Hardware Reference
In-Depth Information
levels to create amorphous and polycrystalline areas of low and high reflectivity, regard-
less of which state the areas were in prior. It is similar in many ways to writing data on
a magnetic disk that also uses direct overwrite. Every sector already has data patterns, so
when you write data, all you are really doing is writing new patterns. Sectors are never
really erased; they are merely overwritten. The media in CD-RW discs is designed to be
written and rewritten up to 1,000 times.
The original Orange Book Part III Volume 1 (CD-RW specification) allowed for CD-RW
writing at up to 4x speeds. New developments in the media and drives were required to
support speeds higher than that. So in May 2000, Part III Volume 2 was published, defin-
ing CD-RW recording at speeds from 4x to 10x. This revision of the CD-RW standard is
called
High-Speed Rewritable
, and both the discs and drives capable of CD-RW speeds
higher than 4x will indicate this via the logos printed on them. Part III Volume 3 was pub-
lished in September 2002 and defines Ultra-Speed drives, which are CD-RW drives cap-
able of recording speeds 8x-24x.
Because of the differences in High-Speed and Ultra-Speed media, High-Speed media can
be used only in High-Speed and Ultra-Speed drives; Ultra-Speed Media can be used only
in Ultra-Speed drives. Both High-Speed and Ultra-Speed drives can use standard 2x-4x
media, enabling them to interchange data with computers that have standard-speed CD-
RW drives. Thus, choosing the wrong media to interchange with another system can pre-
vent the other system from reading the media. If you don't know which speed of CD-RW
media the target computer supports, I recommend you either use standard 2x-4x media or
create a CD-R.
Because of differences in the UDF standards used by the packet-writing software that
drags and drops files to CD-RW drives, the need to install a UDF reader on systems with
CD-ROM drives, and the incapability of older CD-ROM and first-generation DVD-ROM
drives to read CD-RW media, I recommend using CD-RW media for personal backups
and data transfer between your own computers. However, when you send CD data to an-
other user, CD-R is universally readable, making it a better choice.
MultiRead Specifications
TheoriginalRedandYellowBookCDstandardsspecifiedthat,onaCD,thelandsshould
have a minimum reflectance value of about 70%, and the pits should have a maximum re-
flectance of about 28%. Therefore, 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
morethan28%.Intheearly1980swhenthesestandardsweredeveloped,thephotodetect-
ordiodesusedinthedriveswererelativelyinsensitive,andtheseminimumandmaximum
