PDP-11/74 MP

Johnny Billquist bqt at update.uu.se
Tue May 19 20:38:01 CDT 2015

On 2015-05-18 17:46, John Forecast wrote:
> 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.

Thanks for the corrections and clarifications, John. I think I've heard 
this before, but my memory is constantly failing me.

Also, nice work! The DECnet code works just fine in MP.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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