硬盘结构及基本知识.ppt

1、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 Adapte

2、r 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

3、 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 : L

4、etter. 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, 10

5、25*, 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,

6、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

7、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,

8、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 tran

9、sition 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 Densi

10、ty),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, Me

11、asure 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

12、 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 Sig

13、nal (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 he

14、ad 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 confus

15、e 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,

16、0.9 r 1.8 for 3.5” media,Data Rate = Bit Density x Velocity bits/sec bits/inch inch/sec,DR = BPI x (RPM/60) x 2r,Circumference at outer edge = 2r = 11.3 inches Velocity = Circumference x Rotation Rate Velocity = 11.3 inches/rev x 5400 rpm x (1/60) min/sec Velocity = 1017 inches/sec Data Rate = 180 K

17、bpi x 1017 inches/sec = 183 Mbps,5400 rpm BPI = 180k,Sectors,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,0,20,21,22,23,24,25,26,27,28,29,30,31,Disk drive store over 100,000 bytes in a track - Too big to deal with We break each track into chunks called sectors :,Most common sector Size = 512 Byte

18、s (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),Zone Bit Recording,BPI,Velocity,Data Rate,Zone,Maximize Capacity,Zone,Zone Table,Consta

19、nt Angular Recording Capacity,Capacity = number of tracks bits per track number of tracks = TPI (Rod Rid) bits per track = BPI Rid 2Rid Captacity = TPI (Rod Rid) bits per track,Constant Angular Recording bits per track = constant,Rid,Rod,Radius,bits per track,Area,Zoning Max Capacity,Zoned Recording

20、 bits per track = 2r BPI, 50% for 3.5”FF,Zoning Practical Capacity,Rid,Rod,Radius,bits per track, (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 l

21、imit to zonings improvement is about 150%,Magnetization Curve of Media,Squareness:,Coercive-Squareness:,Remanence:,Saturation magnetization:,Coercivity:,Slope at Coercivity:,Magnetic Recording Basics,Longitudinal Recording Write Field,Head,Head,Hx = 2000Oe,Hx = 2200Oe,Lines of constant horizontal fi

22、eld intensity,Gap,1800,2000,2200,2400,2600,2800,The Write Bubble,Inside write bubble Field Hc of 2000Oe Strong enough to magnetize media,Outside write bubble Field Hc of 2000Oe Strong enough to magnetize media,Media Layer Hc = 2000Oe,Writing a Transition,? ? ? ? ?,? ? ? ? ? ? ?,?,? ? ? ? ?,? ? ? ? ?

23、,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,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

24、area sees 2400 Oe in the new direction, Being magnetized in the old direction !,Hc,M=0,Real Transitions are Blurry !,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,Hh,Hc,x,H,M,Hc,x,M,Pr

25、evious state of medium,-50%,50%,Hd,transition length (2a),Horizontal Component of Head Field,Demagnetization Field from the Transition,Demagnetization Field from a Transition,M,Hd,a,transition length parameter,x,Mr,A recorded transition generates demagnetization field,Hd,Williams-Comstock Model of a

26、 Recorded Transition,M,Hd,H,Hc,x,H,M,Hc,DH,Calculating The Transition Length,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 m

27、edia switch at the same H),Write Field Gradient,Media Squareness,High Write Field Gradient (closer bubbles),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 curren

28、t 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,High resistance state,Scattering of spin electrons occurs within a mono-l

29、ayer from the interface.,Parallel State:,Antiparallel State,GMR Read Head Transfer Curve,M2,M1,M2,M1,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-Comstoc

30、k model,Achieving Desirable Isolated Pulses,High Peak Amplitude Increase flux by increasing Mr (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

31、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,C

32、hannel 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 Ch

33、annel,Data To Record,Write Clock,Data Read Back,Read Ref.Clock,From Conroller,To Conroller,HDA,PCB,20 mA,200 Vpp,50 mVpp,TTL, ECL,TTL, ECL,Pre-amps Write Circuit: H-Bridge Driver,Vcc,Rdamp,Head,Predriver,Write Data,Write Gate,Pre-amps Read Circuit: Differential Pre-amp,V,V,+ -,Single-ended,Different

34、ial,Common-mode noise is rejected !,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,R

35、ead-back pulse,1,0,1,Bitcell,Bitcell,Bitcell,Detection Window = T,Need timing Recovery circuit,Timing Recovery: Phase Locked Loop (PLL),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

36、 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: Amplit

37、udes 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=

38、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 be

39、tter 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

40、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

41、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

42、 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 Tre

43、llis,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,Partial Response Maximum Likelihood Binary data transmission method used in communications signal processing used to detec

44、t 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 sign

45、al 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-

46、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 corre

47、sponding 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,At low recording densities the sp

48、ectral 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 equaliza