Hardware Reference
In-Depth Information
simply drag and drop or copy and delete files at will. Although CD-RW discs are about 1.5-2 times
more expensive than CD-R media, CD-RWs are still far cheaper than optical cartridges and other
removable formats. This makes CD-RW a viable technology for small-scale system backups, file
archiving, and virtually any other data storage task where rewritable DVD is not suitable.
Note
The CD-RW format originally was referred to as CD-Erasable, or CD-E.
Four main differences exist between CD-RW and CD-R media. In a nutshell, CD-RW discs are
• Rewritable
• More expensive
• Slower when writing
• Less reflective
Besides the CD-RW media being rewritable and costing a bit more, it is writable at speeds of no
more than 24x (about half the speed of the fastest CD-R discs). The actual top speed for a particular
drive and media combination is the slower of the drive or media speeds supported. This is because
the laser needs more time to operate on a particular spot on the disk when writing. This media also
has a lower reflectivity, which limits readability in older drives. Many older standard CD-ROM and
CD-R drives can't read CD-RWs. However, MultiRead capability is now found in virtually all CD
drives, enabling them to read CD-RWs without problems. In general, CD-DA drives—especially the
car audio players—seem to have the most difficulty reading CD-RWs. So, for music recording or
compatibility with older drives, you should probably stick to CD-R media. Check the drive or device
specifications to determine compatibility with CD-RW media.
CD-RW drives and media use a phase-change process to create the illusion of pits on the disc. As
with CD-R media, the disc starts out with the same polycarbonate base with a wobbled pre-groove
molded in, which contains ATIP information. Then, on top of the base a special dielectric (insulating)
layer is spin-coated, followed by the phase-change recording layer, another dielectric layer, an
aluminum reflective layer, and finally a UV-cured lacquer protective layer (and optional screen
printing). The dielectric layers above and below the recording layer are designed to insulate the
polycarbonate and reflective layers from the intense heat used during the phase-change process.
Figure 11.7
shows the CD-RW media layers, along with the pre-groove (raised ridge from the laser
perspective) with burned pits in the phase change layer.
