1. Compact Disc Rewritable CD-RW A rewritable version of CD-ROM. A CD-RW drive can write about 650 megabytes of data to CD-RW media an unlimited number of times. Most CD-RW drives can also write once to CD-R media. CD-RW media cannot be read by CD-ROM drives built prior to 1997 due to the reduced reflectivity 15% compared to 70% of CD-RW media. CD-RW drives and media are currently 1999 more expensive than CD-R drives and media. CD-R is sometimes considered a better technology for archival purposes as the data cannot be accidentally modified or tampered with, and encourages better archival practices. Standard prerecorded CDs have their information permanently stamped into an aluminium reflecting layer. CD-WR discs have a phase-change recording layer and an additional silver aluminium reflecting layer. A laser beam can melt crystals in the recording layer into a non-crystalline amorphous phase or anneal them slowly at a lower temperature back to the crystalline state. The differen reflectance 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.
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