Differences between PDP-11/83-84 M8190-AB/AC and AD/AE CPU cards

Henk Gooijen henk.gooijen at hotmail.com
Wed Feb 4 13:22:09 CST 2015

Without any checking, just digging in my "grey cells", so I could be wrong 
The 11/84 has all of its memory "elsewhere", that is *not* on the CPU 
The 11/94 has *all* memory that can be addressed *on* the CPU module.
So, the 11/94 has either 2MB or 4MB, what's installed on the module.
The performance gain of the 11/94 over the 11/84 is in fact the local 
If the 11/84 has 100% cache hits, it comes close to the 11/94. You could see
the 11/94 as an 11/84 with all memory as cache memory.
AFAIK, you cannot add memory to the 11/94 by adding a memory module
on the bus. The memory must be on the CPU module.

- Henk, PA8PDP

-----Oorspronkelijk bericht----- 
From: Noel Chiappa
Sent: Wednesday, February 04, 2015 6:40 PM
To: cctalk at classiccmp.org
Cc: jnc at mercury.lcs.mit.edu
Subject: Differences between PDP-11/83-84 M8190-AB/AC and AD/AE CPU cards

So I've seen some references which say that the M8190-AB and -AC (w-o/w 
FPP chip) are 15 MHz "11/73" CPUs for QBUS use, and the M8190-AD and -AE
(w-o/w FPJ11) are 18 MHz "11/83-84" CPUs for UNIBUS use (via the KTJ11-B
convertor, of course). (Of course, the /83 is nominally QBUS, but let's 
that for the moment... :-)

(And I'm not even going to try to give the KDJ11- suffixes that go with
these... :-)

However, I'm wondering if this is correct... I have a CPU board out of a 
(one owned by DEC, no less!) which says M8190-AB on the handles, but the 
crystal says "18.432", and it has a 57-19400-09 J11 chip, which seems to be
the 18MHz version (the 15Mhz seems to be -04).

Comparing it to a 'stock' -AB, this one seems to have the same 74S472 PROMs
(6 along the lower left-hand edge), PALs (top center and lower left), etc.
But they also match the ones on a 'stock' -AE, too!

So clearly an -AB/AC _can_ be _upgraded_ to an -AD/-AE... but are there
actually any differences between an -AB/AC and an -AD/-AE, other than the

I don't have my /84 up yet, so I can't plug a stock -AB in and see if it
works, but I'm starting to get the impression that except for the speed of 
J11 (and the crystal), and whether or not it came with the FPJ11, all four 
these boards are otherwise identical. Whether it's a 73, 83 or 84 depends
entirely on whether it has PMI memory and the KTJ11-B UNIBUS converter (and
the correct backplane, for the latter, of course).

Anyone have an confirmation one way or the other? Thanks!


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