Source : Free On-Line Dictionary of Computing

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 different
        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}.
     
        (1999-08-01)