[TUHS] update pdp11 system five?

[Warner Losh via TUHS]

On Wed, Dec 17, 2025 at 8:22 AM 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?
>

Nope. The only extant version of system V that runs on the PDP-11 is r1.


> If not, is this feasible to achieve and would anyone be interested in a
> project to make that happen?
>

No. It's too big and requires demand paging. There's some nuance in this
answer, but nobody has ported the R1 support code forward and the time I
looked at it suggested there'd be a lot of work.

If that can happen, the stock SVr4 networking code build might be a breeze.
>

Not really. If you look at 2.11BSD you'll see that to put the BSD
Networking stack into it had to use both separate I&D space, but also
needed to use one of the 'extra' priv levels to effectively run most of the
BSD stack in an extra privileged process.

Warner


> 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