Compact disc,or as it is better known,CD,was the most widely used optical format.CD drives were standard on many microcomputer systems.Typically,CD drives can store from 650 MB to 1 GB of data on one side of a CD.

There are three basic types of CDs:read only ,write once,and rewritable.

Read only——CD-ROM,which stands for compact disc-read-only memory,is similar to a commercial music CD.Read only means it cannot be written on or erased by the user.Thus,you as a user have access only to the data imprinted by the publisher.CD-ROMs are used to distribute large databases and references.They also are used to distribute large software application packages.

Write once——CD-R,which stands for CD-recordable,can be written to once.After that they can be read many times without frterioration but cannot be written on or erased.CD-R drives poften are used to archive data and to record music downloaded from the Internet.

Rewritable——CD-RW stands for compact disc rewritable.Also known as erasable optical discs,these discs are vert similar to CD-Rs except that the disc surface is not permanently altered when data is recorded.Because they can be changed,CD-RWs are often used to create and edit multimedia presentations.