Introduction
Themostcommonmemoryinearlycomputerswasmadeofvariousmagneticcores.Thiskindofmagneticcorememoryhasbeenreplacedbysemiconductormemoryonaminiatureintegratedcircuitblock.MagneticcorememorywasinventedbyWangAnofChineseoriginin1948(Note).Theoriginalmagneticcorememoryonlyhadacapacityofafewhundredbytes.
Magneettisen ydinmuistin ydinosa (2 kuvaa)
TheEnglishnameofthemagneticcoreiscore,andthemagneticcorememoryiscalledcorememory.Nowadays,althoughmagneticcorememoryhasbeeneliminated,somepeoplestillcallmemorycoreoutofhabit.Awireisinsertedintotheferritemagneticring.Whencurrentflowsindifferentdirectionsinthewire,themagneticringcanbemagnetizedintwodifferentdirections,andtheinformationrepresenting"1"or"0"isintheformofamagneticfield.Saveit.
Principle
Themagneticcorewillbemagnetizedorchangethedirectionofmagnetizationwhenacertaincurrentflowsonthewire.Thiscurrentthatcanmagnetizethemagneticcorecanbeobtainedinadvancethroughexperimentsandmaterialprocesscontrol.Theminimumthreshold.EachmagneticcorehastwoXYlinesperpendiculartoeachother,andthereisalsoadiagonalreadoutline.Theselinescanbeclearlyseenintheabovephoto.Theselinesformanarray,andXYaremadetwoseparately.Addressingindifferentdirections.Themagneticcorecanproducetwooppositedirectionsofmagnetizationaccordingtothedirectionofthecurrentduringmagnetization,whichcanbeusedasastateof0and1torecorddata.
Whenwriting,inputacurrentslightlyhigherthanthe50%magneticringmagnetizationthresholdontheXYcoordinatelinecorrespondingtothemagneticcoretobewritten,soonlythemagneticcorecorrespondingtotheXYcoordinateTherewillbecurrentsinbothlinesatthesametime.Aftersuperimposition,thecurrentwillexceedthethreshold.Themagneticcorewillbemagnetizedorchangethedirectionofmagnetizationtowriteonebitofdata.Thecurrentflowinginallothercoresiseither0orThe50%magnetizationthresholdcannotreachthemagnetizationcurrentandcannotbemagnetized,sonodataiswritten.
Itismorecomplicatedtoreadout.ThereadcurrentissenttoXYrespectively.Thesizeofthereadcurrentisslightlylargerthanthe50%magnetizationthresholdcurrentwhenitiswritten.ThedirectionofthereadcurrentisItisknowninadvance,sothattherewillbeacurrentexceedingthethresholdinthemagneticcorecorrespondingtotheXYaddressingcoordinates.Ifitsoriginalmagneticfielddirectionisoppositetothemagneticfielddirectioncorrespondingtothereadcurrent,thenduetothemagneticcoreThestateisreversed,thereisahugemagneticfluxchange,andtherewillbealargeinducedcurrentonthereadoutlinethattraversesobliquely,soweknowthatthismagneticcorestoresdatathatistheoppositeofthereadoutsignal.Ifitsoriginalmagneticfielddirectionisthesameasthedirectionofthemagneticfieldcorrespondingtothereadcurrent,thensincethemagneticstateofthemagneticcorehasnotchanged,therewillbenoinducedcurrentonthereadoutlinethatcrossesdiagonally,soweknowthismagneticfield.Thecorestoresthesamedataasthereadsignal.Thedatainthemagneticcoreisreadinthisway,butthisisnotfinishedyet,becauseitisworthnotingthatafterreadingthedataatthistime,obviouslynomatterwhatdataisstoredonthemagneticcore,itwillbewrittentothesameafterreading.Thedataisread,thatis,thereadisdestructive,sotheremustbeawaytorestorethestoreddataaftertheread.Therefore,afterreadingit,youneedtowritetheoriginaldataagainimmediatelytorestoretheoriginaldata.Themethodistheaforementionedmethodofwritingdata,usingthedataoriginallystoredinthemagneticringinthecachetowriteback.Therefore,thereadingofmagneticcorememoryisquitetroublesomeandrelativelyslow.Themagneticcorethatisnotselectedwhenreadingisthesameaswhenwriting,itwillnotchangethemagneticstateandgenerateinducedcurrent,soitwillnotbereadandwillnotinterferewiththeselectedmagneticcoretoreaddata.
Thereisadifferencebetweenmagneticcorememoryandourgeneralstorageconcept,thatis,undernormalcircumstances,thewritingofamemoryisalwaysslowerthanreading,butthemagneticcorememoryisonthecontrary,itisreadingItisslowerthanwritingbecauseitsreadingisdestructive,soreadingmustincludeawritingprocesstorecoverdata.
Description
Theterm"core"comesfromatraditionaltransformerwhosewindingsurroundsthecore.Incorememory,wirespassthroughanygivencore-theyaresingle-turndevices.Thepropertiesofthematerialusedforthememorycorearesignificantlydifferentfromthepropertiesofthematerialusedforthepowertransformer.Themagneticmaterialusedinthecorememoryrequiresahighdegreeofmagneticremanence,theabilitytomaintainahighdegreeofmagnetization,andalowcoercivity,therebyrequiringlessenergytochangethedirectionofmagnetization.Thecorecanadopttwostates,onebitiscoded,anditcanbereadwhenthe"sensingline"is"selected".Evenifthememorysystemispoweredoff(non-volatilememory),thecorememorycontentwillberetained.However,whenthekernelisread,itisresettoa"zero"value.Then,thecircuitryinthecomputermemorysystemrestorestheinformationintheimmediaterewritecycle.
Toiminta
Tietokoneen päämuistissa käytetyn ydinmuistin yleisin muoto,X/Ylinecoincidence-virta, koostuu suuresta määrästä pieniä renkaanmuotoisia ferromagneettisia keraamisia ferriittejä (magneettisydäminen)Muo verkkorakenne (järjestetty"sydämen"pinotuiksi kerroksilla, joita kutsutaan nimellä. varhaisessa järjestelmässä oli neljä riviä:X,Y,Sense ja Inhibit, mutta myöhemmissä ytimissä on myöhemmin kaksi riviä yhdistetään Sense/ Estolinja.Jokainen silmukkakela tallentaa yhden bitin(0 tai 1).Yksi bitti jokatasollavoidaan käyttää yhdessä syklissä, jotenjokainen konesanasanajoukko on jaettuAbunchof"tasoihin".Jokainen taso toimii yhdellä sanalla rinnakkain, sallienkokosanan lukeataikirjoitettuna.
ThecorereliesontheferriteusedtomaketheringThe"squarering"characteristicofthebulkmaterial.Thecurrentinthewirepassingthroughthecoregeneratesamagneticfield.Onlyamagneticfieldgreaterthanacertainstrength("selection")cancausethemagneticcoretochangeitsmagneticpolarity.Inordertoselectthememorylocation,XandYOneofthelinesisdrivenbyhalfofthecurrent("halfselection")tocausethischange.Onlythecombinedmagneticfield(logicalANDfunction)generatedattheintersectionoftheXandYlinesissufficienttochangethestate;theothercorescanonlyseetherequiredfieldsHalfofthevalue("halfselection"),ornoneatall.Bydrivingthecurrentthroughthewireinaspecificdirection,theinducedfieldgeneratedforcesthemagneticfluxoftheselectedcoretocirculateinonedirectionortheother(clockwiseorcounterclockwise)Onedirectionisstored1andtheotherisstored0.
Thetoroidalshapeofthemagneticcoreispreferablebecausethemagneticcircuitisclosedandtherearenomagneticpoles,sothereislittleexternalmagneticflux.ThisAllowsthecorestopackcloselytogetherwithoutallowingtheirmagneticfieldstointeract.Alternating45-degreepositioninginthecorearrayhelpsreduceanystraycoupling.
Readingandwriting
ForreadingTakesomecorememory,andthecircuittriestoflipthebittothepolarityspecifiedasthe0statebydrivingtheselectedXandYlinesthatintersectatthecore.
1,josbitti on jo0,ytimen fyysiseen tilaan ei vaikuta.
2.Jos bitti oli 1,ydin muuttaa magneettista napaisuutta. Viiveen jälkeen tämä muutos aiheuttaa jännitepulssin Senseline-linjaan.
2.p>
Detectingthiskindofpulsemeansthatthebitrecentlycontains1.Theabsenceofapulsemeansthatthebitcontains0.Thedelayofdetectingthevoltagepulseiscalledtheaccesstimeofthecorememory.
Aftersucharead,thebitcontains0.Thisexplainswhythecorememoryaccessiscalledadestructiveread:anyoperationtoreadthecorecontentserasesthesecontentsandmustberecreatedimmediately.
Inordertowritesomecorememories,thecircuitassumesthatthereisareadoperationandthebitisinthe0state.
Towrite1bit,drivetheselectedXandYlines,currentdirectionandreadoperationThedirectionisopposite.Likereading,themagneticcoreattheintersectionoftheXandYlinesischanged.Changemagneticpolarity.
Towrite0bit(inotherwords,write1bitisprohibited),thesameamountofcurrentwillbesentthroughtheInhibitline.Thisreducesthenetcurrentflowingthroughthecorrespondingmagneticcoretohalfoftheselectedcurrent,therebysuppressingthechangeinpolarity.
Theaccesstimeplustherewritetimeisthememorycycletime.
Otherformsofcorememory
Wordlinecorememoryisusuallyusedtoprovideregistermemory.Othernamesforthistypearelinearselectionand2-D.Thisformofcorememoryusuallywoventhreelinesthrougheachcoreontheplane,wordread,wordwrite,andbitsensing/writing.Toreadorclearaword,applyfullcurrenttooneormorewordreadlines;thiswillcleartheselectedcore,andanytriggerwillgenerateavoltagepulseinitsbitread/writeline.Forreading,usuallyonlyonewordreadlineisselected;butforclarity,multiplewordreadlinescanbeselectedwhileignoringthebitsense/writeline.Towriteaword,ahalfcurrentisappliedtooneormorewordwritelines,andahalfcurrentisappliedtoeachbitsense/writelineforthebittobeset.Insomedesigns,thereadwordandwordwriterowsarecombinedintoasinglewire,resultinginamemoryarraywithonlytwowiresperbit.Forwriting,multiplewordwritinglinescanbeselected.ThisprovidesaperformanceadvantageoverX/Ylinecoincidencecurrent,becausemultiplewordswiththesamevaluecanbeerasedorwritteninasinglecycle.Atypicalmachineregistersetusuallyusesonlyasmallplaneofthisformofcorememory.Usethistechnologytobuildsomeverylargememories,suchastheextendedcorestorage(ECS)auxiliarymemoryintheCDC6600,whichhasupto2million60-bitwords.
Anothertypeofcorememorycalledcoreropememoryprovidesread-onlystorage.Inthiscase,thecorewithmorelinearmagneticmaterialisonlyusedasatransformer;noinformationisactuallystoredintheindividualcores.Eachpartofthewordhasacore.Readingthecontentsofagivenmemoryaddressgeneratesacurrentpulseinthewirecorrespondingtothataddress.Eachaddresslinepassesthroughacoretorepresentbinary,oroutsidethecoretorepresentbinary.Asexpected,thekernelismuchlargerthantheread-writekernel.Thistypeofmemoryisveryreliable.AnexampleistheApolloguidancecomputerusedforlunarlandings.
Features
Theperformanceofearlycorememorycanbecharacterizedintoday’sterminologyasverysimilartoaclockrateof1MHz(equivalenttohomecomputersintheearly1980s,suchasAppleIIandCommodore64).Thecycletimeoftheearlycorememorysystemwasabout6μs,whichhaddroppedto1.2μsintheearly1970sand600ns(0.6μs)inthemid-1970s.Somedesignshavehigherperformance:ThememorycycletimeoftheCDC6600in1964was1.0μs,andthecoreusedrequiredahalf-selectcurrentof200mA.Doeverythingpossibletoreduceaccesstimeandincreasedatarate(bandwidth),includingusingmultiplecoregridsatthesametime,eachgridstoringonedataword.Forexample,amachinemayuse32corenetworks,eachcorehasonebitofa32-bitword,andthecontrollercanaccesstheentire32-bitwordinasingleread/writecycle.
Corememoryisnon-volatilememory-itcanretainitscontentsindefinitelywithoutpower.ItisalsorelativelyunaffectedbyEMPandradiation.Theseareimportantadvantagesforthefirst-generationindustrialprogrammablecontrollers,militarydevicesandaircraftsuchasfighterjets,andspacecraftapplications,andleadtothecoresbeingusedformanyyearsaftersemiconductorMOSmemoriesareavailable(seealsoMOSFET).Forexample,thespaceshuttleIBMAP-101Bflightcomputeroriginallyusedcorememory,andretainedthememorycontentevenwhentheChallengerdisintegratedin1986andsubsequentlyplungedintothesea.[16]Anotherfeatureoftheearlycoreisthatthecoercivityisverysensitivetotemperature;theappropriatehalf-selectioncurrentatonetemperatureisnottheappropriatehalf-selectioncurrentatanothertemperature.Therefore,thememorycontrollerwillincludeatemperaturesensor(usuallyathermistor)tocorrectlyadjustthecurrentlevelfortemperaturechanges.AnexampleofthisisthecorestorageusedbyDigitalEquipmentCorporationforitsPDP-1computer;thisstrategycontinuesthroughallsubsequentcorestoragesystemsbuiltbyDECforitsPDPair-cooledcomputerseries.Anotherwaytodealwithtemperaturesensitivityisto"stack"themagneticcoreinatemperature-controlledoven.ExamplesofthisaretheheatedaircorestorageoftheIBM1620(itmaytake30minutestoreachoperatingtemperature,about106°F(41°C))andtheheatedoilbathcorestorageoftheIBM7090,theearlyIBM7094sandIBM7030.
Thecoreisheatedratherthancooled,becausethemainrequirementisaconsistenttemperature,anditiseasier(andcheaper)tokeepthetemperaturemuchhigherthanroomtemperatureratherthanequaltoorlowerthanroomtemperature.
In1980,thepriceofa16kW(kilowatt,equivalentto32kB)corememoryboardinstalledinaDECQ-buscomputerwasaboutUS$3,000.Atthattime,thecorearrayandsupportingelectroniccomponentsweremountedonasingleprintedcircuitboardwithasizeofapproximately25×20cm,andthecorearraywasmountedafewmillimetersabovethePCBandprotectedwithametalorplasticboard.
Diagnosinghardwareproblemsincorememoryrequiresrunningtime-consumingdiagnosticprocedures.Althoughthequicktestcheckswhethereachbitcontains1and0,thesediagnosticprogramsusetheworst-casemodetotestthecorememoryandmustrunforseveralhours.Sincemostcomputershaveonlyonecorememoryboard,thesediagnosticprogramswillalsomoveinthememorysothateverybitcanbetested.Theadvancedtestiscalledthe"Schmootest",inwhichthesemi-selectedcurrentismodifiedwiththetesttime("strobe")ofthetestsenseline.Thedatagraphforthistestlookslikeacartooncharacternamed"Schmoo"withastuckname.Inmanycases,theerrorcanbesolvedbygentlytappingtheprintedcircuitboardwiththecorearrayonthedesktop.Thisslightlychangesthepositionofthecoresalongthewiresthatrunthroughthemandcansolvetheproblem.Thisprocessisrarelyneededbecausethecorememoryprovedtobeveryreliablecomparedtoothercomputercomponentsatthetime.