Multiprocessor Qbus PDP-11

Guy Sotomayor ggs at
Fri Aug 20 15:07:41 CDT 2021

There were a couple of other PDP-11 multiprocessors that I know of (and 

  * C.MMP (eventually 16 PDP-11/40e's in an SMP configuration with a
    crosspoint switch accessing a large memory).  It ran a capability
    based OS called Hydra.
  * CM*  this was a cluster of LSI-11s (as I recall) that were
    hierachially interconnected to allow for distributed operation (I
    think it was potentially capable of running with 255 nodes). I don't
    recall what OS CM* used.

Of course both of the above did not use off the shelf OS's or software.

TTFN - Guy

On 8/20/21 12:41 PM, Alan Frisbie via cctalk wrote:
> Charles Dickman <chd at> wrote:
> > There are indications in the KDJ11-B processor spec on bitsavers that
> > the M8190 could be used in a multiprocessor configuration. For
> > example, bit 10 of the Maintenance Register (17 777 750) is labeled
> > "Multiprocessor Slave" and indicates that the bus arbitrator is
> > disabled. There is also section 6.6, "Cache Multi-Processor Hooks",
> > that describes cache features that allow multiprocessor operation.
> >
> >Would it be as simple as connecting to 11/83 qbus together? And adding
> > the proper software.
> >
> > Anybody ever heard of such a thing?
> Such a system was put together and tested at DEC with the RSX group
> (who did the PDP-11/74 multiprocessor work).  I'm told that while it
> worked, it wasn't terrible successful, and the project was abandoned.
> I was given a gift of one of the CPU modules that was used in the test
> and I might still have it around here.  I can't recall for certain,
> but I think the module required some ECOs to make it work in a
> multi-processor configuration.
> The person to ask about this, Brian McCarthy, is unfortunately no
> longer with us.  :-(
> Alan Frisbie

TTFN - Guy

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