UK PDP11 wanted

Pete Turnbull pete at
Thu Apr 9 08:48:33 CDT 2015

On 09/04/2015 13:07, Noel Chiappa wrote:
>      > From: Pete Turnbull
>      >> Technically, that's an 11/83 CPU...
>      > Nope, it's only 15MHz ... and the MSV11-Q memory isn't PMI, so it's an
>      > 11/73.

> A discussion as to whether the addition of second board can change a first
> board from an A to a B would I suspect be non-productive, so I will pass over
> that point. :-)

Are you confusing it with a KDJ11-A - a dual-height board which is 
always an 11/73?  But this is a KDJ11-B, quad-height, which can be 
either 11/73 or 11/83.  This has been discussed a few times here on 
ClassicCmp, and elsewhere on DEC boards.  Basically what makes the 
difference is whether it's using PMI memory or QBus memory.  Originally 
11/73s were sold as 15MHz units in a non-PMI config.  Originally 11/83s 
were the same card[1] but running at 18MHz units in a PMI config.  If 
you change the config to not use PMI, an 11/83 becomes an 11/73.

[1] there are some early revisions that wouldn't work properly in all 
systems and where the DCJ11 wouldn't run at 18MHz or support a FPU

> One thing that I am curious about is the 15MHz aspect: what did DEC (if you
> recall) call a 15MHz M8190 paired with PMI memory?

An 11/83, because that's what all diagnostics, bootROMs, XXDP, RT-11 
RESORC, etc would report - assuming the PMI memory is ABOVE the CPU. 
But as far as I know DEC never sold them as such.  All the ones sold 
with 15MHz clocks were AFAIK sold with non-PMI memory.  And all the ones 
sold with an 18MHz crystal were sold with PMI memory as 11/83.


Pete Turnbull

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