GLOSSARY
CYLINDER
Onseveraldisksurfacessharingacommonrotationalaxis,theaggregateoftracksata givenradialposition.Asetofdisktracksthataresimultaneouslyunderthesetofread/
CYLINDER ZERO
Theoutermostcylinderinadrivethatcanbeusedfordatastorage.
D
DATA
Anorderedcollectionofinformation.Inaspecificcase,itistheinformationprocessed byacomputer.
DATA SEPARATOR
Anelectroniccircuitwhichdecodesplaybackdataandproducesseparateclockanddata bits.Sometimesincorrectlyusedtodenotedatasynchronizer.
DATA SYNCHRONIZER
Anelectroniccircuitproducingaclocksignalthatissynchronouswiththeincoming datastream.Thisclocksignalisthenusedtodecodetherecordingcodebeingusedinto userdata.
DATA TRANSFER RATE
Inadiskortapedrive,therateatwhichdataistransferredtoorfromthestorage media.Itisusuallygiveninthousandsofbitspersecond(Kbit/second)ormillionsof bitspersecond(Mbit/second).
DEDICATED LANDING ZONE
Adesignatedradialzoneonthediskwherecontactstartingandstoppingoccurby design.
DEDICATED SERVO
Aservoschemeinwhichaprerecordedpatternonanotherwiseunuseddisksurface providespositioninformationtotheservocircuitrybymeansofaheadreadingthat surface.
DEFECT
Amagneticimperfectioninarecordingsurface.
DEFECT MANAGEMENT
Ageneralmethodologyofavoidingdataerrorsonarecordingsurfacebyavoidingthe useofknownbadareasofmedia.Usuallydefectivesectorsortracksareretiredanddata arewritteninalternatelocations.Severalalgorithmsarepossiblesuchas“sector slipping,”or“sparesectorpertrack.”
DEFECT MAP
Alistofdefectsthatfallwithinapass/failcriteriaofauser.Thislistisusuallyusedbyan operatingsystemoradiskdrivecontrollerfordefectmanagement.
DEFECT SKIPPING
Adefectmanagementschemeforavoidingsurfacedefects.Ithasdatawrittenbeforeand afterthedefect,insteadofusingalternatetracksorsectorstoavoiduseofthedefective area.
DENSITY
Generally,recordingdensity.Seeareal,bit,andstoragedensity.
DC ERASE
ThemethodoferasingatrackusingaDCwrite/erasecurrentthrougheitheraRead/ WriteorErasehead.
DIGITAL
Anysystemthatprocessesdigitalbinarysignals(havingonlyvaluesofa1or0;usually inbitsandbytes)ratherthananalogsignals(signalsthatcanhavemanyvalues)
DIGITAL MAGNETIC RECORDING
Seemagneticrecording.
DIRECT ACCESS
Accessdirectlytomemorylocation.(Seerandomaccess).
DIRECT MEMORY ACCESS
Ameanofdatatransferbetweenthedeviceandhostmemorywithoutprocessor intervention.
DIRECTORY
Alistingoffilesmaintainedbythediskoperationsystem(DOS)oradatabase managementsystemtoenableausertoquicklyaccessdatafiles.
DISK
Aflat,circularpieceofmetal(usuallyaluminum)orplastic(usuallymylar)witha magneticcoatinguponwhichinformationcanberecorded.(See,forexample,floppy diskorWinchesterdisk)
DISK DRIVE OR DISK MEMORY DEVICE
Thetotalelectromechanicalstoragedevicecontainingdisksandread/writeheads,head positioningmechanism,drivemotor,andelectronics.
DISK PACK
Anumberofmetaldiskspackagedinacanisterforremovalfromthediskdrive (predecessorofWinchestertechnology).
DISK OPERATING SYSTEM (DOS) Themastercomputersystemprogramthatschedulestasks,allocatesthecomputersystem resources,controlsaccessestomassstoragedevices,managesfiles,andsoforth.Typical
DISK STORAGE
Auxiliarymemorysystemcontainingdiskdrives.
DISK TRANSFER RATE
Theratethatdigitaldataistransferredfromonepointtoanother.Expressedineither bits/secondorbytes/second.
DOUBLE FREQUENCY ENCODING
AnothernameforFMencoding.Thisisbecauseallpossibledatacombinationswill resultinonlytwopossibletemporaldisplacementsofadjacentdatabits,specifically “1F”and2F.”
E
EARLY WINDOW
Adatawindowthathasbeenintentionallyshiftedintimeinanearlydirection.
EMBEDDED SERVO
Aservotechniqueusedfortrackfollowing.Positioninformationisprerecorded betweendataareasinatracksothatadatahead,andproperadditionalcircuitry,can determinethedataheadlocationwithrespecttothecenterpositionofthetrack(or cylinder)inquestion.
ERASE
Aprocessbywhichasignalrecordedonamediumisremovedandthemediummade readyforrerecording.
ERROR CORRECTION CODE (ECC)
Amathematicalalgorithmthatcandetectandcorrecterrorsinadatafield.Thisis accomplishedwiththeaidofCheckBitsaddedtotherawdata.
ERROR FREE
Arecordingsurfacethathasnodefects.
ERROR RATE
Thenumberoferrors(typemustbespecified)thatoccurinaspecifiednumberofbits read.
ERROR RECOVERY PROCEDURE
Theprocessthatoccursinresponsetoadataerror.InadrivewithoutECC,this
EXTRA PULSE
Termusedinsurfacecertification.Itiswhenafluxfielddiscontinuityremainsafterthe recordingsurfaceiserased,therebyproducinganelectricaloutputofareadhead passingovertheareawiththediscontinuity.Anextrapulseoccurswhentheelectrical outputislargerthanaspecifiedthreshold.
F
FEEDBACK
FETCH
Areadoperationanditsrelateddatatransferoperations.
GL – 2
