On Apr 13, 2013, at 7:13 PM, William Barnett-Lewis wrote:
I've been learning about the PDP-11 lately thanks
to the wonder that
is Simh, running various software on it and generally having fun. I
don't have any purpose other than that at this time. I've been running
everything I can get my hands on though I find, given my background,
tastes and biases, that it's usually either Unix Version 7 or,
especially, 2.11BSD that I'm firing up and exploring rather than, say
the more DEC traditional RSTS/E.
That said, I've been wondering what would be different (aside from
noise & heat ;) about running 2.11BSD on hardware rather than in Simh
on my increasingly decrepit Dell C640 running Xubuntu. Logically I
should spend the money on a new intel based laptop but what's the fun
It'll be a lot slower than SIMH. Between the much slower
disk access speeds of vintage hardware and the fact that
even on a low-end modern Intel microprocessor the emulation
is still many times faster, it will feel noticeably slower.
For example, an RSX-11M SYSGEN takes about a minute and a
half on my Core 2 laptop from 2008, while it takes about
three hours on my 11/23 running off a reasonably fast SCSI
But it's way more fun. :-)
But then that turns on the question - is there even a
that can run 2.11BSD? I don't need a speed demon but how small is too
small vs big enough?
For various values of "cheap", yes. Be prepared to buy
parts piecemeal as you find them at good prices on eBay;
you can fool around with banging stuff in over microcode
with just a CPU and some RAM (and, obviously, a backplane
and a power supply, though you can use a PC power supply
if you can hook it up to a backplane). If you have a
serial line, you can hook it up to a DECTape emulator on
a PC for block-based storage space to boot, say, RT11.
Let me see if I understand correctly what I would
A BA23 or BA123 chassis. Would others work as well?
Yes. The BA11-N, -M and -S chassis are also quite
suitable boxes. You don't necessarily need the chassis,
actually; for a long time, my 11/23 was running in an
open H9270 backplane (the 4-slot serpentine one from the
BA11-M) hooked up to a PC power supply with some fans
from Target to make sure I had adequate airflow.
skimp on the airflow.
A simple review of QBUS chassis that covers most of the
relevant details is here:
A CPU with separate I/D space. 11/23, 11/53, 11/73,
11/83 or 11/93
would work with the Q-bus chassis above.
Yes, as well as the LSI-11 and /03, but the /23 and below
do not support separate I/D space. You need a KDJ11 CPU
for that, which means a /53, /73, /83 or /93. You can
often find KDJ11 boards reasonably priced on eBay (I know
JT Computers, username conflansrd, has both the -A
version (/73, dual-width card) and -B version (/83, quad-
width with PMI capability) for $120).
I recall that there are KDJ11-B boards that are marked
as 11/73 boards; those can use PMI, but I seem to recall
that the difference is that they couldn't use the FPA
(floating point accelerator).
Try to get a -B board of whatever you get; I like my
KDF11-B quite a bit because it has the boot ROM and
console serial line (plus a bonus serial line) built
in. The KDJ11-B has that as well. You can run 2.9
BSD on a KDF11.
1mb to 4mb memory, 1mb is absolute minimum for 2.11
BSD & 4mb is
For DEC OSes, you can get away with somewhat less. When
you're getting RAM, make sure it's the right kind;
MSV11-J RAM is PMI memory for the /83 and /93, while
MSV11-P and -Q (and some others) are regular QBUS RAM.
The -Q (-QA, -QB and -QC, which are 1, 2 and 4 MB quad-
width boards) are block mode DMA capable, which is nice
if you have I/O devices that can take advantage of that.
Disk controller - though more expensive, sanity really
says I should
find a SCSI controller like RQZX1, Emulex UC-7 or CMD CQD-220. I have
old SCSI disks; ESDI & the like? Not so much ...
A RQDX3 & RX50 or TQK70 & TK70 would probably be in the 'nice to
have' category as well.
A SCSI card is great. If you find one at a good price,
get it. I love my CQD-220. If you get one, NEVER set
the number of tapes and disks to 0, or you'll brick
your card. I have a ROM fix for that, but it's a pain.
DELQA ethernet controller
Would this work? What are the going rates for hobbyists (rather than
resellers to those with production equipment)? Are there any, hmm,
less expensive bits here or there?
Most of my cards (including CPU, RAM, DELQA, CQD-220
and a few others) came in around 100-150. Sometimes
I was lucky and got them a bit cheaper. This was
almost all off eBay, though; if you know the right
people (I didn't when I started collecting), you
can get away much cheaper.
This is mostly a thought experiment as I don't
really have the
disposable cash right now for the various parts right now. OTOH, I
find the process of learning more about the hardware, what would be
required and how it functions, to give me a better understanding of
what I'm doing with the emulator.
Thanks to all here (the 11/23 thread has been of great value to me)
and to bitsavers ;) and all the other fun resources out there.
Have fun, that's the important part! Get the bare
minimum of useful hardware first so you can play
around with ODT and keying in programs; you can
build it up over time without stressing your wallet
out too much.