RSTS / Simh disk drive confusion

From: Paul Koning <>
Date: Fri Sep 24 11:57:35 2004

>>>>> "John" == John A Dundas, <John> writes:

 John> Paul, At 11:47 AM -0400 9/24/04, Paul Koning wrote:
>> BTW, you're correct to say that four massbus controllers can exist
>> in an 11/70. At least for RSTS, the rule is that one is for
>> tapes, one for RS03/04, and two for the RP/RM massbus disks. The
>> tapes massbus could have on it any mix of massbus tapes, and the
>> RS03/04 massbus would accept any mix of those two drives, but
>> mixing more than that wasn't allowed.

 John> Didn't remember those details. Thanks.

>> Clearly it would have been possible to make the device drivers
>> more general, so (for example) TU16 and RP04 could live on the
>> same massbus, or 32 RP/RM disks could be supported, 8 on each --
>> but there never was any push for that and the code doesn't work
>> that way. (Some vague memory says that VMS did have more
>> flexibility in this area -- or was it TOPS-10?)

 John> Do the restrictions specify _which_ RH is for tape, RS, disk?
 John> Or just that only two for RP/RM, 1 for tape, 1 for RS and it
 John> can be any of the four?

The former. The tape RH is at 772440, the RS RH is at 772040, and
the other two (776700 and 776300) are RP/RM. That roughly matches
what the PDP11 architecture handbook shows for assignment. However,
it says that the 776300 address is "alternate RS/RP/RM/TJ when for
RSTS it's only RP/RM. It also says that there's a fifth RH11/RH70
address, 775400 for the TU78. RSTS doesn't support that address and
doesn't seem to support the TU78 (too fast for a PDP11, I think).
Instead it knows that address as a "KXJ11-CR" whatever that may be.

Received on Fri Sep 24 2004 - 11:57:35 BST

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