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.
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.
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)
C
On 11/21/2019 9:14 PM, Noel Chiappa via cctalk wrote:
> maybe the two can be jumpered together (the way the two UNIBI in the
> KD11-A/D can).
Actually, now that I think about it, that might be the reason for the order
of the UNIBUS A out B in/out slots in the backplane:
https://gunkies.org/wiki/RH11_MASSBUS_controller#Backplane_layout
One of those thin M9200 UNIBUS jumpers could be used to connect the A out to
the B in.
> Depends what you mean by "full-length"; no MUD (hex) slots, but yes to
> SPC slots (SPC)
Oooh, typo: 'SPC slots (quad)'
Noel
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