25 Nov
2005
25 Nov
'05
8:58 p.m.
On 11/25/2005 at 2:29 PM Allison wrote:
Yes, 1meg was way above the usual 190k-380k common for
for DDDS drives.
The highest I got to with MFM was 800k (80tr 2sided).
The FDC board itself has 56 ICs, counting the 1781, and a fair number of
discretes. The next edition of the machine simply used a 179x and 96 tpi
drive for 720K, but it wasn't nearly as real-estate hungry. IIRC, the 1781
was a marginal design; it had a nasty tendency to hang unexpectedly, so a
latch was added for the software to toggle the reset pin. I can't even
find a datasheet for it anymore.
The disk that Shugart used while innovative was really
bad for
repeatability of position and slooowwww.
I wondered how well that disc would wear, but then Shugart had lousy drive
electronics too, so it didn't matter in the long run.
We used a Micropolis leadscrew drive as our calibration diskette writer.
We disconnected the stepper on the positioner and hooked a 100:1 reduction
drive onto it and drove it with a separate stepper. Took forever to get
from cylinder 76 to 0, but it worked just fine.
Cheers,
Chuck