Drive Types There are two basic forms of optical storage used in computers today: compact disc (CD) and digital versatile disc (DVD). Compact disc storage was derived from the same media that we use from audio compact discs. There storage space averages around 650 to 700 MB of data per disc. They can contain audio, data or both on the same disc. Most software for computers is distributed on CD formats, though more and more these days software is coming out on DVD format as a DVD holds about 6 times the amount a CD holds. Optical drives can come as read only (ROM) or as writers (designated with either an R, RW). Read-only drives will allow you to only read or play data from discs that have data already on, they can not be used for removable storage. Writers or burners can be used to save data, create music CDs or video discs.     read CD write CD read DVD write DVD CD-ROM √ − − − DVD-ROM √ − √ − CD-RW √ √ − − DVD-ROM/CD-RW Combo √ √ √ − DVD-RW √ √ √ √