24 Sep
2004
24 Sep
'04
11:57 a.m.
>>>> "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.
paul