Multi-CPU Qbus VAXen

From: Antonio Carlini <>
Date: Fri Oct 10 13:03:40 2003

> I've been planning a monster like this, 4 small backplanes
> mounted in a
> hacked-around wide cabinet, 4 processors running as a VAXcluster over
> Ethernet...

If you mean 4-way multiprocessing, then 2-way was almost
certainly done at some time (probably in DECwest). I'm not
sure 4-way is practical, at least not with 4 backplanes. If
you want them all in one backplane you probably have to remove
(or otherwise inhibit) the bus terminating resistors on 3 of
the processors.

As others have pointed out, it doesn't really get you anywhere since
there is no real shared memory between the processors (they could
each have their own via PMI or they could all share some Qbus
memory - neither is an appealing option). You would also have the
minor problem that no OS would be able to do much with the
slave processors. (In fact, I think all the Oses I know of
probably wouldn't even notice them, so they would probably
boot as though they were on a MicroVAX II (or III if you used
KA65x processors).

If OTOH you meant 4 separate BA23 boxes each with its
own processor all in a VAXcluster, then that's just
independent MicroVAXes ... I had racks like that in
the lab at DEC. But that's less exciting than pushing
the boundaries I guess. You don't need a hacked cab,
just an ordinary 19" rack will do ... I kept back-to-back
VAX 4000s or MicroVAX IIIs in the bottom
to save space and make *absolutely* sure the rack
could not be tipped :-)

Antonio Carlini   
Received on Fri Oct 10 2003 - 13:03:40 BST

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