Prime 2550 in the UK

Robert Ollerton rollerton at
Mon Apr 24 23:41:44 CDT 2006

If I recall DOS was the single user OS they picked up from the
government (MIT & NASA?).  The multi-user version of it was Primos III
for the Prime 300, and then Primos IV was the breakthru with big
virtual memory space and a lot of other advanced (for then) and
Multics derived features.

On 4/24/06, Dennis Boone <drb at> wrote:
>  > Also, I wouldn't think the OS tapes for the 2550 would work on the
>  > 750 which is a much older system. But, I really don't know!
> There were not, during the period I worked on Primes, variants for
> different hardware.  Once Primos started supporting a new type of
> hardware, it rarely stopped -- backwards compatibility was one of
> the albatrossen which sank the company, IMHO.  Even the hardware had
> the disease.  How many architectures do you know of which had working
> support for 7 or 8 completely different addressing models, complete
> with the predictable effects on the assembler language?  The machines
> I worked on in the mid-late 80s still had 16S mode support, which if I
> understand correctly, was essentially the architecture Prime inherited
> from the old H316/516 machines used in the early Internet IMPs.
> There are older machines which were NOT 50-series hardware, which ran
> some older ancestral version than the Primos IV which ran on the -50s.
> But Primos IV for 50 series should run on virtually anything from a
> 250 on up.
> Those tapes should work just fine on a 750, if they're readable at all.
> De

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