RSTS / Simh disk drive confusion

From: Paul Koning <pkoning_at_equallogic.com>
Date: Fri Sep 24 10:47:08 2004

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

 John> Paul, While I'm willing to accept that mixed drive type strings
 John> are possible and supported, I don't see how the quote below
 John> supports that.

 John> At 8:04 PM -0400 9/23/04, Paul Koning wrote:
>> >> Best rule for SIMH or E11 purposes is NOT to mix "RM" and "RP"
>> >> drives on a single RH11/RH70.
>>
>> The thing I was trying to remember about mixed drives and booting
>> is described by this paragraph in the RSTS V9.0 Update Seminar
>> document (page 2-7): Multiple RH controllers for disks (DB and DR)
>> have always been supported by RSTS. The support for this has been
>> improved in V9 by allowing the booting of disks on either
>> controller regardless of drive type. Previously, there was a
>> restriction if the same drives were on different controllers, you
>> could only boot the one on the primary controller.
>>
>> So the answer for RSTS is (a) mixed drives are supported,

 John> That's not what I read in the statement above. IIRC, my /70
 John> supports up to 4 RH70s. The statement above seems to indicate
 John> that they removed a restriction where one must boot from drive
 John> 0 of a particular RH70. The statement itself doesn't indicate
 John> that I can have multiple drive types on the same RH70.

Actually, the old restriction wasn't quite as severe as you state it,
but yes, it doesn't directly address my claim. That's why I said "the
thing I was trying to remember..." because I knew there was SOME
restriction relating to drive mixing and the two moving head disk RH
controllers. The text I quoted states that restriction and the fact
it was removed.

>> (b) if you mix on both RP/RM massbus controllers, boot the primary
>> unless you're running V9.0 or later.

 John> Yes, I agree, this seems to be the case.

 John> Do you have something that explicitly states multiple drive
 John> types are supported on a single RH70?

Two things: my own memory from working in RSTS development, and
reading the code. I expect it's documented in user manuals, the
sysgen manual for example, but I don't have any of those.

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.

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?)

Similarly, I don't think that RSTS allowed mixing MSCP disks and TMSCP
tapes on the same controller. I don't really know that stuff -- it
may be that no PDP-11 MSCP controller existed that would do disk and
tape on the same controller anyway.

   paul
Received on Fri Sep 24 2004 - 10:47:08 BST