17 Jan
2023
17 Jan
'23
9:58 p.m.
On Jan 17, 2023, at 3:45 PM, P Gebhardt via cctalk
<cctalk(a)classiccmp.org> wrote:
Am Montag, 16. Januar 2023 um 17:57:46 MEZ hat Chuck Guzis via cctalk
<cctalk(a)classiccmp.org> Folgendes geschrieben:
Hi Chuck,
No, 844 drives use linear voice coils (linear motors), which seems to have become the norm
in the early 1970s. RK05 is another example. The term "voice coil" is used
because they look like oversized versions of the coil that drives the speaker cone in
loudspeakers. These all are some sort of servo device; in many of them the servo signal
is on the media, but not always. For example, the RK05 uses a pattern of lines on a glass
substrate attached to the actuator; the "fault" light on the drive indicates a
failure of the light bulb that illuminates the servo pattern.
A common feature of linear motor actuators is an emergency retract circuit, powered by
rather large capacitors, to pull the heads off the disk if there is a power failure.
paul
The 844 drives date from the early 70s. I worked
for CDC on a military
project where these were brought in to replace the 821s that were bid
(yes, I know there's no information on those--they're essentially a
high-capacity unit build on an 808 chassis and unreliable as hell). A
typical installation might have used over 100 of the units on a 4-CPU
Cyber cluster. They worked well, unless one got a bad pack, which would
clobber the heads on a drive; using the drive on a new pack would result
in creating another head-clobbering pack. I recall an overnight report
issued by an operator where he succeeded in trashing several packs and
multiple drives in his attempt to get something to work. It was a
blow-by-blow report somewhat akin to the Gerard Hoffnung bricklayer story.
Wow, thanks for sharing this story!
Did the 844 drives have the same hydraulic-actuator approach like the MMD 841 drives?