A CD-R works by generating a high-powered laser beam that physically melts
a pit, or darkens the reflective properties of special CD blanks. A CD-R,by
definition, makes a permanent record; once a pit is burned or darkened, it
cannot be undone. Once recorded, it cannot be changed.
CD-Rs use a higher-powered focused laser beam that goes through the top
layer to reach a temperature-sensitive recording layer. When writing informa-
tion to the disc, the CD-R beam creates a pinpoint of heat of about 200° Celsius
(about 400° Fahrenheit), which melts a tiny hole in the recording layer. An
organic dye on the disc melts into the hole to create a reflective spot. When the
CD-R is reading back the information on the disc, it uses the same laser beam,
at a much lower intensity, to scan the disc. The pits or holes reflect light back
to a sensor at different brightnesses, and these pulses are converted to 0s and
1s of data.
Over the years, engineers have come up with a number of dyes and other
compounds for use with CD-Rs; the goal has been to improve the capacity,
life, and speed of the discs (and to reduce prices). The most common early
organic dyes included compounds of green cyanine, gold phthalocyanine,
and silver-blue azo.
The difference between the various formulas may or may not make a differ-
ence on your CD-R. I have found that the discs from some manufacturers
work better in one computer than another, and it has not always been a
matter of price: Sometimes the less-expensive, non-name brand CD-Rs work
best because they are not expected to push the boundaries of speed or
capacity nor do they tout themselves as “Ultra Quality” or “Music Quality”
or “Our Discs Are Better Than Anyone Else’s.”
A somewhat common problem is that a disc recorded on your laptop may
work perfectly well when played back on that same machine but will not be
readable in a desktop machine, or the other way around. Or you may find
that a music CD you create on your laptop may not play on the CD in your
car. My recommendation: If you experience any problems making or playing
CD-Rs, buy a few samples of CD-Rs from various manufacturers and of differ-
ing colors and rated speeds and capacities and test them out to find the best
match for your setup.
How a CD-RW works...........................................................................
A later technology is the CD-RW,which is capable of reading, writing, and
rewriting CDs. They can record files to a disc, erase them, and rerecord them
much like a hard drive can be used over and over again.
Chapter 9: Going Round and Around: CD and DVD Drives 149