Re: the net is falling and I want my mommy again

In message <slrngkv5dv.drb.pm@xxxxxxxxxxxxxxxxxxxxxxx>, Paul Martin
<pm@xxxxxxxxxx> writes
In article <MyLk+PCkdnTJFwUJ@xxxxxxxxxxxxxxxxxx>,
Robert Sneddon wrote:
Any form of writeable or rewriteable disc works only by changing the
reflective index of the track under the reading optics

Rewritable discs have an approximately similar reflection
characteristic as the front layer in a double layer DVD.

A pressed DVD/CD/Blu-ray disc has pits which are best when it comes to
reading data off the disc as the read head can use optical interference
to get a nice clear on-off signal. Any rewritable disc format doesn't
have pits (although they do have a wobbly groove for the R/W head to
follow, known as the "pre-groove"). Double-layer pressed discs are read
by refocussing the read laser onto the second pitted surface. Getting
rewritable dual-layer discs to work (read or write) involves arcane
practices which may be familiar to an old SCSI-II haruspexer.

Back in the good old days during the runup to DVD being released VOZ
demoed a ten-layer optical disc prototype which they claimed they could
read perfectly. Their marketing geniuses asserted that the then-current
requirement for a six-foot long solid granite optical bench to do the
deed could be easily consumerised to three pieces of transparent plastic
costing 37 cents quantity 10,000 as it was a SMOOE. Yeah, right.
--
To reply, my gmail address is nojay1 Robert Sneddon
.