硬盘结构及基本知识

85,Basic Servo,Click to edit Master title style,Product Performance Engineering,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,By Patiwat Kamonpet,Basic Disc Drive,Disc Drive Overview,Disc Drive Basics,Magnetic Recording Basics,Recording Channel,Computer System,Disc Drive Overview,Todays PC Architecture,IO Bus,Logic,ISA Bus,Other peripherals,CPU,Pentium Pro,Memory,PCI Bridge,Chip,Video Graphics,Adapter Card,Interface,Adapter Card,Monitor,IDE or SCSI,Disc Drive,Cable,Ribbon Cable,PCI Board Edge,Connection,PCI Board Edge,Connection,PCI Bus,Local System Bus,Wired on,Mother Board,Wired on,Mother Board,Wired on,Mother Board,Files,Collection of Bytes,Text,Document,Computer Instructions,Picture,etc.,Sequence of Blocks,Stored in,File 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.,Storing Files on Disc Drive,Computer,Disc Drive,Here are 3 Block of Data,Start Storing in Location 5,Controller,Interface,Adapter,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,Transfer Rate,in Mega Mytes per second,(MBps),How to Access Files,Directory = A List of Filenames and Lacations,Filename,LETTER.DOC,PROGRAM.EXE,ANOTHER.DOC,. . .,Block location on disk,5, 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.,HDA Components,DISC,CIRCULATE FILTER,CLAMP RING,OD LIMIT STOP,BOTTOM POLE,VCM,PCC,PREAMP CHIP,ID LIMIT STOP,HEAD,FLEXURE,ARM,PIVOT CARTRIDGE,BEARING,TOP VIEW,Disc Drive Basics,PCB Components,HOST CONTROLLER,VCM & SPINDLE,CONTROLLER,READ/WRITE CHANNEL,MICROCONTROLLER,SERVO CONTROLLER,SRAM,DRAM,SHOCK SENSOR,SPINDLE,CONNECTOR,HDA CONNECTOR,SHOCK IC,Mass Storage Architecture Using Disc Drives,Read/Write,Channel,Position,System,SPM,Control,Spindle Motor,VCM (Voice Coil Motor),Controller,Interface,Adapter,Memory,CPU,PC-AT System Bus (ISA),SCSI Ribbon Cable,Embebbed on mother board or add-in card,Block Definitions,READ/WRITE Detects bits from the signal coming from the,CHANNEL,head(analog) and converts them into digital bits,POSITION 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 bytes,Using Recording Head To Magnetize A Film,Film Motion,Current,Magnetized,Not Magnetized,N,S,Writing Data On A Magnetic Film,Film Motion,Current Reversed,Transition Results,S,N,Track,Track = A strip of data written on a magnetic film,Each bits value is sampled at regular interval:,1 when magnetic transition presents,0when magnetic transition does not present,Track Width,0,1,0,0,1,1,1,Sampling Period,Write Other Tracks by Moving the Head,0,0,0,0,0,1,1,1,1,1,1,1,1,Film Motion,Track Density,Track Width,Track Pitch,Track Density = Number of tracks that fit in one inch (TPI),Bit Density (Linear Density),Bit Length,Bit Density = Number of bits that fit in one inch of track (BPI),Arial Density,1”,1”,Areal Density = The amount of data that can be stored in 1 square inch,AD = BPI * TPI,Reading Data Back by MR Read Head,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,0,0,0,Run constant current through MR stripe, Measure the resistance.,Magnetic field from film,picked up by stripe,Field variation in stripe,changes the resistance,MR stands for MagnetoResistance.,Film Motion,Problem with MR Stripe,The 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 shields,Shielded MR Head,Shields permit only the MR stripe to only see the media below the gap.,The Voltage Being Picked Up is Not Very High,Preamp,Wall Plug220 Volts,Computer Signals3-5 Volts,Flashlight Battery1.5 Volts,EKG waves on your skin0.01 Volts,TV Signal (picked up by antenna)0.0008 Volts,Signal From Recording Head0.0003 Volts,0.0003V,0.075V,Pre-amplify the read signal,very close to the head,x250,Inductive Write MR Read Head,Integrated Inductive Write MR Read Head,Track Width,Reader Gap,Magnetic Spacing,Head Width,Track 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?,The rate at which data,is read or written,through the head,measured in Million bits,per second (Mbps),As Bit Density Increases,So Does Data Rate !,Dont confuse data rate with transfer rate, the rate at which,data transfers over the interface (in Megabytes per second,or MBps),Film Motion,Data Rate,Magnetic Storage On A Disc Drive,Circular Tracks,Voice Coil Motor moves,the head in and out,Spindle Motor drives the disc,at constant RPM,Calculate Data Rate,r,0.9 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%),Constant Angular Recording (CAR),R,id,R,od,Radius,Data Rate,R,id,R,od,Radius,R,id,R,od,Radius,Velocity,BPI,Less data,Zone Bit Recording,R,id,R,od,Radius,BPI,R,id,R,od,Radius,R,id,R,od,Radius,Velocity,Data Rate,Zone,Maximize Capacity,Zone,Zone Table,Constant Angular Recording Capacity,Capacity = number of tracks,bits per track,number of tracks = TPI,(R,od, R,id,),bits per track = BPI R,id,2,R,id,Captacity = TPI,(R,od, R,id,),bits per track,Constant Angular Recording,bits per track = constant,R,id,R,od,Radius,bits per track,Area,Zoning Max Capacity,Zoned Recording,bits per track = 2,r,BPI,R,id,R,od,Radius,bits per track,Capacity Improvement =,(R,od, R,id,),2,R,id, 50% for 3.5”FF,Zoning Practical Capacity,R,id,R,od,Radius,bits per track,Capacity Improvement =,(R,od, R,id,),2,R,id,(1-N,-1,),N = number of zones,(4 in this example),4 zones 38% improvement,8 zones 44% improvement,4 zones 47% improvement,4 zones 48% improvement,Typical zoned drive has 16 zones,For 3.5” FF drives, the limit to zonings improvement is about 150%,Magnetization Curve of Media,H,H,c,D,H,M,Squareness:,Coercive-Squareness:,Remanence:,Saturation magnetization:,Coercivity:,Slope at Coercivity:,Magnetic Recording Basics,Longitudinal Recording Write Field,Head,Head,H,x,= 2000Oe,H,x,= 2200Oe,Lines of constant,horizontal field,intensity,Gap,1800,2000,2200,2400,2600,2800,The Write Bubble,Inside write bubble,Field H,c,of 2000Oe,Strong enough to magnetize media,Outside write bubble,Field H,c,of 2000Oe,Strong enough to magnetize media,Head,Head,Gap,2000,2200,2400,2600,2800,1800,Media Layer,H,c,= 2000Oe,Writing a Transition,? ? ? ? ?,? ? ? ? ? ? ?,?,? ? ? ? ?,? ? ? ? ?,Media motion,Transition written at the trailing,Edge fo the write bubble,This region is magnetized first to the left,and then again to the right,Writing a Transition,2000,2200,2400,2600,2800,1800,H,M,Media motion,The media in this area sees,1200 Oe in the new direction,Stays magnetized in the old direction !,The media in this area sees,2400 Oe in the new direction,Being magnetized in the old direction !,H,c,M=0,Real Transitions are Blurry !,2000,2200,2400,2600,2800,1800,H,M,Media motion,It takes distance on the media,to change the direction of magnetization,This is called “Transition Length”,Transition Length,Transition Length,M,H,h,H,c,x,H,M,H,c,x,M,Previous state of medium,-50%,50%,H,d,transition length (2a),Horizontal Component,of Head Field,Demagnetization Field,from the Transition,Demagnetization Field from a Transition,M,H,d,a,transition length parameter,x,+,+,+,M,M,H,d,H,d,T,M,r,A recorded transition generates,demagnetization field,H,d,Williams-Comstock Model of a Recorded Transition,M,H,d,H,H,c,x,H,M,H,c,D,H,Calculating The Transition Length,where,Transition Length Parameter,500 ,Magnetic Spacing,3,”,Media Thickness,200 ,Write Field Gradient Factor (0.75),300 Oe/,”,Media Coercivity,2200 Oe,Remanence Magnetization,7500 G,Coercive Squareness,80%,Typical Values,From Williams-Comstock Model,Writing Shorter Sharper Transitions,Media motion,Closer Head-Media Spacing (HMS),Thinner Media Layer,Shorter Write Gap Length,Tighter Media Switching Field Distribution,(all the media switch at the same H),Write Field,Gradient,Media,Squareness,High Write Field Gradient (closer bubbles),2000,2200,2400,2600,2800,1800,H,M,Transition Length,High Media Squareness (how steep M-H curve),Reading with a GMR Read Head,B,M,M,B,M,M,v,v,Physical Mechanism of GMR Effect,M,3d,Fermi level,M,4s,Conduction band,Two current model,For normal GMR materials,s-d scattering yields energy loss: significantly contributes to resistivity.,The number of available 3d states at Fermi surface is different for different spins,Physical Mechanism of GMR Effect,Low resistance state,M,M,M,M,High resistance state,Scattering of spin electrons occurs within a mono-layer from the interface.,Parallel State:,Antiparallel State,GMR Read Head Transfer Curve,M,2,M,1,M,2,M,1,q,Non-magnetic,conductive layer,Characterizing Magnetically Isolated Pulses,d,T,2a,PW50,G,Where,Transition Parameter,Shield-to-Shield Spacing,Magnetic Separation,Media Thickness,From Williams-Comstock model,Achieving Desirable Isolated Pulses,High Peak Amplitude,Increase flux by increasing M,r,(Remanence Magnetization),Increase flux by increasing media thickness,Decrease magnetic spacing,Longer read gap length,Narrow Pulse Width,Decreasing magnetic spacing,Shorten read gap length,Decrease media thickness,Reduce self-demag by increasing coercivity,Increase write head field gradient in head construction,(dont use too much current),reading,writing,Need trade-offs,Recording Channel,Recording Channel,Channel write data,Input,user data,ECC encoder,Channel encoder,Equalizer,Detector,ECC decoder,Channel decoder,output,user data,Analog readback signal,10010110,110101101,1011011010,10010110,110101101,1011011010,Data Writing Process,write current,NRZI,clock,“Data”,magnetic medium,T,Data Reading Process,S N S N S N S N S N,I,V,T,The Read/Write Channel,Write,Circuit,Preamp,Encoder,Decoder,Read,Channel,Data To Record,Write Clock,Data Read Back,Read Ref.Clock,From,Conroller,To,Conroller,HDA,PCB,20 mA,200,V,pp,50 mV,pp,TTL, ECL,TTL, ECL,1,0,1,1,1,0,1,1,1,0,1,1,1,0,1,1,Pre-amps Write Circuit: H-Bridge Driver,V,cc,R,damp,Head,Predriver,Write Data,Write Gate,Pre-amps Read Circuit: Differential Pre-amp,V,V,+,-,Single-ended,Differential,Common-mode noise,is rejected !,Noise,Noise,The Read Channel,S N S N S N S N S N,Objective,Output a digital pulse corresponding to the peak of each transition on the media,MEDIA,Read,Signal,Derived,Clock,Read Channel,Output,T,Peak Detector,Threshold,Detector,Differentiator,Zero Crossing,Detector,AND,Read-back,pulse,1,0,1,Bitcell,Bitcell,Bitcell,Detection Window = T,Need timing,Recovery circuit,Timing Recovery: Phase Locked Loop (PLL),Phase,Detector,Integrator,VCO,From Peakdetector,Clock,Peak Detector,Output,VCO,Output,VCO,very very,early,VCO,very,early,VCO,early,VCO,slightly,early,VCO,On Time,VCO,slightly,late,VCO,late,Pulse,Missing,VCO,On Time,Slow,Down,Slow,Down,Slow,Down,Slow,Down,Dont,Change,Speed,Up,Speed,Up,Dont,Change,Dont,Change,Phase,Detector,Output,Inter-Symbol Interference (ISI),Linear Superposition of pulses,Readback,Waveform,Write Current,Pulses interfere with each other when written close together:,Amplitudes are reduced and Timing is distorted,User Density (UD) = PW50 / T,T,PW50,Peak Detector Output Examples,Peak Detection,Analog Read-back Waveform,Threshold Detector Output,Differentiated Data,Zero Crossing Detector Output,Detected Data,Read-back Waveforms at Different User Densities,UD = 0.75,UD= 1.5,UD = 2.0,Asynchronous Detection,Peak,Detection,PLL,Detector has,NO,knowledge,of the bit timing,PLL knows the bit timing,No communication to Detector,Synchronous Detection,Peak,Detection,PLL,Detector has knowledge of when a pulse may occur (bit timing),Can make a here / not-here decision,Makes better decisions,Signal to Noise Ratio (SNR) can be lower,Sampled Detector allows for post compensation,Model and remove ISI as an error source,Synchronous Channel: Sampled Peak Detection,0.0 -0.2 -0.9 0.0 0.9 0.1 -0.1 -0.8 0.7 -0.8 -0.1 0.1 0.9 0 -0.9 -0.2 0.0,0 0 -1 0 1 0 0 -1 1 -1 0 0 1 0 -1 0 0,0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 0 0,50%,-50%,Detection Threshold,Received,Samples,Target,values,Detected,Data,Synchronous Channel: Sampled Peak Detection,50%,-50%,Detection Threshold,-0.2 -0.4 -0.8 0.0 0.7 0.3 -0.2 -0.7 0.3 -0.7 -0.2 0.3 0.8 0 -0.8 -0.4 - 0.2,0 0 -1 0 1 0 0 -1 0 -1 0 0 1 0 -1 0 0,0 0 1 0 1 0 0 1 0 1 0 0 1 0 1 0 0,Received,Samples,Target,values,Detected,Data,Missing 1 transition,Or have one too,many transitions,Sequence Detection,We know certain sequences shouldnt exist.,Make use of the fact !,Step 1:Determine the rule for which sequences exist,For sampled peak detection = polarity of pulses must alternate,Step 2:Compare the observed samples with the expected samples,from,all possible sequences,. Choose the closest sequence.,Closest = sequence with minimum squared error,Closest = most likely sequence Maximum Likelihood,Step 1: Rule for Possible Sequences,Preconditioned,The Trellis,Each path through the trellis corresponds to a possible data sequence,Each path through the trellis predicts a possible sequence of samples to observes,Trellis Example,PRML,P,artial,R,esponse,M,aximum,L,ikelihood,Binary data transmission method used in communications signal processing used to detect data in a noisy environment,Originally used with deep space probes,Class 4 applied to magnetic recording channels,4 in PR4 refers to the class of partial response system used for magnetic recording channels,Two relatively independent parts,Partial Response - Method for equalizing the readback signal to achieve a sampled three level output,Maximum Likelihood - Sequence Detection,Partial Response,Class 4 Partial Response,Filter or equalize until a transition gives the following waveform,Target more than one non-zero sample per pulse,Each sample only contains part of the pulse (response),2 non-zero samples,(call them +1),All other samples = 0,PR4 Equalized Isolated and Dibit Pulses,Isolated Pulse,Dibit Pulse,Example Class 4 Partial Response Waveform,0 0 1 0 0 0 0 0 1 1 0 1 0 1 1 1 0 0 1 0 1 1 1 0 1 1,NRZI,PR4 Eye-pattern,All waveforms at clock points pass through one of three points corresponding to sample values of -1, 0, and 1.,Sampling once each bit period results in three level output,Trellis Diagram for Class 4 Partial Response,PR4 State Diagram,Read-back Waveforms at Different User Densities,UD = 0.75,UD= 1.5,UD = 2.0,Magnetic Channel Spectrum,PW50/T=2,PW50/T=3,PW50/T=1,PW50/T=1/2,PW50/T=1/3,At low recording densities the spectral energy is concentrated near one half of the channel clock rate frequency,At higher recording densities most of the signal spectrum is below half of the channel clock rate frequency,Limit channel bandwidth to 1/2T without losing information,Why go to higher order Partial Responses,PR4,PW50/T=0.5,EPR4,E2PR4,PRML Read Channel,AGC - Automatic Gain Control maintains required constant signal level (VGA & Gain Control),Low Pass Filter - Coarse equalization,FIR - Finite Impulse Response filter for fine equalization,ADC - Analog to Digital Converter samples equalizer output,Viterbi Detector - Compares and selects maximum likelihood sequence,PRML Write Channel,Randomizer - Reduces probability of occurrence of worst case repeated patterns that are detrimental to the timing and gain loops,Encoder - Encodes user data into channel data,Precoder - Limits error propagation, Compensates for response of the equalized channel,Write Precomp - Write precompensation for nonlinear effects (not for ISI),Write Precompensation,Compensate for nonlinear effects - demagnetization field from previously written transition shifts transition early,M,H,d,H,H,c,x,RLL Coding,Run Length Limited Codes (RLL) defined as (d, G/I),d = Minimum number of 0s separating 1s,G = Maximum number of 0s separating 1s in global output,I = Maximum number of 0s separating 1s in each interleave,d controls intersymbol interference,Codes for PRML channels d = 0,ISI is constructively used and not a problem as in peak detection,G influences timing and gain correction update rates and sets lowest frequency of channel which must not be distorted by filter,I influences the Viterbi path memory by minimizing the number of states between crossovers,Code Rate,Code Rate - number of recorded bits written on disc for each user bit to be recorded,CodeRate,1,72/3,0,4/48/9,0,6/616/17,Lower rate codes require higher frequency clocks,Higher rate codes result in lower frequencies which requires a lower filter bandwidth that filters out more noise,Higher rate codes are more complex,User Density = Channel Density * Rate,