http://www.pctechguide.com/09cdr-rw.htm
The links off this page illustrate and explain the material science of
CD-R and CD-RW fairly accessibly (AFAIK; I have no background in
this). From this gloss, it appears as if one would need to work quite
hard to derive any information from an erased CD-RW or from a CD-R
burned to opacity. In the former case, it is conceivable to laymen
(such as myself) that certain areas may be more or less reflective
(since the melted recording layer might not be as reflective as a part
of the disk that had never been absorbant) in a way that could lay the
data within a tolerance of a more sensitive reader, but I'm confident
the reality is more complex than this overview. If, for example, one
could induce the parts of the disk that had once been absorbant to
become so again (with, say, less energy than would be required of
those parts that had always been reflective), then restoring it could
be possible.
Is there a materials scientist in the house? -C
On 7/15/05, Erik Fichtner <emf@obfuscation.org> wrote:
Frank Knobbe wrote:
I would assume that there are tiny
indentations that remain from a previous burn of a given dimple that
might be observable through electron microscopy. Is anyone aware of such
research?
CD-RW uses a temperature sensitive layer that either crystallizes or
does not crystallize depending on which temperature the "write beam"
was at for that bit. What I am unclear on is if the CD-RW media
is uniformly distributed in the "plastic sandwich" that makes the disc,
or not. I *assume* that it is, purely from a manufacturing
standpoint. If that is the case, then it might be possible that
two different CD-RW drives erase different portions of the bit on the
disc, resulting in a condition similar to what happens on magnetic
media. I would suspect that the same drive would write in the same
place, but I could be very wrong there.
--
Erik Fichtner; Unix Ronin
"Mathematics is something best shared between consenting adults
in the privacy of their own office" - Adam O'Donnell
