PDP-11/05 returns to life

[Ethan Dicks]

On Tue, Jan 6, 2009 at 3:19 PM, Tobias Russell <toby at coreware.co.uk> wrote:
> I managed to coax my PDP-11/05 back into life today and ran a few simple
> programs on it successfully.
>
> As a result a few questions for the experts out there:
>
> 1. To get it up and running I had to replace its two fans both of which
> had failed which I did by scavenging another 11/05 chassis I have.
>
> Does anyone have any tips on reviving failed fans?

Just what you've done... clean and lube (WD-40 is *not* lubricant!)
If they really won't spin and they are oddball fans, you might need
exact replacements (ISTR the 11/40 or 11/45 has that problem), but if
you find a modern fan that's the same size and voltage, you are
probably OK.


> ... if recovery is impossible can anyone suggest suitable replacements? The
> current ones are labelled Super-Boxers

I think you might still be able to get fans like that, but I haven't
tried in at least 5 years.

> 2. Is there a chasing lights program I can run on the 11/05? Would be
> nice to see it visibly doing something

From: <http://www.psych.usyd.edu.au/pdp-11/11_40.html>

Toggle in the following program and start at 001000. Note that the RUN
light will go out!

	Location	Contents	Opcode		Comment
	001000		012700		mov #1,r0	Load 1 into R0
	001002		000001
	001004		006100		rol r0		Rotate R0 left
	001006		000005		reset		Initialise bus (70ms)
	001010		000775		br .-4		Loop back to 'rol r0'

I do not know if this will work on an 11/05 because of the 'reset'
instruction, but it's a start.  You could replace the reset
instruction with an inner loop on r1 without too much difficulty if
this won't work on your machine.

> 3. At the moment the machine has 16KW of core (2 x 8KW planes). This
> together with the CPU fills all but the last slot on the Unibus (its a
> 5inch box so only 9 slots). I'd like to fit a DL11 so that I have some
> serial comms and ideally an RX11 as well so I can hook up my RX01 drives
> and boot RT-11. Can I make use of the 9th slot or does this have a
> special purpose? There is a lot of wire wrap going to slot 9 so I'm
> guessing its not suitable.

My memory is that you can use the 9th slot for an SPC (small
peripheral controller), but check the 11/05 handbook to be certain.
IIRC, The RX11 and DL11 do not need NPR (but the RX211 might), but
look those up in a mid-1970s handbook to be certain.

> 4. What versions of RT-11 is suitable for an 11/05 and what is the
> minimum memory to run it?

I would think that RT-11 v4.0 would work nicely on an 11/05.  I'm
pretty sure even the newer stuff will work, but since you don't care
about MSCP support or other modern niceties, it may not be a big win
for you.  Games and such, at least the ones I know of, should run on
V4 and V5, as long as you have enough core for the app itself.  Don't
expect to run ADVENT without a full boat of memory, but there are
plenty of smaller apps out there.

-ethan