Optical Storage - Upgrading and Repairing PCs - page 674

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 about
half (or less) the speed of CD-R discs. 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 re-
flectivity, 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 vir-
tually 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,formusicrecordingorcompatibility witholderdrives,youshouldprobably
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.
Figure11.7 showstheCD-RWmedia layers, alongwiththepre-groove(raised ridgefrom
the laser perspective) with burned pits in the phase change layer.
Figure 11.7 CD-RW media layers.