> On Jan 16, 2023, at 11:47 AM, Chuck Guzis via cctalk <cctalk@classiccmp.org>
> wrote:
>
> The 844 drives date from the early 70s. ...
>
> Can't tell you more about the mechanics of the things--I haven't seen
> one of these in many many years. They were the workhorse drive for CDC
> large systems for quite some time. We used them on the STAR-100, for
> example.
On the CERL PLATO system at U of Illinois, around 1977, we had 20-ish 844-21
drives, and maybe a few 844-41 as well. Those were roughly the same as the DEC
RP04 and RP05 drives, same pack and track count. Different sectors, though;
322 12-bit words per sector.
Those are 3600 rpm drives, linear voice coil head actuator, dedicated servo
surface. The details of the format was handled in a sort of microcoded bit
handling engine, one of two engines in the programmable controller (7054). I
actually have the source code still around, and the manual for that beast also
still exists.
My favorite for wild mechanics is the IBM 1311 we had on an IBM 1629 Mod II.
Those have hydraulic actuators, 100 cylinders. In the controller, the
subtractor that would tell the machinery how many cylinders there are between
the current one and the requested one was an optional feature ("direct seek
option") which we didn't have. Without the option, all seeks would be done by
retracting all the way to cylinder zero, then back out again the number of
cylinders corresponding to what the program asked for. You could really make
the drive shake by feeding it a simple program that stepped through the
cylinders; near the end of the loop it would spend a significant fraction of a
second getting from, say, track 98 to 99.
paul
