PDP-11/74 MP

John Forecast john at forecast.name
Mon May 18 10:46:39 CDT 2015

CASTOR:: was the M+ group’s 11/74 housed in it’s own machine room in ZK. Since the machine hardware could be relatively easily reconfigured, POLLUX:: was reserved for when the system was running as 2 independent nodes (3+1 or 2+2 CPUs). The DECnet group had a dual processor system with node name ELROND::.

I used CASTOR:: standalone a couple of times while debugging the MP changes to the DECnet kernel code until ELROND:: became stable. Eventually, ELROND:: became the timesharing system for the DECnet-RSX group.

The lack of cache-coherency and the limited work-arounds (cache-bypass or cache flushing) meant that all the DECnet kernel code, both drivers and protocol stack, ran with cache-bypass enabled on its data PDRs. So the networking code on an MP system had lower peak performance than on a normal 11/70 although you would never notice the difference in regular operation.


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