The SIMH PDP-10 simulator from Richard Cornwell was updated to his Version 3 recently.  See his posting to the SIMH message board on

Having learned that it was supporting the DBD9 disk images for RP07, I decided to set up his version to boot my KLH10 images of TOPS-20 7.1 (my PANDA and SRI hybrid).

Things did not go particularly well, however.

I copied my system disk images (A dual-RP07 pair), and booted to standalone.  I disabled most all services (networking, etc) in TOPS-20 and then shut down.  I then disabled networking (the NI20 device) in SIMH, and then booted again.

Once booted, I ran a Dhrystone test on the Cornwell's SIMH PDP-10 (KL10B) and under KLH10.

SIMH reported 12936 dhrystones/second.

KLH10 reported 28355 dhrystones/second.

This was all fine and well, as I didn't expect SIMH to perform as fast as KLH10.

The problems encountered were due to the crashes that occur when booted under SIMH when any code compiled with the KCC C compiler is run.  Many programs seem to just hang, but can be stopped with ^C.   Some sort-of work, but TTY output is problematic.  A simplified UNIX cat(1) program doesn't output to the TTY correctly.  And many programs will crash TOPS-20.  While I'm aware that there is code in KLH10 to accommodate the "Panda Lights" console-light hardware, I do not know of any changes to the underlying machine simulation particular to the Panda or SRI TOPS-20 kernel changes, nor any changes made to accommodate KCC C-generated machine code.

There is also something amiss with the SIMH PDP-10 timer support.  Calls to the DISMS monitor JSYS result in waits (dismissals) that are 4 to 5 times longer than the milliseconds requested.   That is, a one-second wait/dismissal request doesn't return for 4-5 seconds.  Timer-based macro programming through DISMS is failing under SIMH.

I may investigate the SIMH  PDP-10 issues/limitations at a later date.  For now, I have satisfied my curiosity about the SIMH-based PDP-10 simulation functionality.