Multiprocessor Qbus PDP-11

Zane Healy healyzh at
Fri Aug 20 20:55:07 CDT 2021

On Aug 20, 2021, at 1:39 PM, Paul Koning via cctalk <cctalk at> wrote:
> Interestingly enough, I remember another machine that was also called 11/74; it existed in the RSTS/E lab in Merrimack (NH).  That one wasn't an MP machine; instead, it was an 11/70 with additional microcode to add the CIS (strings and decimal arithmetic) instruction set.  COBOL-11 could use this, and indeed CIS was a supported product in some later machines.  But the 11/74 CIS machine never saw the light of day.
> I don't know why not.  Perhaps it was not cost-effective given that it was a physically large machine, no longer a state of the art architecture for the time (around 1980).  One comment I heard is that it was forced to be canceled because it could run COBOL faster than a VAX-11/780. No idea if that was true (either the speed claim or the cancelation claim).  It has a faint ring of plausibility to it; when the 780 came out, DEC made some noises that PDP-11 would disappear within just a handful of years.  It didn't take them all that long to realize the absurdity of that notion.
> 	paul

Given what happened with the PDP-10, it seems very plausible that it was canceled due to the VAX-11/780.


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