On 26 Feb 2012 at 12:59, Fred Cisin wrote:
On Sun, 26 Feb 2012, Chuck Guzis wrote:
I don't know if it was the absolute slowest,
but the early single-
sided Micropolis drives (1015/16) were pretty darned slow--about 30
msec. track to track, if my memory is correct.
Certainly quite slow, but not as slow as 40ms Shugart SA400
I'd forgotten about the stupid 35-cylinder SA400 and the cam-follower
scheme. I hated it. It seems odd that anything could be slower than
a 4-step per cylinder positioner, but there you go.
What's strange is that at the time, most, if anot all 8" drives
positioned faster, and some even used a voice-coil setup.
And you're right--after things had worn in a little bit, the
positioner was a little less than accurate. The usual procedure in
case of error was to recalibrate (return to track 0), seek to
cylinder, retry 3 times; recalibrate and then to seek one cylinder
past the target and then step one back, then repeat 3 times; finally,
recalibrate then seek to one cylinder just before the targe cylinder,
then pause for a rev., then step one cylinder in and retry.
All of this to battle the backlash in the positioner mechanism.
--Chuck