🚀 go-pugleaf

In article <watnot.12152> ccplumb@watnot.UUCP (Colin Plumb) writes:

>They didn't carry it as far as possible, but Commodore varied the clock rates
>on their 5-1/4" drives for the PETs and C-64s.  The difference was, I believe,
>between 17 sectors on the inner tracks and 21 on the outer ones (don't quote me
>on those figures).
>
>You could do the same thing on an optical disk, since data-storage applications
>don't require constant bit-rates, the way real-time audio output does.

Real-time audio output probably doesn't require constant bit-rates either.
I believe that CD players read bits into a buffer asynchronously, and then
put the bits out to the D-to-A at a precisely clocked rate.  At least that's
how I would do it.  That would avoid the need for an extremely accurate drive
motor.  Variable bit density on the disk would only affect the rate at which 
program material enters the buffer.   As other contributors to this discussion
have noted, variable bit rates would involve some computational overhead, and
it's not clear how much this would slow things down.  In addition, it may be
that for audio CD's the nominal bit-rate on the rotating medium is closely
tuned to the bandwidth of the channel to the buffer, so that doubling the
bit-rate might require some redesign.  For audio applications there's no
incentive for anyone to do this.  (If you could double the amount of program
material on a CD, do you think people would be willing to pay $30 each instead
of $15?  Most people think CD's are overpriced anyway.)  For information
storage there probably would be;  if for a relatively small additional cost an
optical drive could store 2Gbyte instead of 1Gbyte per platter, I'd buy that
machine..  For audio applications the bucks are in selling disks;  for data 
processing, the bucks are in selling machines.

Peter S. Shenkin	 Columbia Univ. Biology Dept., NY, NY  10027
{philabs,rna}!cubsvax!peters		cubsvax!peters@columbia.ARPA