The pdp-12 was a 12-bit machine built in the early 1970s as a successor
to the LINC-8 machine. For those who have never seen one, this is a LINC-8:
The original LINC was a special-purpose Laboratory INstrumentation Computer,
started at Lincoln labs, then moved to MIT. Built using DEC components, then
built and sold by DEC themselves. The LINC-8 was the first concept of a CPU
which could run both LINC and pdp-8 instructions, in one chassis. The pdp-12
was the final expression of this idea.
It was a special-purpose machine built to cater for the needs of laboratory
experiment control and data acquisition, being plentifully equipped with
options for a/d, d/a and relay control interfaces. It featured a remarkable
cpu which could operate in two modes - LINC compatible and pdp-8 compatible
- and switch between them whilst running, allowing pdp-8 and LINC instructions
to be mixed!
This particular system (which was in use until I collected it in 1993)
came from the Burden Neurological Institute in Bristol, UK, where it was
used to record and analyse the results of neurological experiments. It
came with another pdp-12, which I sold to a British DEC dealer who wanted
it for his personal collection! At the time I removed it, there were still
two other pdp-12s on site there, one complete and in use, the other dismantled
for spares. One machine remained in intermittant use until at least 2001!
I had been promised the remaining equipment when it was finally surplus
to requirements, and telephoned the insititute every few months, always
getting the reply ' it will be a few more months at least'... then came
the fatefull day in early 2002 when I called anf heard 'oh sorry we forgot
about you - we got rid of it all a couple of months ago, it all went to
an old computer enthusiast who asked us for it!' Grrrrrrrrrrrrrr.
It came with a fair collection of software on LINCtape, and runs the DIAL
It's quite a highly expanded system, with 3 linctape units (identical
to dectape but incompatible - the motors are wired to run the opposite
way!), an FPU, an RK05 and controller (the controller is a small Omnibus
chassis with an RK8E in it, plus the boards to interface it to the pdp-12
bus!), some custom experiment control hardware, and a 3rd party Fabritek
32 kword core box (the orange box in the photo).
Whilst I'm very fond of it - the pdp-12 is probably my favourite of all
the pdp systems - this particular pdp-12 is one I'm not very happy with. It's been quite heavily
modified - a non-DEC power control system, backplane changes, a kludge
board to make the console interface RS232 instead of 20ma, non-DEC memory
expansion... and it wasn't in good physical condition when I got it. All
of which I dislike. I'd be much happier with a plain old unmodified basic
pdp-12 with a LINCtape or two, like this:
The current status of the system is 'faulty' - it worked ok when I got
it and for some time afterwards, but then it went down bit by bit... first
the terminal control, then the LINCtape control, then it failed totally,
getting hung with the run light on if you use any of the major console
switches - exam, dep etc. Probably something fundamental like missing volts
to memory... haven't had time to troubleshoot yet.
Troubleshooting is fun... the LINCtape controller is a complex state machine
of some notoriety, the cpu & backplane are a rat's nest...
A very comprehensive front panel... most unfortunately wrecked. It was
shattered when I got the system :-(
I have a complete set of manuals and prints for this system and a good
set of s/w on LINCtape. I need a spare front panel - the printed screen,
not the lights and switches - as it was damaged before I got the system.
Even the loan of an undamaged one to make a copy would be helpful.
Some useful pdp-12 links (LINCs?):
http://www.faqs.org/faqs/dec-faq/pdp8/section-7.html LINC and pdp-12 FAQ
http://www.parse.com/~museum/pdp12/index.html Robert Krten has one
http://www.cca.org/tech/rcs/pdp12.html RCSRI have *three* pdp-12s!
http://www.spies.com/~aek/pdf/dec/pdp12/ Al Kossow's invaluable collection of pdp-12 manuals (I contributed the FPP12 printset :-)