HDD from inside Main parts.docx
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HDD from inside Main parts.docx
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HDDfrominsideMainparts
HDDfrominside:
Mainparts
ThegoalofthisarticleistoshowyouhowamodernHardDiskDriveorHDDbuilt.Whatareitsmainparts,howdotheylookandwhatarethesepartsnamesandabbreviations.Asanexamplewearegoingtodisassemble3.5"SATAdrive.
Tomakeitmorefunwegoingtoteartopiecesprettynew1TBSeagateST31000333ASdrive.Let'stakealookonour"Guineapig".
ThefancypieceofgreenwovenglassandcopperwithSATAandpowerconnectorscalledPrintedCircuitBoardorPCB.PCBholdsonplaceandwireselectroniccomponentsofHDD.TheblackpaintedaluminumcasewithallstuffinsidecalledHeadandDiskAssemblyorHDA.ThecaseitselfcalledBase.
Nowlet'sremovePCBandseeelectroniccomponentsontheotherside.
TheheartofPCBisthebiggestchipinthemiddlecalledMicroControllerUnitorMCU.OnmodernHDDsMCUusuallyconsistsofCentralProcessorUnitorCPUwhichmakesallcalculationsandRead/Writechannel-specialunitwhichconvertsanalogsignalsfromheadsintodigitalinformationduringreadprocessandencodesdigitalinformationintoanalogsignalswhendriveneedstowrite.MCUalsohasIOportstocontroleverythingonPCBandtransmitdatathroughSATAinterface.
TheMemorychipisDDRSDRAMmemorytypechip.SizeofthememorydefinessizeofthecacheofHDD.ThisPCBhasSamsung32MBDDRmemorychipwhichtheoreticallymeansHDDhas32MBcache(andyoucanfindsuchinformationindatasheetonthisHDD)butit'snotquitetrue.Becausememorylogicallydividedonbufferorcachememoryandfirmwarememory.CPUeatssomememorytostoresomefirmwaremodulesandasfarasweknowonlyHitachi/IBMdrivesshowrealcachesizeindatasheetsfortheotherdrivesyoucanjustguesshowbigistherealcachesize.
NextchipisVoiceCoilMotorcontrollerorVCMcontroller.ThisfellowisthemostpowerconsumptionchiponPCB.Itcontrolsspindlemotorrotationandheadsmovements.ThecoreofVCMcontrollercanstandworkingtemperatureof100C/212F.
Flashchipstorespartofthedrive'sfirmware.Whenyouapplypoweronadrive,MCUchipreadscontentoftheflashchipintothememoryandstartsthecode.Withoutsuchcodedrivewouldn'tevenspinup.SometimesthereisnoflashchiponPCBthatmeanscontentoftheflashlocatedinsideMCU.
ShocksensorcandetectexcessiveshockappliedonadriveandsendsignaltoVCMcontroller.VCMcontrollerimmediatelyparksheadsandsometimesspinsdownthedrive.Ittheoreticallyshouldprotectthedriverfromfurtherdamagebutpracticallyitdoesn't,sodon'tdropyoudrive-itwouldn'tsurvive.OnsomedrivesshocksensorsusedfordetectionevenlightvibrationsandsignalsfromsuchsensorshelpVCMcontrollertuneupheadsmovements.Suchdrivesshouldhaveatleasttwoshocksensors.
AnotherprotectiondevicecalledTransientVoltageSuppressiondiodeorTVSdiode.ItprotectsPCBfrompowersurgesfromexternalpowersupply.WhenTVSdiodedetectspowersurgeitfriesitselfandcreatesshortcircuitbetweenpowerconnectorandground.TherearetwoTVSdiodesonthisPCBfor5Vand12Vprotection.
Let'stakeaquicklookonHDA
YoucanseemotorandheadscontactswhichwerehidingunderthePCB.ThereisalsosmallalmostunnoticeableholeonHDA.ThisholecalledBreathhole.YoumaybeheardoldrumorwhichsaysthatHDDhasvacuuminside,wellthatisnottrue.HDDusesBreathholetoequalizepressureinsideandoutsideHDA.FromtheinsideBreathholeclosedbyBreathfiltertomakeaircleananddry.
Nowitistimetotakealookunderthehood.Wearegoingtoremovethedrive'slid.
Theliditselfisnothinginteresting.Justapieceofsteelwithrubbercordfordustprotection.FinallywearegoingtoseeHDAfrominside.
Preciousinformationstoredonplatters,youcanseetopplatteronthepicture.Plattersmadeofpolishedaluminumorglassandcoveredwithseverallayersofdifferentcompoundsincludingferromagneticlayerwhichactuallystoresallthedata.AsyoucanseepartoftheplattercoveredwiththeDumper.DumperssometimescalledasSeparatorslocatedbetweenplatters,theyreduceairfluctuationsandacousticnoise.Usuallydumpersmadeofaluminumorplastic.AluminumdumpersbetterforcoolingairinsideHDA.
Nextpictureshowsplattersanddumpersfromtheside
HeadsmountedonHeadStackAssemblyorHSA.Thisdrivehasparkingareaclosertothespindleandifpowerisnotappliedonadrive,HSAnormallyparkedlikeonthepicture.
HDDisaprecisionmechanismandinordertoworkitrequiresverycleanairinside.DuringworkHDDmaycreatesomeverysmallparticlesofmetalandoilinside.TocleanairimmediatelyadriveusesRecirculationfilter.Thishi-techfilterpermanentlycollectsandabsorbsevenfinestparticles.Thefilterlocatedonthewayofairmotioncreatedbyplattersrotation.
Nowwearegoingtoremovetopmagnettoseewhatisunder.
HDDsuseverystrongNeodymiummagnets.Suchamagnetissostrongitcouldliftupto1300timesitsownweight,sodon'tputyourfingersbetweenmagnetandsteeloranothermagnet-itcandevelopgreatimpact.YoucanseeonthispicturethereisaHSAstopperonthemagnet.HSAstopperslimitHSAmovements,soheadswouldn'tbangontheplattersclampandontheothersidetheywouldn'tjustflyofftheplatters.HSAstoppersmayhavedifferentconstructionbuttherearealwaystwoofthemandtheyalwayspresentonmodernHDDs.OnthisdrivethesecondHSAstopperlocatedonHDAunderthetopmagnet.
Andhereiswhatyoumayseeunderthetopmagnet.
ThereistheotherHSAstopper.Andyoualsocanthesecondmagnet.TheVoicecoilisapartofHSA,VoicecoilandthemagnetsformVoiceCoilMotororVCM.VCMandHSAformtheActuator-adevicewhichmovestheheads.TrickyblackplasticthingycalledActuatorlatchisaprotectiondevice-itwillreleaseHSAwhendriveun-parking(loading)headsnormallyanditshouldblockHSAmovementsinthemomentofimpactifdrivewasdropped.Basicallyitprotects(should,atleast)headsfromunwantedmovementswhenHSAisinparkingarea.
OnthenextstepwegoingtotakeoutHSA
HSAhasprecisionbearingtomakemovementsniceandsmooth.ThebiggestpartofHSAmilledfrompieceofaluminumcalledtheArm.HeadsGimbalAssemblyorHGAattachedtotheArm.HGAsandArmsusuallyproducedondifferentfactories.FlexibleorangewidgetcalledFlexiblePrintedCircuitorFPCjoinsHSAandplatewithheadscontacts.
Let'stakecloserlookoneachpartofHSA.
VoicecoilconnectedtoFPC
Hereisthebearing
OnthenextpictureyoucanseeHSAcontacts
Thegasketmakesconnectionairtight.TheonlywayforairtogoinsideHDAisthroughthebreathinghole.Onthisdrivecontactscoveredwiththinlayerofgold,forbetterconductivity.
Thisistheclassicdefinitionofthearm.SometimesbythearmimplythewholemetalpieceofHSA.
TheblacksmallthingsattheendofHGAscalledSliders.Inmanysourcesyoucanfindthatslidersclaimedasactualheadsbutaslideritselfisnotaheadit'sawingwhichhelpsreadandwriteelementsflyundertheplatter'ssurface.HeadsflyingheightonmodernHDDsisabout5-10nanometers.Forexample:
anaveragehuman'shairisabout25000nanometersindiameter.Ifanyparticlegoesundertheslideritcouldimmediatelyoverheat(becauseoffriction)theheadsandkillthemthat'swhycleanairinsideHDAissoimportant.Theactualreadandwriteelementslocatedattheendofthesliderandtheyaresosmallthatcanonlybeseenunderagoodmicroscope.
Asyoucanseeslider'ssurfaceisnotflat,ithasaerodynamicalgrooves.Thesegrooveshelpasliderflyonthecertainheight.AirunderthesliderformsAirBearingSurfaceorABS.ABSmakessliderflyalmostparalleltotheplatter'ssurface.
Hereisanotherpictureoftheslider
Youcanclearlyseeheadscontacts.
ThereisveryimportantpartofHSAwhichwehaven'tdiscussedyet.Itcalledthepreamplifierorpreamp.Thepreampisachip,whichcontrolsheadsandamplifiessignalsfrom/tothem.
ThereasonwhythepreamplocatedinsideHDAissimple-signalsfromheadsareveryweakandonmodernHDDshavemorethan1GHzfrequency,iftakethepreampoutofHDAsuchweaksignalswouldn'tsurvive,theywilldisappearonthewaytoPCB.
Thepreamphasmuchmoretracksgoingtotheheads(rightside)thantotheHDA(leftside),it'sbecauseHDDcanworkonlywithone"head"(pairofreadanwriteelements)atatime.HDDsendscontrolsignalstothepreampandthepreampselectstheheadwhichHDDneedsatthecurrentmoment.ThisHDDhassixcontactsper"head",whysomany?
Onecontactisforground,othertwoforreadandwriteelements.Othertwoformicroactuators-specialpiezoelectricormagneticdeviceswhichcanmoveorrotateslider,ithelpstuneupheadspositionunderatrack.Andfinallythelastcontactisforaheater.Theheatercanhelpadjustheadsflyingheight.Theheatercanheatthegimbal-specialjointwhichconnectsslidertoHGA,thegimbalmadefromtwostripesofdifferentalloyswithdifferentthermalexpansion.Oncegimbalgotheateditbentsitselftowardplatter'ssurfaceandthisactionreducesflyingheight.Aftercoolingdownthegimbalstraightsitself.
Enoughaboutheads,let'scontinuedisassembling.Wegoingtoremovetopdumper.
That'showitlooks
AndnextpictureshowsHDAwithoutthetopdumperandHSA
Nowthetopplatterisnotcovered,youalsocanseethebottommagnet
Let'smovefurtherandremovetheplattersclamp
Theplattersclampsqueezingplattersintotheplatterspacket,sotheywouldn'tmove.
Platterssittingonthespindlehub,theplattersclampcreates
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