieldDemagnetizationFieldfromtheTransitionDemagnetizationFieldfromaTransitionMHdatransitionlengthparameterx+++MMHdHdTMrArecordedtransitiongeneratesdemagnetizationfieldHdWilliams-ComstockModelofaRecordedTransitionMHdHHcxHMHcDHCalculatingTheTransitionLengthwhereTransitionLengthParameter 500?MagneticSpacing 3μ”MediaThickness 200?WriteFieldGradientFactor(<0.75) 300Oe/μ”MediaCoercivity 2200OeRemanenceMagnetization 7500GCoerciveSquareness 80%TypicalValuesFromWilliams-ComstockModelWritingShorterSharperTransitionsMediamotionCloserHead-MediaSpacing(HMS)ThinnerMediaLayerShorterWriteGapLengthTighterMediaSwitchingFieldDistribution(allthemediaswitchatthesameH)WriteFieldGradientMediaSquarenessHighWriteFieldGradient(closerbubbles)200022002400260028001800HMTransitionLengthHighMediaSquareness(howsteepM-Hcurve)ReadingwithaGMRReadHeadBMMBMMvvPhysicalMechanismofGMREffectM3dFermilevelM4sConductionbandTwocurrentmodelFornormalGMRmaterialss-dscatteringyieldsenergyloss:significantlycontributestoresistivity.Thenumberofavailable3dstatesatFermisurfaceisdifferentfordifferentspinsPhysicalMechanismofGMREffectLowresistancestateMMMMHighresistancestateScatteringofspinelectronsoccurswithinamono-layerfromtheinterface.ParallelState:AntiparallelStateGMRReadHeadTransferCurveM2M1M2M1qNon-magneticconductivelayerCharacterizingMagneticallyIsolatedPulsesdT2aPW50GWhereTransitionParameterShield-to-ShieldSpacingMagneticSeparationMediaThicknessFromWilliams-ComstockmodelAchievingDesirableIsolatedPulsesHighPeakAmplitude IncreasefluxbyincreasingMr(RemanenceMagnetization) Increasefluxbyincreasingmediathickness Decreasemagneticspacing LongerreadgaplengthNarrowPulseWidth Decreasingmagneticspacing Shortenreadgaplength Decreasemediathickness Reduceself-demagbyincreasingcoercivity Increasewriteheadfieldgradientinheadconstruction (don’tusetoomuchcurrent)readingwritingNeedtrade-offsRecordingChannelRecordingChannelChannelwritedataInputuserdataECCencoderChannelencoderEqualizerDetectorECCdecoderChanneldecoderoutputuserdataAnalogreadbacksignal11010110110110110101101011011011011010DataWritingProcesswritecurrentNRZIclock“Data”magneticmediumTDataReadingProcessSNSNSNSNSNIVTTheRead/WriteChannelWriteCircuitPreampEncoderDecoderReadChannelDataToRecordWriteClockDataReadBackReadRef.ClockFromConrollerToConrollerHDAPCB20mA200μVpp50mVppTTL,ECLTTL,ECL1011101110111011Pre-amp’sWriteCircuit:H-BridgeDriverVccRdampHeadPredriverWriteDataWriteGatePre-amp’sReadCircuit:DifferentialPre-ampVV+-Single-endedDifferentialCommon-modenoiseisrejected!NoiseNoiseTheReadChannelSNSNSNSNSNObjectiveOutputadigitalpulsecorrespondingtothepeakofeachtransitiononthemediaMEDIAReadSignalDerivedClockReadChannelOutputTPeakDetectorThresholdDetectorDifferentiatorZeroCrossingDetectorANDRead-backpulse101BitcellBitcellBitcellDetectionWindow=TNeedtimingRecoverycircuitTimingRecovery:PhaseLockedLoop(PLL)PhaseDetectorIntegratorVCOFromPeakdetectorClockPeakDetectorOutputVCOOutputVCOveryveryearlyVCOveryearlyVCOearlyVCOslightlyearlyVCOOnTimeVCOslightlylateVCOlatePulseMissingVCOOnTimeSlowDownSlowDownSlowDownSlowDownDon’tChangeSpeedUpSpeedUpDon’tChangeDon’tChangePhaseDetectorOutputInter-SymbolInterference(ISI)LinearSuperpositionofpulsesReadbackWaveformWriteCurrent

Pulsesinterferewitheachotherwhenwrittenclosetogether: AmplitudesarereducedandTimingisdistortedUserDensity(UD)=PW50/TTPW50PeakDetectorOutputExamplesPeakDetectionAnalogRead-backWaveformThresholdDetectorOutputDifferentiatedDataZeroCrossingDetectorOutputDetectedDataRead-backWaveformsatDifferentUserDensitiesUD=0.75UD=1.5UD=2.0AsynchronousDetectionPeakDetectionPLLDetectorhasNOknowledgeofthebittimingPLLknowsthebittimingNocommunicationtoDetectorSynchronousDetectionPeakDetectionPLLDetectorhasknowledgeofwhenapulsemayoccur(bittiming) Canmakeahere/not-heredecision

Makesbetterdecisions SignaltoNoiseRatio(SNR)canbelowerSampledDetectorallowsforpostcompensation ModelandremoveISIasanerrorsourceSynchronousChannel:SampledPeakDetection0.0-0.2-0.90.00.90.1-0.1-0.80.7-0.8-0.10.10.90-0.9-0.20.000-10100-11-10010-1000010100111001010050%-50%DetectionThresholdReceivedSamplesTargetvaluesDetectedDataSynchronousChannel:SampledPeakDetection50%-50%DetectionThreshold-0.2-0.4-0.80.00.70.3-0.2-0.70.3-0.7-0.20.30.80-0.8-0.4-0.200-10100-10-10010-10000101001010010100ReceivedSamplesTargetvaluesDetectedDataMissing1transitionOrhaveonetoomanytransitionsSequenceDetectionWeknowcertainsequencesshouldn’texist.Makeuseofthefact!Step1: Determinetheruleforwhichsequencesexist Forsampledpeakdetection=polarityofpulsesmustalternateStep2: Comparetheobservedsampleswiththeexpectedsamples fromallpossiblesequences.Choosetheclosestsequence. Closest=sequencewithminimumsquarederror Closest=mostlikelysequence→MaximumLikelihoodStep1:RuleforPossibleSequencesPreconditionedTheTrellisEachpaththroughthetrelliscorrespondstoapossibledatasequenceEachpaththroughthetrellispredictsapossiblesequenceofsamplestoobservesTrellisExamplePRMLPartialResponseMaximum

LikelihoodBinarydatatransmissionmethodusedincommunicationssignalprocessingusedtodetectdatainanoisyenvironmentOriginallyusedwithdeepspaceprobesClass4appliedtomagneticrecordingchannels4inPR4referstotheclassofpartialresponsesystemusedformagneticrecordingchannelsTworelativelyindependentpartsPartialResponse-MethodforequalizingthereadbacksignaltoachieveasampledthreeleveloutputMaximumLikelihood-SequenceDetectionPartialResponseClass4PartialResponse FilterorequalizeuntilatransitiongivesthefollowingwaveformTargetmorethanonenon-zerosampleperpulse Eachsampleonlycontainspartofthepulse(response)2non-zerosamples(callthem+1)Allothersamples=0PR4EqualizedIsolatedandDibitPulsesIsolatedPulseDibitPulseExampleClass4PartialResponseWaveform00100000110101110010111011NRZIPR4Eye-patternAllwaveformsatclockpointspassthroughoneofthreepointscorrespondingto samplevaluesof-1,0,and1.SamplingonceeachbitperiodresultsinthreeleveloutputTrellisDiagramforClass4PartialResponsePR4StateDiagramRead-backWaveformsatDifferentUserDensitiesUD=0.75UD=1.5UD=2.0MagneticChannelSpectrumPW50/T=2PW50/T=3PW50/T=1PW50/T=1/2PW50/T=1/3Atlowrecordingdensitiesthespectralenergyisconcentratednearonehalfofthe channelclockratefrequencyAthigherrecordingdensitiesmostofthesignalspectrumisbelowhalfofthechannel clockratefrequencyLimitchannelbandwidthto1/2Twithoutlosinginforma