22 Nov
2019
22 Nov
'19
11:09 a.m.
On 11/22/19 1:01 PM, Paul Koning via cctalk wrote:
But being a fixed head drive, the RS04 has no seek
latency, so probably faster overall than a moving
head drive.
We had an RS04 swap device on our 11/70 at Purdue Electrical Engineering Network running
BSD Unix.
It had been running for so long that the disk/head lubricant had worn away. If it was ever
spun
down, it would have to be hand spun to overcome the initial friction, but then it was
fine.
--tom
On Nov 21, 2019, at 10:13 PM, Chris Zach via
cctalk <cctalk at classiccmp.org> wrote:
I *think* (and this is putting the wayback hat on) that the RH11 originally was the
controller for the RS03 and RS04 fixed head disk drives. The dual Unibus was so you could
put them on Unibus A for talking to the 11/45's main bus with data transfers ripping
across Unibus B directly to the dual-ported memory on the 45.
Thus one of the Unibus ports didn't need to worry about arbitration (it was the only
thing on the bus) and could stream data from the (very quick) RS03/04's right into
memory for the ultimate swap device.
Nice swap device, certainly. But the RS04
isn't actually all that fast. The book says 4 microseconds per word, compare that
with the RP04 at 2.5 microseconds per word. I remember we got an RP04 on our college
11/45 in 1974 or early 1975, but that one still had an RF11 swapping disk. So it's
not clear to me which came first. The 2020 takes
advanatge of this with the dual unibus adapter, one talks to the chatty stuff like the
DZ11's, the other has no arbitration issues as it sucks data down from the faster
spinning RM03s without timeouts.
RH11 machines could use the RM02 but not RM03;
that one was supported only on the 11/70 because of its speed. But it's way faster
than these other disks we mentioned. And then there was the RP07, which was never
officially supported on any PDP11 even though it did work fine on an 11/70; it was the
"super large" disk on the main RSTS/E development system.
One of my long term questions has been to see if
a 2020 could talk to a RM80. It should be possible as the Massbus personality module talks
to the bus at 3600 RPM just like the RM03, and they did manage to get the R80 to talk to
the 11/730 with a dedicated memory channel connection (though maybe the R80 was heavily
interleaved)
If it can handle an RM03, then I'd expect an RM80 should work also
since it transfers at the same speed.
paul