Alan Dowds wrote:
>
> Just a thought.
>
> Why didn't Sony make MD double sided? Could have followed the analogue
> cassette analogy (!) and given twice the recording time for almost the same
> cost?
MD is like CD. The active layer is on the top of the disc, and the disc
itself is optically clear. The laser shines through the disc and hits
the top layer from below. MD is also MO technology and during
recording, the laser heats the active layer to its Curie point while a
magnetic head sits directly above the laser and polarizes the active
layer appropriately. I believe for MO to work, a magnetic head has to
be directly above the laser. At any rate, this would prevent the
ability of MD to be a dual-sided media.
Now perhaps using CD-RW technology (phase change?), it could be
double-sided. However, this would require the active layer to be
sandwiched in the middle. Not to mention this adds complexity in that
there would need to be dual optical pickups on both sides of the disc to
read each side. This is far simpler in magnetic media (like 3.5"
floppies and hard drives) where the heads are tiny, but in an optical
media, the optical blocks are very large. I think a dual-sided portable
player would be extremely large.
Now if MD were double-sided and required flipping the disc (like
non-autoreverse cassette players)... I think that would just suck!
Flipping discs would be very annoying!
Shawn
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