>Pete Turnbull wrote:
> No, not true. There are both dual and quad 11/73 (the quad being an
> 11/73-plus). The 11/73 was 15MHz, the 11/83 was always sold as 18MHz.
Jerome Fine replies:
While I have heard of a PDP-11/23 PLUS, I don't think
that "PLUS" was ever applied to the PDP-11/73 boards.
>From what I understand, for the PDP-11/23 boards, the
"PLUS" could mean either the ability to address all 4 MBytes
of memory with the dual M8186 boards (I understand that
the original M8186 boards were able to address only 256
KBytes) or that the quad M8189 board was being used.
As for the PDP-11/73 boards, I had heard that some
did have the 18 Mhz crystal, but that might also have
been done privately. Megan Gentry just mentioned
that she changed the crystal on her PDP-11/83 board
to 20 MHz and it ran correctly.
> So does the 11/73, though it's different.
This answer was with respect to the boot ROMs. I have
both a KDJ11-BB (M8190-AB) and a KDJ11-BF
(M8190-AE). Aside from the 15 MHz vs the 18 MHz
crystal, the fact that the latter also had the FPU chip
was standard with the KDJ11-BF. But the rev number
of the J11 chip on the KDJ11-AB is 04 and the EPROMs
are version 395E5 / 396E5 which can also be the EPROMs
for the KDJ11-BF. However, I understand that the J11
rev number when an 18 MHz crystal is being used must
be at least 08 and maybe 09.
So the dialogue for the PDP-11/73 and the PDP-11/83 can
be identical - it just depends on which version of the
EPROMs is being used.
> Source: personal experience of field servicing all of the above types,
> plus the Micro-PDP-11 Maintenance manual.
I agree, however, that the early EPROMs would not have
been used with a KDJ11-AE board, but the EPROMs
on an early KDJ11-AB could easily have been updated
along with the J11 rev number.
All this discussion seems to point out that the PDP-11/73,
PDP-11/83 and PDP-11/93 boards were not identical
nor did they use the same J11 CPU chip all the time, although
the last 09 rev CPU chip that was used with the PDP-11/93
would probably work with all of the others, just NOT the
other way around with the early 04 rev CPU chips.
The really sad part of the whole PDP-11 situation was that
DEC upper management decided early in the 1980s to
attempt to kill the PDP-11 as far as can be understood
from the decisions that were made. From my perspective,
IF DEC had decided to split into two completely separate
and independent companies in 1985 - PDP-11 & VAX,
we might still be seeing both being built along with the
Alpha. The competition from a strong PDP-11 (even
though the target market was different by 1990) might
have been sufficient to keep both the PDP-11 and the
VAX alive since both companies might have actually
started to advertise to build market share. And with
the advent of the Alpha and another separate company,
that market might also have needed advertising.
While a 16 bit (64 KByte) address space is extremely
limiting, for programs overlays can normally (I agree NOT
always) substitute. For DATA, FORTRAN was able to
solve that problem with VIRTUAL. For the target market
of the PDP-11 where they are still being used, such a
CPU is still satisfactory. And with Ersatz-11 showing
that a much faster CPU (50 times the speed of the 11/93)
keeps an existing system competitive, it would have been
reasonable to assume that if the Alpha could manage to
switch to a PCI bus, then likewise it seems very possible
to me that the PDP-11 could have done so as well.
>From that point, a 24 bit bus with 16 MBytes and later
even a 32 bit bus could have kept the PDP-11 somewhat
competitive if there seemed to be sufficient interest.
ALL GONE!!!!!!!!
Sincerely yours,
Jerome Fine
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Received on Sun Dec 14 2003 - 16:47:17 GMT