Literally，multimediameanstwoormoremedia。Ifthepublisherofthisbookwantedtojointhecurrenthypeaboutmultimedia，hecouldadvertisethebookasusingmultimediatechnology。Afterall，itcontainstwomedia：textandgraphics。Nevertheless，whenmostpeoplerefertomultimedia，theygenerallymeanthecombinationoftwoormorecontinuousmedia，thatis，mediahavetobeplayedduringsomewell－definedtimedtimesinterval，usuallywiththeusersinteraction。Inpractice，thetwomediaarenormallyaudioandvideo，thatis，soundplusmovingpictures。

Inthemultimediaenvironment，wehavegraphicsandtextatthesametime，wecanalsoaddthephotograph，animation，good－qualitysound，andfullmotionvideo。Allofthetechnologiesmakecomputersmoreinterestingandmucheasiertouse。Forexample，amultimediaprogramcanplayasegmentofmovie：acatwasplayingareelofthread，withmewing…Thetableaucanabeimmediatelycapturedandpastedtoatextatthesideofaparagraphofwords。

CD－ROM

CD－ROMisanopticaltechnologythatisusedtomakecompactdisksforCDstereosystems;ithasnowbeenadaptedtostoredataforcomputers。CDdiskisanopticaldisc，onwhichdataisrecordedasasetofdipsinthesurface。Whenalaserbeamshinesacrossthedips，thereflecteddistortionrepresentsthedata。Opticaldischasa600megabytecapacityandarewellsuitedforthecomputerapplicationsneedingthevaststorage。Theplaybackeffectofopticaldiscsformusicisveryperfect，nohissandcrackleaswithotherphoto－records。AcomputersystemmusthaveaCDdriverthatisdesignedtoreadthedisksandtranslatethedataintoaformitcanprocess。CDdiskscanstorehugevolumesofdataandareveryusefulforreferencematerialanencyclopedia，forexample。However，asthenameimplies，CDdiskscannotbewrittenonorchangedinanyway。