19 Apr
2009
19 Apr
'09
11:55 a.m.
On 19 Apr 2009 at 18:57, Tony Duell wrote:
Random though (I've not tried anything like
this..) Most of those
speed control circuits used an AC tachogenerator built into the drive
motor. Provided the beld doesn't slip, or you have a direct-drive
motor (common in half-height drives) you should get a constant number
of cycles from that generator per revolution. Could you divide that
down to produce hard sector pulses?
It's a possiblility, although it would be drive-specific. As I've
mentioned, I don't have any systems that require HS drives; I just
did this as an exercise.
Another random thought.... Most of these hard-sector
drives were
single-sided. Most modern drives are double-sideed. How about
recording timing pulses on the normally unused side of the disk and
adding extra electronics to the drive (basiclaly just a second read
amplifier chain) to pick them up and produce sector pulses? Some hard
drives used divided-down signals from the sevo surface for this sort
of thing.
Certainly, but again, drive-specific rather than a general solution.
I suspect that there's also considerably more "drag" caused by a
5.25" drive jacket and that it's less constant than what one would
find in a 3.5" rigid-jacketed drive. All in all, a 3.5" is probably
a better choice, but doesn't address the issue of using either HS or
SS media in the same drive.
I also considered an "embedded sector" solution wherein a disk would
be pre-formatted with a unique pattern) that could be easily detected
by external circuitry, conditioned by a timing window. (Isn't that
called an "Address Mark? :) )
Whether or not the system using it would over-write the pattern is
another issue.
But there's more than one way to skin a cat, eh?
--Chuck