Understanding Computer Terms
CD-ROM drive
A drive that reads a CD-ROM (or music CD) by shining a laser into the clear plastic base and interpreting the way the laser light is reflected by the shiny aluminum layer. The CD-ROM drive is read-only; it cannot write to a disc. Most modern drives can also read a CD-R (unless written in multi-sessions by a CD-RW drive). Only the newest multi-session CD-ROM drives can read a CD-RW written in multi-sessions.
CD-ROM XA
“XA” stands for Extended Architecture. CD-ROM XA is an extension of the Yellow Book standard, generally consistent with the ISO 9660 logical format, but designed to add better audio and video capabilities taken from the CD-I standard so that a CD-ROM could more easily be used for multimedia applications. CD-ROM XA was abandoned as an independent multimedia format, but Photo CDs are written in the CD-ROM XA physical format.
CD-RW (CD-Rewritable)
Media used in a CD-RW drive to record data that can be overwritten thousands of times. The clear plastic base is molded with a spiral track to ensure that the CD-RW drive follows the same spiral path as the one stamped on a conventional CD. The middle (recording) layer is a phase-change crystalline mixture. Sandwiched between two layers that draw away excess heat during the writing process, the phase-change layer gives the disc a metallic grey color. The media can be used for single-session or multi-session writing (recording different tracks on different occasions). Advanced multi-session technology is not backward-compatible. Only multi-read capable CD-ROM and newer DVD-ROM drives can read CD-RWs written in multi-sessions. Because of the lower reflectivity of the phase-change recording layer, older CD players and CD-ROM drives cannot read CD-RWs, even when written in a single session. CD-RW technology is improving, but the quality of recordings is not yet comparable to CD-R recordings.
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