[TUHS] update pdp11 system five?

[Ron Natalie via TUHS]

  I know for the BSD-ish networking on the PDP-11, it took one of the 8 
kernel data segments to map mbufs.   The top one is already reserved for 
the user struct/stack.
The problem was that we were running out of address space even before 
putting TCP/IP into the kernel.   We had to overlay the text pages.     
This is workable on the split I/D (23, 24, 44,45,55,70) but it killed 
off the idea of using those without it (11/34, 40, 60) for running 
networked UNIX.

This was about the time I started recycling the PDP-11s into internet 
routers running the BRL-GATEWAY software.   Eventually, even the 11-70’s 
succumbed to this.   It was overkill, but I had them lying around.   I 
also recycled one into being a control processor for the Denelcor HEP 
I/O system.
The BRL-GATEWAY was my own invention running on a little pidgeon 
operating system called LOS (the little operating system).    I did this 
when the MIT C Gateway lacked the features we needed and Noel Chiappa 
was at the time exiled to the Bahamas or something.

-Ron

I did get the BRL UNIX system (thanks guys) from McKusick’s repository 
for my PiDP-11 sitting on my desk.   I suspect the LOS operating system 
and the accompanying router code has been lost to antiquity.




------ Original Message ------
>From "Larry McVoy via TUHS" <tuhs at tuhs.org>
To arnold at skeeve.com
Cc tuhs at tuhs.org
Date 12/17/2025 10:49:17 AM
Subject [TUHS] Re: update pdp11 system five?

>On Wed, Dec 17, 2025 at 08:41:05AM -0700, Arnold Robbins via TUHS wrote:
>>  IIRC the last official System V release that ran on the PDP-11 was
>>  S5R2, but I don't remember for sure.
>>
>>  S5R3 had STREAMS networking.
>
>I don't believe that's correct.  SCO's S5R3 did not, I had to port it.
>
>>  S5R4 had real demand paged virtual memory and also, I think, socket support.
>>
>>  Lack of address space will definitely be an issue; you'll have to look
>>  at overlays or some such, which I think 2.11 BSD does.
>>
>>  But I bet you'll have fun! :-)
>>
>>  Arnold
>>
>>  Jacob Ritorto via TUHS <tuhs at tuhs.org> wrote:
>>
>>  > pdp11s are getting so popular these days that now seems a great time to perform the stunt of running SYSV well on them.  Seems pretty normal to the adepts on the list who were there when it originally happened, but it???s kind of a niche mind-blow to newcomers that a PDP could run SYSV.
>>  >
>>  > But currently I think it???s missing networking.
>>  >
>>  > So a couple questions:
>>  > Is it possible to build newer SYSV releases to run on pdp11?  Like specifically SVr4?
>>  > If not, is this feasible to achieve and would anyone be interested in a project to make that happen?
>>  > If that can happen, the stock SVr4 networking code build might be a breeze.
>>  >
>>  > Apologies in advance if this has already been broached and completed and/or if this is a fool???s errand due to size constraints.  And yes of course the easy thing to do is just run v6 or BSD.  But then we miss out on the mind-blowing facet :)
>>  >
>>  > thx
>>  > jake
>
>--
>---
>Larry McVoy           Retired to fishing          http://www.mcvoy.com/lm/boat