RSTS / Simh disk drive confusion

From: John A. Dundas III <>
Date: Fri Sep 24 11:06:07 2004


At 11:47 AM -0400 9/24/04, Paul Koning wrote:
> >>>>> "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.

Thanks for the explanation. I think the code fragment and
explanation you posted to SIMH explains this best.

>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.

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?)

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

>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.

I don't remember a DEC controller that did both MSCP and TMSCP
(though I'm certain someone will correct me if I'm wrong), so this
may be the motivation there. (Though almost certainly Emulex or
someone made a controller that would do both.)


Received on Fri Sep 24 2004 - 11:06:07 BST

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