On 8/2/2009 5:58 AM Robert Coe spake thus:

If you want to irretrievably destroy the data on a CD, scrape the
coating off of the "back" side; that's where the information is. The
reader looks through a layer of clear plastic, which effectively
protects the data from damage to the front side. That's why scratches
on the front side usually don't have much of an effect. And why users
should be more careful not to damage the back side than they usually
are.

Or so I've been told by those who know more about CDs than I do.

Take it from someone who used to work with CDs; you've got it pretty
much correct.

Actually, you don't even need to scratch off much of the coating to make
a CD unreadable and the data unrecoverable; a few well-placed scratches,
especially concentric with the disc, will do the job. That's because
you're destroying most of the data in each track. (This is why users are
advised to clean CDs only by wiping radially--from the center of the
disc towards the edge--rather than circularly; any damage done this way
will be distributed over different tracks, which reduces the risk of
unrecoverable read errors.)

BTW, I'm not sure that DVDs work entirely the same way.

Basically the same way, though as someone else pointed out, DVDs have
multiple layers. Still read from the "bottom" of the disc.


--
Found--the gene that causes belief in genetic determinism