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(CD-RW) A rewritable version of CD-ROM. A CD-RWdrive can write about 650 megabytes of data to CD-RW mediaan unlimited number of times. Most CD-RW drives can alsowrite once to CD-R media.CD-RW media cannot be read by CD-ROM drives built prior to1997 due to the reduced reflectivity (15% compared to 70%) ofCD-RW media.CD-RW drives and media are currently (1999) more expensivethan CD-R drives and media. CD-R is sometimes considered abetter technology for archival purposes as the data cannot beaccidentally modified or tampered with, and encourages betterarchival practices.Standard prerecorded CDs have their information permanentlystamped into an aluminium reflecting layer. CD-WR discs havea phase-change recording layer and an additional silver(aluminium) reflecting layer.A laser beam can melt crystals in the recording layer into anon-crystalline amorphous phase or anneal them slowly at alower temperature back to the crystalline state. The differentreflectance of the areas make them appear as the 'pits' and'lands' of a standard CD.Phillips: New Technologies(http://www-us.sv.philips.com/newtech/cdrewritable.html).See also CD-R and DVD-RAM.