16 Apr
1999
16 Apr
'99
8:03 p.m.
I had a number of double-headed drives, including Shugart 851's, Mitsubishi
whatevers, Qume DT-8's, and some NEC and Tandon half-height models, all of
which were operated at 3 ms. I've got the spec's for all of them so I can
verify whether they should indeed operate at that rate. Only the
single-headed drives were typically slower, IIRC.
The distinction, I believe, is that the "slow" drives use lead screws to
position the heads while the quicker ones use a band actuator. What I find
puzzling about this is that the 5.25" half-height drives, virtually all of
which were capable of the higher speed, were not set up for the higher speed
in the default on PC's.
I wasn't aware that the NEC controller chip had a problem with the step
rate. I stuck with WDC FDC chips in my own applications.
Dick
-----Original Message-----
From: Allison J Parent <allisonp(a)world.std.com>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Friday, April 16, 1999 6:35 PM
Subject: Re: 8" drive on a pc controller
<Please forgive my interloping, here, but my SHUGART
and Siemens SD 8"
drive
<are spec'd for 6 ms step rate, and the
double-headed types for 3 ms. It's
<really best (mechanically) to step these babies as fast as they will go,
an
<it's quieter too.
Be specific on the model as the sa800s and 850s would never do 3ms! Though
the later ones did step faster. The problem with 8" drives are that there
were some that were doing their best at 10-12mS and a few like CDCs 3ms
was the norm. Most fell in around 6mS.
ALSO, the PC controller uses the 765 chip (or it's core) generally and
that chip can truncate the first step pulse by 1/2mS (8/5"). So the
fastest recommended step rate programming (srthut in SPECIFY command)
is 4mS. I believe it was never fixed.
Allison