[TUHS] First Unix that could run on a PDP-11 with QBUS

Dave Horsfall dave at horsfall.org
Tue Jul 29 08:23:12 AEST 2014

On Mon, 28 Jul 2014, Noel Chiappa wrote:

> > I recall that there were other differences as well, but only minor. In 
> > my paper in AUUGN titled "Unix on the LSI-11/23" it will reveal all 
> > about porting V6 to the thing.
> I did a google for that, but couldn't find it. Is it available anywhere 
> online? (I'd love to read it.) I seem to recall vaguely that AUUGN stuff 
> were online, but if so, I'm not sure why the search didn't turn it up.

There was a project a few years ago to scan all issues of AUUGN 
(Australian Unix Users Group Newsletter); the last I heard was that all 
issues had been obtained, and handed over to some Google mob for 
archiving.  Apparently the scanning process is destructive but makes for 
an ideal copy for as many as you like.  The originals, being up to 40 
years or so old, would have been in bad shape anyway.

A search for "auugn" reveals a few pointers, but AUUG itself dissolved a 
few years ago because we had achieved our purpose i.e. bring Unix to the 
mass market in Australia (its competition at the time was RSTS, RSX, and 
PICK of all things).  Guess which one survived?  Concurrent CP/M never 
really had a hold, MS-DOS thankfully died (I was still using CP/M at the 
time; heck, I even had UUCP on it, which was pretty impressive considering 
that the Microbee didn't have a serial port), and I predict that Windoze 
will go the way of the Irish potato crop and for the same reason.

Warren may know more about the archived issues.

> > I vaguely remember that the LTC had to be disabled during the boot 
> > process, for example, with an external switch.
> I think you might be right, which means the simulated 11/23 I tested on 
> wasn't quite right - but keep reading!

It was hilarious, in a morbid sort of way.  I cottoned on when the 
bootstrap process crapped itself for no apparent reason (it got 
interrupted when no ISR was in place), and we'd occasionally forget to 
enable it...

> I remember being worried about this when I started doing the V6 11/23 
> version a couple of months back, because I remembered the 11/03's didn't 
> have a programmable clock, just a switch. So I was reading through the 
> 11/23 documentation (I had used 11/23s, but on this point my memory had 
> faded), trying to see if they too did not have a programmable clock.
> As best I can currently make out, the answer is 'yes/no, depending on 
> the exact model'! E.g. the 11/23-PLUS _does_ seem to have a programmable 
> clock (see pg. 610 of the 1982 edition of "microcomputers and 
> memories"), but the base 11/23 _apparently_ does not.

I never saw the -PLUS, so I can't help you there, and my shelf of DEC and 
Unix etc manuals disappeared during several moves.

> Anyway, the simulated 11/23 (on Ersatz11) does have the LTC (I just 
> checked, and 'lks' contains '0177546', so it thinks it has one :-).

Quite likely.  I came up with a battery of tests at boot time, in order to 
determine just what sort of a model it was e.g. did it have the SLR and so 
on.  Same thing for illegal instructions, such as floating point.  We had 
/40s all over the place (some dedicated ones had no MMU, and ran a custom 
program to talk 200-UT to a remote Cyber), two or three /70s (I had no 
responsibility for those, but we shared code a lot), a /60 (interesting 
box), and a sprinkling of /23s.

> But this will be easy to code around; if no link clock is found (in 
> main.c), I'd probably set 'lks' to point somewhere harmless (054, say - 
> I'm using 050/052 to hold the pointer to the CSW, and the software CSW 
> if there isn't a hardware one). That way I can limit the changes to be 
> in main.c, I won't have to futz with clock.c too.

Speaking of the CSW, we came up with some amusing idle patterns.  The 
boxes with the octal display displayed rotating 1s (I had to determine 
whether it had an octal display or a real one somehow; I've long since 

> PS: On at least the 11/40 (and maybe the /45 too), the line clock was an 
> option! It was a single-height card, IIRC.

Yeah; the aforementioned low-end /40s had quite an impressive program that 
scheduled by the use of co-routines (no LTC either).  It emulated the CDC 
Remote Batch Station (we briefly had one of those too; it was S L O W).

Fun days!

-- Dave

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