11/25/2014 Compact Disc Formats Explained

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PublishedinSOSJanuary1998:Closewindow

CompactDiscFormatsExplainedExplorationTechnique:Theory+Technical

ManyofuscannowaffordtheonceunthinkableluxuryofmakingourownCDs,foroneoffmusicdemos,massCDduplicationorgeneraldatastorage.Butfewofusknowthefullstorybehindthenumerous'Book'standardsgoverningthekindofdatathatcanbestoredonaCD.MIKECOLLINScoloursbynumbers...

NowthatyoucanbuyaCDrecorderforwellunder500,andnowthatsomecomputersarebeingsuppliedwitharecordableCDdrivebuiltin,ratherthanjustaCDROMplayer,morepeoplethaneverarestartingtomaketheirownCDs.ButCDscomeinlotsofdifferentflavoursthesedays:CDDA,CDROM,CDROM/XA,CDiandothertypes.TheirspecificationsarespeltoutinaseriesoftechnicaldocumentswhichareknownbythecoloursoftheircoversRedBook,YellowBook,GreenBook,OrangeBook,WhiteBookandBlueBookanditpaystoknowjustwhateachformatmeans.

HISTORY

TheCompactDiscwasoriginallydevelopedbyPhilipsandSonyasameansofdistributinghighqualityaudiotoconsumersareplacementforvinylrecords.TheCompactDiscDigitalAudioStandard,commonlyreferredtoastheRedBook,describesthephysicalandlogicalformatofthesediscs,whichstoredigitalaudiodatainaconvenientform.Butdigitaldataisdigitaldata,sowhynotuseCDsforotherformsofdigitaldata?Thesamethoughtthoughtoccurredtoothers,too,soextensionstotheRedBookstandardweredevelopedforstoringcomputerdata,compressedaudio,video,andgraphicalinformationonCD.Itisthesestandardswhicharenowtypicallyreferredtobythecolouroftheircovers.

TECHNICALLYSPEAKING

SoundOnSound:Est.1985

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DISCATONCEVSTRACKATONCE

Whenyou'rebuyingaCDrecorderitcanbeimportanttocheckwhetherit'scapableofrecordinginDiscAtOncemodeifyouwanttowritediscstomasterfrom,becausesomeCDrecorderscanonlywriteusingTrackAtOncemode.WithDiskAtOncerecording,thewholedisciswritteninonepasswithoutturningoffthelaser,whileTrackAtOncemodeonlyallowsyoutowriteonetrackatatime.WhenyouuseTrackAtOncemode,thelaserwillstopwritingbetweeneachtrack,butthelaserbeamdoesn'tturnoffimmediately,soacoupleofsectorsareallocatedattheendofeachtrackwhichwillbewastedasthelasershutsdown.Thesearecalledthe'runout'sectorsandaccountforthefactthatTrackAtOncerecordershaveafixedtrackspacingof2seconds.WithDiscAtOncemode,norunoutsectorsaregeneratedbetweentracks,sothepausebetweeneachtrackcanbeofanylength,andsongscanevenberuntogetherwithnogap.

Notethatifyou'remakingaudioCDstobecommerciallyproduced,therunoutsectorscreatedinTrackAtOncemodemaybeconsideredasunrecoverable'E32'errorswhenthediscischeckedatthepressingplant,andthediscmayberejectedasunsuitableforpressingfrom.Thissituationischanging,though.Reportedly,DougCarsonAssociates,whoprovideglassmasteringandformattransfersoftwaretopressingplants,havesolvedtheproblem.DCA'slatestsoftwareversionapparentlycheckstheTOContheCDRtofindoutwherethegapsare,andwheneveritfindsE32errorsthere(generatedbythelaserturningonandoffbetweentracks)itreplacesthemwithdigitalsilence.So,unlessyouhaveCDRswithE32errorsinplacesotherthanthegapsbetweentracks,pressing

Theinformationonallcompactdiscsisdividedintochunksofuniformsize,calledsectors,andadjoiningsectorsarethengroupedtoformtracks,whicharelistedinthedisc'sTableOfContents(TOC),aspecialunnumberedtrackthatplaysfirst.EverysectoroneverytypeofCDcontains3234bytesofdata,882bytesofwhicharereservedforerrordetectionandcorrectioncodeandcontrolbytes,leaving2352bytes(3234minus882)toholdaudiodatainaRedBookCDAudiodisc.Oneofthekeystounderstandingthedifferentformatsthoroughlyistolookathowtheotherformatsusethis2352bytesofspace.CDAudiodiscsusethespacefordigitallyrecordedsoundanderrorcorrectiondata,whileothertypesofCDsmaycontaincomputerdata,includingexecutableprograms,text,graphics,andcompressedaudioorvideo.

*REDBOOK

RedBookisthestandardforCompactDiscDigitalAudio(CDDA)andwasestablishedin1980asthefirstofthe'books'whichdefinedtheCDforaudiouseindomesticCDplayers.Toidentifythemselves,RedBookdiscsusuallyhavethefamiliar'CompactDiscDigitalAudio'logoprintedwithinthelabelarea.

TheRedBookstandardspecifiesthatacompactdisccanhaveupto99tracksofdata,witheachtrackcontainingasingleaudioselection.Thesetracksaredividedintoblocksofdatareferredtoassectors.Eachsectorholds3234bytesofdata,asmentionedearlier,arrangedas2352bytesofaudiodata,plustwo392bytelayersoferrordetectionanderrorcorrectioncodes(commonlyreferredtoasEDC/ECC),alongwith98controlbyteswhichareoftenreferredtoasthesubcodesorsubchannelsandaredesignatedbythelettersPthroughtoW.ThesecontrolbytescontainthetiminginformationwhichallowstheCDplayertocueinstantlytothebeginningofeachselection,displaytheselection'snumberandrunningtime,andprovideacontinuousdisplayofelapsedtime.

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plantsusingthelatestDCAsoftwarewillnotrejectCDRsmadeusingTrackAtOncemode.

*YELLOWBOOK

YellowBookisthestandardforCompactDiscReadOnlyMemory(CDROM),andthisextendstheRedBookspecificationbyaddingtwonewtracktypes:CDROMMode1andCDROMMode2.Mode1tracksaredesignedforstoringcomputerdata,whileMode2tracksstorecompressedaudio,videoandpicturedata.YellowBookdiscsusuallyhavethewords'DataStorage'insmalllettersbeneaththeCompactDisclogo.

Mode1sectorsincludeathirdlayerofEDC/ECCwhichimprovestheerrordetectionanderrorcorrectioncapabilitybyafactorof1000.Theextraerrorcorrectionisessentialbecausethismodeisdesignedforstoringcomputerdata,whereeventhelossofonebitofdatacouldbedisastrous.(Withaudio,theresultoflosingevenseveralbitsmaybeinaudible.)

CDROMtracksalsousepartofthespaceinthesectorsforsynchronisationdataandaheader.Letmeexplain:onanaudioCD,theinformationusedbythedrivetopositionthelaserpickupataspecificlocationiscontainedinthe'Q'subcode,andtheRedBookspecifiesthatthis'Q'channelinformationshouldpositionthepickuptoanaccuracyof+1second.Foraudioplaybackapplicationsthisdegreeofaccuracyisperfectlysufficient,butforcomputerapplicationsthedrivemustbeabletolocateandretrieveaspecificsectorwhichrequiresanaccuracyof1/75thofasecond.ItistoachievethisdegreeofpositioningaccuracythattheYellowBookspecifiestheinclusionofsynchronisationandheaderinformationineachsector.Thesyncbytesspecifiedoccurinaparticularpattern(0,followedby10bytesofFF,followedbyanother0)whichallowsthestartofeachnewsectortoberecognisedassuch.Theheadercontainstheabsoluteaddressofthesector,specifiedinminutes,secondsanddatablocks,andalsohasabytetoindicatewhetherthesectorisinaMode1orMode2track.

AswithRedBook,eachsectoronthedischolds3234bytesofdata,butMode1sectorsstartwiththe12bytesofsyncdata,followedby4bytesofheaderinformation.Thespaceforuserdatais2048bytesandthisisfollowedbytheextralayeroferrorcorrection,whichconsistsof4bytesofEDC,8bytesofblankspace,and276bytesofECC.Then,aswithallCDs,youhavethe882byteswhichcontainthefirstandsecondlayerRedBookstyleEDC/ECCandControlBytes.Mode2sectorsareprimarilyusedwheretheabsoluteintegrityofthedataisnotasimportantfor,say,audiooranimationsoMode2sectorsdonothavetheextralayeroferrorcorrection.Theydostillusethesyncandheaderinformation,though,sothereare2336bytesremainingfordata.

CDROM/XA(ExtendedArchitecture)discsweredevelopedtoallowaudioorvideotobeplayedbackatthesametimeascomputerdata.TheoriginalYellowBookCDROMsweredesignedforstoringandpublishingdatanotforplayingaudioorvideo.Theformatwasextendedin1988withtheadditionoftwo

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ABOUTTHEBOOKS

*SystemDescriptionCompactDiscDigitalAudio(RedBook),NVPhilipsandSonyCorporation.

*SystemDescriptionCompactDiscReadOnlyMemory(YellowBook),NVPhilipsandSonyCorporation.

*SystemDescriptionCompactDiscReadOnlyMemoryExtendedArchitecture(GreenBook),NVPhilipsandSonyCorporation.

*SystemDescriptionCompactDiscSystemsPartII:CDWO(OrangeBook),NVPhilipsandSonyCorporation.

newtracktypesMode2,Form1,andMode2,Form2whichhaveasubheaderfieldwithineachsectortodescribethesectorcontents.ThismakesitpossibletointerleaveForm1sectorscontainingcomputerdatawithForm2sectorscontainingaudio,videoorpicturedata,allwithinasingletrack.UsingspecialisedhardwareintheCDROMdrive,itisthenpossibletoseparatetheaudiodatasectorsfromthecomputerdatasectors,decompresstheaudiodataandplayitbackthroughtheCDROMdrive'saudiooutputs,whilesimultaneouslytransmittingthecomputerdatatoapersonalcomputerforprocessingordisplay.

ACDROMMode2,Form1sectorisidenticaltoaCDROMMode1sector,exceptthatthe8bytesofblanksinaMode1sectorhavebeenmovedtofollowtheheaderinformationwithinthesector,andareusedtoholdthesubheaderinformation.AswithMode1sectors,2048bytesareavailablefortheuserdata(normallycomputerdatawhichrequirestheextralayeroferrordetectionandcorrectionprovidedinMode1sectors).

AMode2,Form2sectoralsocontainsthesynchronisation,header,andsubheaderbytes,alongwiththe4additionalEDCbytesthatappearinMode1andMode2,Form1sectors.However,becausetheForm2sectorsareusedtoholdaudio,videoorpicturedatawhichdoesn'trequirethehighlevelofdataintegritynecessaryforcomputerdatathe276bytesoferrorcorrectiondatausedinForm1sectorsarenotincluded,leaving2324bytesavailableforuserdata.

CDROM/XAdiscscanbeplayedbackonpersonalcomputerswithsuitablehardwareandsoftware,andonspeciallyequippedCDROMdrivesorCDiplayers.CDROM/XAwasdevelopedasa'bridging'formatbetweenCDROMandCDi,andthismeansthatanapplicationdesignedforCDROM/XAcanbemadeplayableonaCDiplayersharingthesameaudioandgraphicsresources.AswithCDi,youcaninterleaveupto16hoursofADPCMcompressedaudiowithdata,toallowthedatatoberetrievedfromthediscwhiletheaudioplaysback.

*PHOTOCD

ThemostwellknownexampleofCDROM/XAdiscsarePhotoCDdiscs,EastmanKodak'sdigitalimagestorageanddistributionsystem.Youcannowgetyour35mmsnapshotssuppliedasdigitalfilesonaPhotoCDdiscfromBootsorotherplaceswhichprocessfilm.Discscanbewrittentousingmultisessionrecorders,sotheimagesdonothavetobeputontheCDdiscallatthesametime.Youcanfillpartofthedisc,takethishome,thentakethediscbacktoaddyournextandsubsequentrollsoffilm,until

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*UpdatetoSystemDescriptionCompactDiscSystemsPartII:CDWO(OrangeBook),NVPhilipsandSonyCorporation.

*SystemDescriptionCompactDiscBridge(WhiteBook),NVPhilipsandSonyCorporation.

*ISOStandard9660:InformationProcessingVolumeandfilestructureofCDROMforInformationInterchange.

FormoreinformationontheBookstandards,contactthefollowingaddress:

*AmericanNationalStandardsInstitute,1413Broadway,NewYork,NY10018.Tel:0012126424900.

thediscisfull.YoucanviewyourphotographsathomeonyourTVscreenusingaCDiplayeroradedicatedPhotoCDplayer,andyoucanalsoreadthefilesonaMacintoshcomputerusingsoftwaresuchasPhotoshop.

*KARAOKECD

KaraokeCDdiscsareanotherexampleofCDROM/XAdiscs,whichyoucanplayonadedicatedKaraokeCDplayeroronaCDiplayerequippedwithaDigitalVideocartridge(althoughCDidiscswillnotplayonaKaraokeCDplayer).KaraokeCDsusuallyhavetheword'Graphics'insmalllettersbeneaththeCompactDisclogo,andtheyfeaturefullscreen,fullmotionvideoandCDqualityaudiousingtheMPEG1compressionstandard.

*GREENBOOK

GreenBookisthestandardforCompactDiscInteractive(CDi)andisanextensionofYellowBooktoallowdiscstocontainamixofvideoandaudio,plusdatawhichtheusercancontrolinteractively,makingitidealforgames,encyclopaedias,educationalmaterialorbusinessapplications.CDidiscsuseMode2,Form1andMode2,Form2tracks,which,aswithCD

ROMXA,enablecomputerdataandcompressedaudio,videoorpicturestobeplayedbackatthesametime.

ACDiplayerlookssimilartoaCDAudioplayer,butyoucanhookituptoaTVoracolourmonitorandithasacomputerinsidewhichyoucancontrolusingahandheldremote.ThecomputerusesafairlyobscureoperatingsystemcalledOS/9,soCDitrackscannotbeplayedonnormalCDROMdrives.Ontheotherhand,CDiplayerscanplayaudioCDs,CD+Graphics(CD+G),PhotoCD,and,withaDigitalVideocartridge,KaraokeCDorVideoCDdiscsaprettyversatileplayer!

*ORANGEBOOK

OrangeBookisthestandardforwriteoncecompactdiscs.Thisspecificationcoversbothsingle(DiskAtOnce)andincrementalmultisession(TrackAtOnce)recording.Multisessionallowsyoutorecorda'session'topartofthediscandthenaddsubsequentsessionsatalaterdate,untilthediscisfull.Anewsessionwillcontainatableofcontentsfeaturingtheoldandthenewinformationonthedisc,soanyCDROMplayeryouwanttousetoreadamultisessiondiscneedstotakethisintoaccountbyreadingthelastwrittentableofcontentsordirectory.ManyolderCDROMdrivescannotreadmultisessiondiscs,so

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watchoutforthis.ThedisccansubsequentlybeconvertedtoaRed/Yellow/Greenbookdiscby'Finalising'thesession,toaddafinalTableOfContentswhichcanbereadbyanyCDROMplayer.

*WHITEBOOK

TheWhiteBookspecificationwasdevelopedtocovertheVideoCDformat,whichissupportedbyJVCandMatsushitaaswellasPhilipsandSony.TheseVideoCDdiscsareaspecialkindofCDROM/XAbridgediscthatallowyoutoplayfeaturefilmsandmusicvideosonadedicatedVideoCDplayer,oronaCDiplayerequippedwithaDigitalVideocartridge.AcomputerequippedwithaCDROM/XAdrive,anMPEG1decoderandahostplaybackapplicationcanalsobeusedtoplaythediscs,sotheycanalsobeusedforcomputerbasedtrainingapplications.BasedontheKaraokeCDstandard,VideoCDfeaturesfullscreen,fullmotionvideoalongwithwithCDqualityaudio,andisindependentofbroadcaststandardssuchasNTSCandPAL,so(unlikevideocassetteandlaserdiscformats)asinglediscplaysonanyVideoCDplatformworldwide.

*BLUEBOOK

BlueBookisthemostrecentofthe'colouringbooks'toappear,andthisspecifiestheCDExtrastandard,whichwasdevelopedasawaytoincludeCDROMdataonanaudiodisc.TheideahereisthatastandardaudioCDwillgiveupalittleofitsspacesothatyoucanincludeatrackofCDROMdatacontainingsomekindofinteractivedatarelatedtotheaudiowhichyoucanplayusingyourcomputer'sCDROMdriveandscreen.Thismightbeananimatedpresentationofsomeaspectoftheartist'swork,suchasexpandedsleevenotes,lyricsormusic,orjustsomewildlycreativeimagestoaccompanythemusic.Possiblyitcouldbea'taster'forafullblowninteractiveCDROMversionofthealbum.AlsoknownasEnhancedCD,aCDExtraisactuallyamultisessionCDwhichcontainsaudiotracksinitsfirstsession,followedbyadatatrackinthesecondsession.EarlyattemptstomakethiskindofCDsufferedfromtheproblemthatthefirsttrackwasthedatatrackandcouldproducealoudclickinginyourspeakersifyouinadvertentlytriedtoplayitdespitethelargewarningstickersonthepackagingtellingyounottodothis!ThiswasallsortedoutwiththeBlueBookstandard,sonowtheCDPlayerwillnotattempttoplaythedatatrack.

ALLABOUTFILEFORMATS

TheYellowBookstandarddidnotspecifyanyfileformats,soearlyCDROMdevelopershadto'rolltheirown'andthesewerenotcompatiblewitheachother.Fortunately,manufacturersquicklyrealizedthatstandardisationwasneeded,andtheInternationalStandardsOrganisationISO9660fileformatsubsequentlyemerged.YoucancreateapplicationsforMac,PCorUNIXsystemsusingthisfileformat,andyoucanevenhaveapplicationprogramsforallthreeplatformsononeCDROM,withallthreeabletoaccessthesamesetofdatafiles.TheproblemwithISO9660isthatitrestrictsdeveloperstoalowest

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commondenominatorintermsofhowmanycharacterscanbeusedforthefilenames,forinstance,sothisisnotsopopularanymore.

ItisperfectlypossibletodesignaCDROMforusewithoneparticularoperatingsystem,whichletsdevelopersusethefullrangeoffeaturesofthatoperatingsystem,suchaslongfilenames,desktopiconsandsoforth.So,forinstance,youcancreateCDROMdiscsinMacintoshHFSformatwhichwill'mount'onthedesktopofanyMacintoshcomputer,justasthoughtheyweredisksfromanyothertypeofdiskdrive.Thesecanholdupto650Mbofyourcomputerfilesinareadonlyformat.RewritableCDmachinesarebeginningtoappear,butthesearenotcommonlyinuseasyet,soyouwillmostlyencounterdiscswhichcanonlybewrittentoonce.

SUBCODES

EachsectoronanaudioCDcontainscontrolbytesidentifiedbythelettersPthroughtoW.Theseareoftenreferredtoassubchannelsorsubcodes,andthemostimportantarethefirsttwothePandQsubcodeswhichyoumayhaveseenreferredtointhismagazinebefore.

Forinstance,intheLeadInarea,theQsubcodecontainstheTableOfContents,whileintheProgramareaofthediscthePsubcodecontainsinformationaboutwherethemusicstartsandends,andtheQsubcodecontainsabsoluteandrelativetimeinformation.

Theothersubcodes,identifiedasRtoW,arenotalwaysused,butitisperfectlypossibletostoreadditionalinformationinthem.AnearlyextensionofthebasicCDformat,called'CD+g',usedthesebitstoaddgraphicsandMIDIdataforeachtrack,andsomespecialisedCD+gplayerswereproducedwhichhadvideoandMIDIoutputs.ThesewereneveravailableintheUK,asfarasIamaware.

TherearevariousothercodeswhichcanbesetforCDdiscsandwhichyouneedtobeawareof.Forexample,ifyouwanttomakesurethatalltherightsholdersgetpaidwhenyourdiscisbroadcast,youshouldbeincludinganISRCcode.ThisistheInternationalStandardRecordingCodewhichcanbeassignedtoeachandanyfinalmixtouniquelyidentifythismix.Thecodecanthenbeused,alongwithrecordskeptbytherecordcompanies,royaltycollectionorganisationsandrightsorganisations,totracktheownersandrightsholderswhoshouldbepaidwhentherecordingisbroadcastpubliclyorexploitedcommercially.

Ifthediscisreleasedcommercially,itwillalmostcertainlyincludeaMediaCatalogueNumber,whichisauniqueidentificationnumberfortheCDintheformofaUPCorEANbarcode.ThesecodenumbersareallocatedbytheEANorUPCauthoritiesandconsistof13consecutivedigitswhichareallocatedbyoneoftheseorganisations.

OlderDATandotherdigitalrecorderssometimesusedasystemof'preemphasis'onrecordedmaterial,withacorresponding'deemphasis'onplayback.PreemphasisbooststhehighfrequenciespriortoA/Dconversion,whiledeemphasisremovestheboostafterD/Aconversion.DeemphasiscircuitryisbuiltintoallCDplayerstoprovidecompatibilitywithanymaterialrecordedusingpreemphasis.However,theemphasisbitmustbesetto'on'inthetrack'sQcodesothattheCDplayerwillknowthatitshouldusethedeemphasiscircuitrywhilethistrackplaysback.

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EachtrackonaCDhasaCopyProhibit'flag'bitsettinginthetrack'sQsubcode,toindicatewhethercopyingthetrackisallowed.ThisCopyProhibitbitwasoriginallyintendedtopreventdirectdigitalcopyingusingDATrecorders,butvirtuallynorecordingequipmentusesthistoday,soithasnoeffectinpractice.Subsequently,theSerialCopyManagementSystem(SCMS)wasdevelopedtopreventusersfrommakingadigitalcopyofadigitalcopy.Inthissystem,theSCMS'flag'bitisincrementedwhenthesourcematerialisdigitallycopiedfromonedigitalrecordingdevicetoanother,soyou'reallowedtomakeonedigitalcopyofthesourcematerialusingSCMSequippedrecorders,butyouwon'tbeabletomakeanyfurtherdigitalcopiesofthatrecording.

Checkingthis'flag'onanyCDtracksbeforeyouwritetheCDidentifiesthesetracksasthefirstcopies,soyouwon'tbeabletorecordthemdigitallyfromtheCDontoanSCMSequippeddigitalrecorder.Ifyouwanttoallowdigitalcopiestobemade,don'tsettheSCMSflagsontheCD.Then,ifyouuseanSCMSequippedrecordertomakeacopyoftheCD,itwillbethefirstdigitalcopyandwillhavetheSCMSflagssetforeachtrackbythesystembuiltintotherecorder.Nowifyoutrytocopythatrecordingdigitally,SCMSwillpreventyou.

Bytheway,justincaseyouwerewondering,checkingSCMSwilloverridethesettingforCopyProhibit.

HybriddiscswhichwillworkwithMacandPCarealsoverypopular,asyoumightimagine.YoucancreateaCDROMwithbothMacHFSandISO9660filesystemswhichsharethesamedataandcanbereadonbothMacandPC.ThissolvestheproblemofhavingtoproduceaMacintoshspecificCDforMacintoshusersandanISO9660CDforPCandUNIXusers.

Youcanalsomixaudioandcomputerdataononediscinvariousways.Originally,amixedmodeCDwouldconsistofonedatatrackandseveralaudiotracks,withbothdataandaudiowritteninonesession.Thedatatrackwouldalwaysbeplacedintrack1justinfrontoftheaudiotracksonthediscwhichwasaproblem,asImentionedearlier,sincethedatatrackwouldproduceclicksinthespeakersifinadvertentlyplayedonanaudioCDplayer.Thismixedmodeformathaslargelybeensupersededbyanaudio/datamultisessionformatwherethefirstsessionconsistsofaudiotracksandthesecondsessionconsistsofdata.AnothertwistinthetaleisthatthissecondsessiondatacanbeinCDExtraformat,orinHFSorISO9660XAformats,orinMac/ISOHybridXAformatwhichmakestheformatevenmoreversatile!

Asyoumayalreadyhavegathered,amultisessiondiscissocalledbecauseyoucanwriteonesetofdatatofillpartofthedisc,andthenwriteone(ormore)additionalsetsofdatatofilltherestofthedisc.ThesesessionsarelinkedtogetherinsuchawaythatonlyonelogicaldeviceappearswhentheCDismounted.However,notallCDrecorderscanrecordthistypeofCDandnotallCDROMdrivescanreadthem.

A'multivolume'CDalsoconsistsofmultiplesessions,eachrecordedatadifferenttime,but,inthiscase,eachofthesessionsiscompletelyindependentoftheothers.WhenthistypeofCDROMismountedonyourcomputer'sdesktop,eachsessionwillappearasanindividuallogical'volume'.Inotherwords,ifyou

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AllcontentscopyrightSOSPublicationsGroupand/oritslicensors,19852014.Allrightsreserved.Thecontentsofthisarticlearesubjecttoworldwidecopyrightprotectionandreproductioninwholeorpart,whethermechanicalorelectronic,isexpresslyforbiddenwithoutthepriorwrittenconsentofthe

Publishers.GreatcarehasbeentakentoensureaccuracyinthepreparationofthisarticlebutneitherSoundOnSoundLimitednorthepublisherscanbeheldresponsibleforitscontents.Theviewsexpressedarethoseofthecontributorsandnotnecessarilythoseofthepublishers.

Websitedesigned&maintainedbyPBAssociates|SOS|RelativeMedia

PublishedinSOSJanuary1998

puttwosessionsonyourCDROMin,say,MacHFSformat,whenyouputthisintoyourMac'sCDROMdrive,twoiconswillappearonyourdesktop,eachrepresentingoneofthese'volumes'ofdata.Theselookandbehavejustlikeharddiskicons,exceptthatthereisasmalllockedpadlockinthetoplefthandcornerofthewindowwhichappearswhenyouopeneitherofthesevolumesontoyourdesktop.Thisindicatesthatthediscisreadonly.Again,notallCDrecorderscanrecordthistypeofCD,andnotallCDROMdrivescanreadthem.Finally,it'sworthnotingthatMacHFSCDROMscanonlybemultivolumeratherthanmultisession.