Re: CD Technology

[shack@southwind.net (Randy Shackelford)]

In article <389F751E.B258B20B@ripco.com>,
Jonathan Schattke  <wizwom@ripco.com> wrote:

>>      CD's do not depend upon magnetic storage; so, there does not seem to any
>> need for them to contain magnetic materials. CD's are read by laser beams.
>> The aluminum or whatever inside the plastic probably has little tiny blips
>> created by a laser during recording which are detected during playback.
>
>CD's bear a lot of resemblance to a phonograph record.  There are divots in the
>surface which are read by the laser.  The originals (and current music and
>CD-ROMS) are made by a one-time mastering process which blasts the aluminum with
>a laser, abating material; then a micro-accurate cast is made of the original,
>and it is cast in aluminum as many times as the producer wishes.
>
>Writeable CDs use a magneto-optic or dual-level process to heat a special
>material disk.  They are much more expensive to manufacture, thus the higher
>price.  If they must be writable multiple times, then the process must also be
>reversible, adding further expense.

Actually recordable CDs use a dye layer which is melted during writing to make
pits which are read the same way as those on manufactured CDs. RW discs have
material which allows data to be written, then can be erased via an annealing
process, which restores the surface to a state where it can be writtten on
again.

BTW both Rs and RWs are seriously cheap these days, with Rs under $1 each
and RWs approaching the dollar mark. Gotta leave this newsgroup from time
to time and see what's happening in the current state of the industry.
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