硬盘结构及基本知识.ppt
1Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringBy Patiwat KamonpetBasic Disc DriveDisc Drive OverviewDisc Drive BasicsMagnetic Recording BasicsRecording Channel2Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringComputer SystemDisc Drive Overview3Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringTodays PC ArchitectureIO BusLogicISA BusOther peripheralsCPUPentium ProMemoryPCI BridgeChipVideo GraphicsAdapter CardInterfaceAdapter CardMonitorIDE or SCSIDisc DriveCableRibbon CablePCI Board EdgeConnectionPCI Board EdgeConnectionPCI BusLocal System BusWired onMother BoardWired onMother BoardWired onMother Board4Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringFilesCollection of BytesTextDocumentComputer InstructionsPictureetc.Sequence of BlocksStored inFile is referenced by a filename rather than location on disk.Files are managed by the computers operating system.The disk drive has no awareness of files.5Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringStoring Files on Disc Drive ComputerDisc DriveHere are 3 Block of DataStart Storing in Location 5ControllerInterfaceAdapterFile:Letter.DOCLETTWR.DOCANOTHER.DOC01234567891011121314151617181920DIRECTORYTransfer Ratein Mega Mytes per second(MBps)6Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringHow to Access FilesDirectory=A List of Filenames and LacationsFilenameLETTER.DOC PROGRAM.EXE ANOTHER.DOC.Block location on disk5,6*,7*1024,1025*,1026*,1027*12,13*,14*,15*,16*.The operating system in the computer keeps track of the directory*In DOS,the directory keeps track of the location for only the 1st block of each file.The File Allocation Table,or FAT,keeps track of the location of the other blocks.7Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringHDA ComponentsDISCCIRCULATE FILTERCLAMP RINGOD LIMIT STOPBOTTOM POLEVCMPCCPREAMP CHIPID LIMIT STOPHEADFLEXUREARMPIVOT CARTRIDGEBEARINGTOP VIEWDisc Drive Basics8Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringPCB ComponentsHOST CONTROLLERVCM&SPINDLE CONTROLLERREAD/WRITE CHANNELMICROCONTROLLERSERVO CONTROLLERSRAMDRAMSHOCK SENSORSPINDLE CONNECTORHDA CONNECTORSHOCK IC9Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringMass Storage Architecture Using Disc DrivesRead/WriteChannelPositionSystemSPMControlSpindle Spindle MotorMotorVCM (Voice VCM (Voice Coil Motor)Coil Motor)ControllerInterfaceAdapterMemoryCPUPC-AT System PC-AT System Bus(ISA)Bus(ISA)SCSI Ribbon SCSI Ribbon CableCableEmbebbed on mother board or add-in card10Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringBlock DefinitionsREAD/WRITE Detects bits from the signal coming from the CHANNEL head(analog)and converts them into digital bitsPOSITION SYSTEMSeeks to and keeps the heads positioned over the correct track of data on the disk(E-Block-VCM-Servo)SPM CONTROL Keeps the disk rotating and at the proper speed CONTROLLERRecognizes the digital data coming from the Read Channel and organizes it into blocks of bytes11Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringUsing Recording Head To Magnetize A FilmFilm MotionCurrent12Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringWriting Data On A Magnetic FilmFilm MotionCurrent ReversedTransition Results13Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringTrackTrack=A strip of data written on a magnetic filmEach bits value is sampled at regular interval:1 when magnetic transition presents0when magnetic transition does not presentTrack WidthSampling Period14Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringWrite Other Tracks by Moving the HeadFilm Motion15Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringTrack DensityTrack WidthTrack PitchTrack Density =Number of tracks that fit in one inch(TPI)16Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringBit Density(Linear Density)Bit LengthBit Density =Number of bits that fit in one inch of track(BPI)17Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringArial Density1”1”Areal Density=The amount of data that can be stored in 1 square inchAD =BPI*TPI18Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringReading Data Back by MR Read HeadRun constant current through MR stripe,Measure the resistance.Magnetic field from filmpicked up by stripeField variation in stripechanges the resistanceMR stands for MagnetoResistance.Film Motion19Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringProblem with MR StripeThe MR stripe detects the field from a transition a long way away.Solutions:Space the transitions far apart Detect several overlapping bits at a time Use shields20Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringShielded MR HeadShields permit only the MR stripe to only see the media below the gap.21Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringThe Voltage Being Picked Up is Not Very HighWall Plug220 VoltsComputer Signals3-5 VoltsFlashlight Battery1.5 VoltsEKG waves on your skin0.01 VoltsTV Signal(picked up by antenna)0.0008 VoltsSignal From Recording Head0.0003 Volts0.0003V0.075VPre-amplify the read signal very close to the head22Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringInductive Write MR Read HeadIntegrated Inductive Write MR Read Head23Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringTrack WidthReader GapMagnetic SpacingHead WidthTrack width is determined by head width(approximately equal).Bit length is determined by reader gap and spacing from gap to media and many others.What Controls Density?24Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringThe rate at which data is read or written through the headmeasured in Million bits per second(Mbps)As Bit Density Increases,So Does Data Rate!Dont confuse data rate with transfer rate,the rate at whichdata transfers over the interface(in Megabytes per secondor MBps)Film MotionData Rate25Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringMagnetic Storage On A Disc DriveCircular TracksVoice Coil Motor movesthe head in and outSpindle Motor drives the discat constant RPM26Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringCalculate Data Rate0.9 r Too big to deal with We break each track into chunks called sectors:Most common sector Size =512 Bytes(1024 and 2048 bytes common)Typical Sectors Per Track =50 to 256 (determined by bit density)Breaking tracks into sectors used up some space-Formatting Efficiency(5%-15%)28Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringConstant Angular Recording(CAR)RidRodRadiusData RateRidRodRadiusRidRodRadiusVelocityBPILess data29Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringZone Bit RecordingRidRodRadiusBPIRidRodRadiusRidRodRadiusVelocityData RateZoneMaximize CapacityZone30Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringZone Table31Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringConstant Angular Recording CapacityCapacity=number of tracks bits per tracknumber of tracks=TPI (Rod Rid)bits per track=BPI Rid 2RidCaptacity=TPI (Rod Rid)bits per trackConstant Angular Recordingbits per track=constantRidRodRadiusbits per trackArea32Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringZoning Max CapacityZoned Recordingbits per track=2r BPIRidRodRadiusbits per trackCapacity Improvement=(Rod Rid)2 Rid 50%for 3.5”FF33Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringZoning Practical CapacityRidRodRadiusbits per trackCapacity Improvement=(Rod Rid)2 Rid(1-N-1)N=number of zones(4 in this example)4 zones 38%improvement8 zones 44%improvement4 zones 47%improvement4 zones 48%improvement Typical zoned drive has 16 zonesFor 3.5”FF drives,the limit to zonings improvement is about 150%34Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringMagnetization Curve of MediaHHcDHM Squareness:Coercive-Squareness:Remanence:Saturation magnetization:Coercivity:Slope at Coercivity:Magnetic Recording Basics35Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringLongitudinal Recording Write FieldHeadHeadHx=2000OeHx=2200OeLines of constanthorizontal fieldintensityGap18002000220024002600280036Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringThe Write BubbleInside write bubbleField Hc of 2000OeStrong enough to magnetize mediaOutside write bubbleField Hc of 2000OeStrong enough to magnetize mediaHeadHeadGap200022002400260028001800Media LayerHc=2000Oe37Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringWriting a Transition?Media motionTransition written at the trailingEdge fo the write bubbleThis region is magnetized first to the leftand then again to the right38Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringWriting a Transition200022002400260028001800HM Media motionThe media in this area sees1200 Oe in the new direction,Stays magnetized in the old direction!The media in this area sees2400 Oe in the new direction,Being magnetized in the old direction!HcM=039Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringReal Transitions are Blurry!200022002400260028001800HM Media motionIt takes distance on the mediato change the direction of magnetizationThis is called“Transition Length”Transition Length40Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringTransition LengthMHhHcxHMHcxMPrevious state of medium-50%50%Hdtransition length(2a)Horizontal Component of Head FieldDemagnetization Field from the Transition41Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringDemagnetization Field from a TransitionMHdatransition length parameterx+MMHdHdTMrA recorded transition generates demagnetization fieldHd42Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringWilliams-Comstock Model of a Recorded TransitionMHdHHcxHMHcDH43Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringCalculating The Transition LengthwhereTransition Length Parameter500 Magnetic Spacing3”Media Thickness200 Write Field Gradient Factor(0.75)300 Oe/”Media Coercivity2200 OeRemanence Magnetization7500 GCoercive Squareness80%Typical ValuesFrom Williams-Comstock Model44Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringWriting Shorter Sharper TransitionsMedia motionCloser Head-Media Spacing(HMS)Thinner Media LayerShorter Write Gap LengthTighter Media Switching Field Distribution(all the media switch at the same H)Write FieldGradientMediaSquarenessHigh Write Field Gradient(closer bubbles)200022002400260028001800HMTransition LengthHigh Media Squareness(how steep M-H curve)45Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringReading with a GMR Read HeadBMMBMMvv46Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringPhysical Mechanism of GMR EffectM3dFermi levelM4sConduction bandTwo current modelFor normal GMR materialss-d scattering yields energy loss:significantly contributes to resistivity.The number of available 3d states at Fermi surface is different for different spins 47Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringPhysical Mechanism of GMR EffectLow resistance stateMMMMHigh resistance stateScattering of spin electrons occurs within a mono-layer from the interface.Parallel State:Antiparallel State48Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringGMR Read Head Transfer CurveM2M1M2M1q qNon-magneticconductive layer49Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringCharacterizing Magnetically Isolated PulsesdT2aPW50GWhereTransition ParameterShield-to-Shield SpacingMagnetic SeparationMedia ThicknessFrom Williams-Comstock model50Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringAchieving Desirable Isolated PulsesHigh Peak AmplitudeIncrease flux by increasing Mr(Remanence Magnetization)Increase flux by increasing media thicknessDecrease magnetic spacingLonger read gap lengthNarrow Pulse WidthDecreasing magnetic spacingShorten read gap lengthDecrease media thicknessReduce self-demag by increasing coercivityIncrease write head field gradient in head construction(dont use too much current)readingwritingNeed trade-offs51Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringRecording Channel52Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringRecording ChannelChannel write dataInputuser dataECC encoderChannel encoderEqualizerDetectorECC decoderChannel decoderoutputuser dataAnalog readback signal10010110110101101101101101010010110110101101101101101053Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringData Writing Processwrite current NRZIclock“Data”magnetic mediumT54Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringData Reading Process S N S N S N S N S N IVT55Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringThe Read/Write ChannelWriteCircuitPreampEncoderDecoderReadChannelData To RecordWrite ClockData Read BackRead Ref.ClockFromConrollerToConrollerHDAPCB20 mA200 Vpp50 mVppTTL,ECLTTL,ECL101110111011101156Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringPre-amps Write Circuit:H-Bridge DriverVccRdampHeadPredriverWrite DataWrite Gate57Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringPre-amps Read Circuit:Differential Pre-ampVV+-Single-endedDifferentialCommon-mode noiseis rejected!NoiseNoise58Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringThe Read Channel S N S N S N S N S N ObjectiveOutput a digital pulse corresponding to the peak of each transition on the mediaMEDIAReadSignalDerivedClockRead ChannelOutputT59Basic ServoBasic ServoProduct Performance EngineeringProduct Performance EngineeringPeak DetectorThresholdDetectorDifferentiatorZero CrossingDetectorANDRead-backpulse101BitcellBitcellBitcellDetection Window=TNeed timingRecovery circuit60Bas
