All,

Regarding heat and magnetic media.

CD-R's use a laser to spot heat a small portion of the spinning disc to help
coerce the magnetic domains.

Remember "bias" on your audio cassette deck?   The bias provided a strong
enough field to allow the signal to impress itself on the tape.   The bias
signal is strong enough to momentarily heat the media.

The critical temperature for a magnetic medium is called the Curie point.
As I recall the Curie point for audio magnetic tapes that point is less than
150 degrees F.
Try this recipe:
On a hot day leave a cassette tape in your car in the sun.   Let cook.
Pick up tape.    "Ouch that's #%! (past the Curie point!)"   Drop tape on a
hard surface.  Past the Curie point a sharp physical jar will partially
erased the tape.

Wirt Atmar wrote in message ...
>Magnetic domains (the 1's and 0's)
>are "reset" at sufficiently high temperatures. The reset temperature varies
>from material to material, but you can be sure that at sub-molten
>temperatures, some or all of the magnetic information will be lost

- Cortlandt