Any own an 11/725...? arcarlini at
Mon Oct 24 14:51:57 CDT 2005

Tony Duell wrote:
>>> The 11/730, of course, is mostly PALs (as I said) with some RAM as a
>>> control store, 8 off 2901s as the ALU, and an 8085 (I think) to
>>> load the control store, etc. One day I am going to look into
>>> modifying the microcode of that machine...
>> To what end?  Increased performance?
> NO, just for fun... I doubt very much I could improve on the
> performance for running the VAX instruction set. I have not looked at
> the prints carefully enough to determine how much of the instruction
> set is hard-wired (if any), I wonder if it would be possible to run a
> different instruction set entirely.

I don't have an exact reference to hand, but one of the 
"how we built VMS for the uVAX-II" articles in one of the
DEC Technical Journals describes how they made a VAX-11/730
behave as a (then only proposed) MicroVAX-II. They did this 
to check the performance (and correctness) of the subsetting.
The 730 was chosen because it was entirely soft.

SO I guess you could make it do almost anything within
reason. Perhaps it could have been a faster PDP-8 than
the PDP-11/60 ... or given the 730's reputation, perhaps not :-)



Antonio carlini
arcarlini at

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