qbus module ID

From: Pete Turnbull <pete_at_dunnington.u-net.com>
Date: Sun Feb 6 06:32:04 2005

Executive summary at the end for those who don't want to wade through

On Feb 5 2005, 19:45, Jerome H. Fine wrote:
> >Pete Turnbull wrote:
> >>On Feb 5 2005, 21:17, Pete Edwards wrote:
> >
> >>Can anybody help on this one? It's an M8190 KDJ11-B, again with no
> >>additional revision ID _anywhere_ on the board.

> >They're all the same, all QBus. Well, all the same except for
> >ASICs, and ROMs. The ones used in 11/84 machines go in a QBus
> >backplane, with PMI memory in front and a KT84 QBus-to-Unibus
> >behind.
> >
> >Simplifying slightly, the earliest J-11 chips would not reliably run
> >faster than 15MHz, and were used for 11/73s. Later ones ran at
> >and were used for 11/73s, 11/83s, and 11/84s. Some ASICs did not
> >correctly with the FPU accelerator, later ones did. Any set of ROMs
> >from the series will work in any of the boards, but later ones
> >more boot devices and present different menus.

> Jerome Fine replies:
> Actually, there really are two different board numbers
> even though the module is named as a KDJ11-Bx. The
> M8190-BA,B,C has 3 versions and are all officially
> call PDP-11/73 with probably most (maybe all) running
> at 15 MHz and the different versions being for the FPU.

> I may not remember correctly, but I seem to think that
> the 83/84 board, the KDJ11-BF which is both an PDP-11/83
> and the 11/84 has a different module number.

No. There's one board, with one number. Those sold as 11/73 had
processors running at 15MHz and didn't have the FPU fitted as standard,
those sold as 11/83 or 11/84 had faster processors (or at least a
faster clock) and did have an FPU. The boards themselves are the same.
 You might be thinking of the M8192 KDJ11-A which is a smaller board
used mainly in OEM equipment and for 11/23 upgrades, or perhaps of the
11/53 or 11/93 boards.

*Originally* DEC used the -BC and -BB suffixes in the *name* (as in
KDJ11-BC) to denote those M8190s with DCJ-11 CPU chips that were/not
capable of being upgraded with an FPU, and used the -BF suffix to
denote one that was factory-fitted -- which originally they only did
for 11/83s, which ran at 18MHz.

On some boards, those suffixes are translated into suffixes to the
M8190 module number. M8190-AB is KDJ11-BB and M8190-AE is KDJ11-BF.
 However, ones with no FPU but capable of being upgraded had no suffix,
so plain M8190 could be KDJ11-BC. Unfortunately for people trying to
follow this scheme, boards were produced with no marked suffix, but
running at 18MHz and with an FPU (my 11/83 is like that).

Those suffixes don't reliably denote the presence, absence, or
capability of having an FPU. That's determined by the ASICs, or
perhaps, from something I read once, mainly by the revision of the
DCJ-11 chip itself.

Further confusion arises because different versions were sold with
different ROM sets, but over the years people upgraded the ROMs to get
additional bootstrap or diagnostic capabilities, and sometimes added
the FPU to 11/73s. I've even heard of people changing the processor,
either to fix the FPU problem or uprate the clock. And to add insult
to injury, people have moved boards between cabinets or reordered the
memory and CPU without changing the badges. A BA23 "storage heater"
might have had an 11/83 that got moved to a BA123 "hostess trolley"
with an 11/73 badge.

> What is not well known (or at least not in the beginning)
> was that ALL of the KDJ11-Bx boards could run with or
> without PMI memory. In addition, even if PMI memory was
> used, if located BELOW the CPU board, it was used as
> ordinary memory, if used ABOVE the CPU board, it was
> used as PMI memory.

Indeed. Diagnostics and operating systems distinguish 11/73 from 11/83
by looking at a bit that relates to PMI memory.

> MOST of the increase in speed for a PDP-11/83
> was due to the PMI memory, not the shift to 18 MHz.

Well, about half, depending on the makeup of the benchmark used. I
tried the permutations once, by re-ordering boards and changing the
crystals (what I was really trying to do was see how fast I could get
one to go: 20MHz with the chips I had).

Executive summary: 11/73s and 11/83s use the same board (except for
dual-height KDJ11-A OEMs and upgrades to 11/23 systems). Original
11/73s ran at 15MHz and may or may not have an FPU. Original 11/83s
run at 18MHz and have an FPU (except, I'm told, for a tiny number or
early units). What makes an OS think the processor is, depends on
whether you use PMI memory in front of the processor (11/83) or QBus
memory behind it (11/73), and that also affects the system throughput,
to at least the same extent as the clock speed. What determines
whether the clock can run at 15MHz or 18MHz (or higher), and whether
the FPU can be added, is the CPU/ASIC chip revision, not the board.

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Sun Feb 06 2005 - 06:32:04 GMT

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