Software for small-memory PDP-11s?

Josh Dersch derschjo at
Fri Nov 13 17:43:36 CST 2015

On Fri, Nov 13, 2015 at 2:52 PM, js at <js at> wrote:

> On 11/13/2015 5:45 PM, Josh Dersch wrote:
>> Hey all --
>> Now that I have my PDP-11/05 running nicely,
> What did you end up doing to arrive at that functionality?  Did I miss
> some emails?

Total issues over the past year or so were:
- Power supply needed some work.
- CPU non-functional: traced down to a pair of microcode PROMs with bitrot;
regenerated PROM images from the original service manual scans on
Bitsavers.  (Ugh)
- Dead 128 word region in 8KW core plane:  Traced down to a broken wire on
the core mat; unfixable (by me at any rate).  Lucked into a cheap (and
fortunately working!) replacement on eBay a couple of weeks back.
- Bad Boxer fan (completely dead, likely the cause of the PROM failures due
to overheating many years back...)
- Failing diagnostics: traced down to operator error on my part
(misjumpered SLU interrupt vector).

> I'm curious what others are
>> running on small systems like this -- until this point I've only played
>> with larger (i.e. at least 28KW memory) systems.  I have only 8KW of
>> memory
>> (with no viable options for expansion)
> Can't MOS memory be put on the Unibus in an expansion chassis?

Yes.  "viable" in this case translates to "I have the parts on hand, or
parts are easy to come by."

- Josh

> and there's not much out there that
>> I've found.  There's paper-tape BASIC (which is always fun) and FOCAL, and
>> PTS-11 ( which is pretty
>> cool
>> if a bit cumbersome.  Any other suggestions?
>> I'm also curious if any version of RT-11 that supports the TU58 could be
>> made to run on this system -- I have two SLUs in the system so in theory I
>> can boot from an emulated TU58. However RT-11 4.0's SYSGEN manuals suggest
>> that 12KW is the minimum supported (and experimentation bears this out)
>> and
>> I can't find much in the way of manuals for RT-11 V3B -- which I believe
>> is
>> the earliest version with TU58 support.  (V3B seems to be different enough
>> from later versions that I'm not quite sure how the SYSGEN process works.)
>> Thanks as always,
>> Josh

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