do you know variety of optical discs???

actually now a days.these a lot of optical disc in use for secondary storage.It can save the data up to 50 gigabytes.by using laser beam to the surface of disc the data will be transmit,it difference from hard disk that use magnetic to transmit the data.
let take a look to the variation of optical disc..
~compact disc known as CD-
it was widely use and standard on many microcomputer.               
there 3 basic type of CD.
$.read only:mean the data cannot be written or erased by user.CD-Because of this feature and their large capacity,ROMs are a great media format for retail software.The first CD-ROMs could hold about 600 MB of data, but now they can hold up to 700 MB.Its similar commercial music CD.get it from: http://www.techterms.com/definition/cdrom
$.write once:A compact disc on which you can write only once and thereafter is read-only memory
$.Reriteable:CD format that allow erasing of previous recorded information and writing of new information on the same physical location.
~now we go next type of optical disc.It was Digital Versatile Disc(DVD)
A compact disk designed to store large amounts of data, especially high-resolution audio-visual material.these has 3 type of DVD
$.read only:also known as DVD Player.using for distributing music.
$.write once:these drive as usually use to create permanent data for large amount of data.
$.Rewriteable:DVD+RW,DVD-RW, DVD-RAM
lastly is High Definition :Disc optical disc that has a capacity of 25 to 50 gigabytes