RSTS / Simh disk drive confusion

From: Paul Koning <>
Date: Thu Sep 23 16:42:39 2004

>>>>> "Al" == Al Kossow <> writes:

 Al> Best rule for SIMH or E11 purposes is NOT to mix "RM" and "RP"
 Al> drives on a single RH11/RH70.

 Al> --

 Al> There was some discussion/questions from Bob Supnik about this on
 Al> the simh developers list this week if mixed drives were or were
 Al> not supported on the PDP11 operating systems. It sounded like
 Al> they were not, so I'm surprised that they may have been on V9 and
 Al> earlier.

 Al> The problem comes about because the RM and RP massbus controllers
 Al> have slightly different register sets.

No they don't.

The RH11/RH70 is the same either way. What changes is the registers
in the disks -- RP and RM disks are very similar but not identical.

Working from memory now -- I believe the correct statement is that
RSTS has always allowed mixing them on either of the two massbus
controllers, for access within the OS. The place you run into issues,
prior to RSTS 9.0, is when booting. Some vague memory says that your
boot device (unit 0) on the primary massbus should be an RP04/5/6 and
not an RM if you mix them.

If you run RSTS 9.0 or later, mix at will and boot at will, it all

Received on Thu Sep 23 2004 - 16:42:39 BST

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