UK PDP11 wanted

Johnny Billquist bqt at
Sat Apr 11 09:33:48 CDT 2015

On 2015-04-11 16:26, Noel Chiappa wrote:
>      > From: Pete Turnbull
>      > Are you confusing it with a KDJ11-A ... But this is a KDJ11-B
> Nope. Have several of both (IYWR, it was my looking at my various M8190's
> that led me to the conclusion that all M8190's, no matter the version, can
> do PMI).

As far as I know, that is correct.

>      > Basically what makes the difference is whether it's using PMI memory or
>      > QBus memory. ... If you change the config to not use PMI, an 11/83
>      > becomes an 11/73.
> After thinking about this for a while, the terminology does now make sense to
> me, if it's applied to _systems_, not _boards_.


> An 11/73 is a _system_ with no PMI memory usage (one can of course plug PMI
> memory into a system with an M8192, but that won't make it use it, i.e.
> become an 11/83). An 11/83 is a _system_ with PMI memory in use (an M8190,
> plus PMI memory).


> But I still think of the _cards_ as either an '11/73 CPU' (M8192) or
> '11/83-84 CPU' (M8190).

I understand that, but it don't really make sense, as the M8190 can 
exist both in an 11/73 and an 11/83 (and also the 11/84).

> The '11-83/84' part does lead to an interesting question: what do we call a
> _system_ with an M8190, a KTJ11 (M8191), and no PMI memory, only regular QBUS
> memory? (Not sure if this will work... but it should, I'll try it soon and
> see. Also, this part is for fun, not serious!)

Should not work, as far as I know.
The CPU bus on an 11/84 is always PMI. It is not a Qbus.

> Analogizing to the 73/83 distinction, one might say that it's not an 84, but
> a '74'... but that number is already taken! :-)

Right. Apart from the fact that you cannot put Qbus memory in an 11/84. 
However, you could put Unibus memory on the system, I think. But it will 
not be that usable, as it will only exist in the 18-bit address space.


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

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