CHAPTER 13

754 Chapter 13 Optical Storage
Because of the differences required in the High-Speed media (discs), they can be used only in High-
Speed CD-RW drives. If you try to write on the High-Speed media in a 2x or 4x CD-RW drive, the
recording will fail and you will possibly see several error messages. Note that you can use the slower
4x or less rated media in the High-Speed drives, providing you write at only the 4x or lower speed for
which the media is rated.
Mount Rainier
Mountainier is a new standard being promoted by Philips, Sony, Microsoft, and Compaq; it enables
native operating system support for data storage on CD-RW. This makes the technology much easier
to use (no special drivers or packet-writing software is necessary) and enables CD-RW drives to
become a fully integrated storage solution. The main features of Mount Rainier are
■ Integral defect management
■ Direct addressing at the 2KB sector level
■ Background formatting
■ Standardized command set
■ Standardized physical layout
This standard requires support directly in the operating system, BIOS, and requires drives with modified
firmware and design. If it catches on, it might change the way CD-RW drives are used in 2002
and later.
MultiRead Specifications
The original red and yellow bookThe original Red and Yellow Book CD standards specified that on a
CD the landsshould have a minimum reflectance value of about 70%, and the pits should have a
maximum reflectance of about 28%. This means that the area of a disc that represents a land should
reflect back no less than 70% of the laser light directed at it, whereas the pits should reflect no more
than 28%. In the early 1980s when these standards were developed, the photodetector diodes used in
the drives were relatively insensitive, and these minimim and maximum reflectance requirements
were deliberately designed to create enough brightness and contrast between pits and lands to accommodate
them.
On a CD-RW disc, the reflectance of a land is approximately 20% (plus or minus 5%), and the reflectivity
of a pit is only 5%, obviously well below the original requirements. Fortunately, it was found
that by the addition of a relatively simple AGC circuit, the ratio of amplification in the detector circuitry
can be changed dynamically to allow for reading the lower-reflective CD-RW discs. Thus,
although CD-ROM drives were not initially capable of reading CD-RW discs, modifying the existing
designs to enable them to do so wasn’t difficult. Where you might encounter problems reading CD-
RW discs is with CD audio drives, especially older ones. Because CD-RW first came out in 1996 (and
took a year or more to become popular), most CD-ROM drives manufactured in 1997 or earlier have
problems reading CD-RW discs. Reflectivity is also a problem on DVD-Video and DVD-ROM drives—
because they use a different frequency laser, they actually have more trouble reading CD-R discs than
CD-RWs.
DVDs also have some compatibility problems. With DVD, the problem isn’t just simple reflectivity as
it is an inherent incompatibility with the laser wavelength used for DVD versus CD-R and RW. The
problem in this case stems from the dyes used in the recording layer of CD-R and RW discs, which are
very sensitive to the wavelength of light used to read them. At the proper CD laser wavelength of
780nm, they are very reflective, but at other wavelengths, the reflectivity falls off markedly. Normally,
CD-ROM drives use a 780nm (infrared) laser to read the data, whereas DVD drives use a shorter