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_at_world.std.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_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
>
Received on Fri Apr 16 1999 - 20:03:29 BST