[TUHS] quick question on PDP-11 addressing

[ron minnich via TUHS]

related question, when people started getting their VAXes, what was the
smallest configuration that ran Unix?

On Mon, May 4, 2026 at 3:07 AM Arnold Robbins via TUHS <tuhs at tuhs.org>
wrote:

> segaloco via TUHS <tuhs at tuhs.org> wrote:
>
> > On Monday, May 4th, 2026 at 00:51, Arnold Robbins via TUHS <
> tuhs at tuhs.org> wrote:
> >
> > > Jonathan Gray via TUHS <tuhs at tuhs.org> wrote:
> > >
> > > > On Mon, May 04, 2026 at 02:19:59AM -0400, Phil Budne via TUHS wrote:
> > > > > I wrote:
> > > > > > CB (Columbus Bell) Unix, and SVR1 ran on 11's and supported
> shared
> > > > > > memory segments.
> > > > >
> > > > > The sysv_pdp11.tgz I just found has has a library shmsys.c which
> > > > > indicates SHMSYS was syscall 52, but it's a "nosys" entry in
> sysent.c
> > > > > AND I've yet to spot the kernel support in the available CB Unix
> > > > > listings...
> > > >
> > > > You may be looking for MAUS?
> > > >
> > > >
> https://www.tuhs.org/Archive/Distributions/USDL/CB_Unix/man/man2/maus.2.pdf
> > > >
> > > > maus.c cbunix4.pdf pp 64-66
> > > > sysent.c cbunix6.pdf pp 50-52
> > > >
> > > >   1, &maus,                       /* 58 = set up MAUS segment reg */
> > >
> > > The UNIX 4.0 release notes that Matt sent out a little while ago
> > > mentions that on the PDP-11 MAUS is supported instead of the
> > > shared memory sys calls.  FWIW.
> > >
> > > Arnold
> > >
> >
> > MAUS AFAIK starts as a CB phenomenon in the late 70s, very PDP-11
> > specific.  Since shm is expected in future non-PDP-11 UNIX, a separate,
> > more portable solution was developed (I don't know the internal name)
> > which supports all the future platforms, but isn't workable in PDP-11
> > UNIX.   Between this and other factors, SVR2 is the last USG UNIX to
> touch
> > the PDP-11 as far as prevailing literature is concerned.  For instance, I
> > have the SVR2 System Release Description and it still mentions PDP-11/70
> > compatibility.  That said, machid(1) as of SVR4 manuals lists pdp11
> > as a reportable target.  I've never confirmed whether this is simply a
> > matter of aged documentation or if somewhere deep inside AT&T they kept
> > SysV going on PDP-11 past SVR2.  For the record, 3B20 and 3B21 UNIX was
> > supported long after SysV went the SCO route in the from of UNIX/RTR.
> > That's only to point out that some of the 70s UNIX platforms do have
> > continuity to the 90s, 2000s, and beyond, so who knows, maybe somewhere
> > in BTL/Lucent there was some stripped out SVR4 running on a PDP-11/70.
> > Last confirmed date of USG UNIX issued for a PDP-11 falls in 1984 though.
> > I have a Lucent training document on C in shipment currently, I'll see
> > soon if it lends any credence to late-era PDP-11 support in the USG
> > or BTL streams.  Given BTL moving to VAX-11 in the early 80s though,
> > anything post-that e.g. Lucent it's may yield nothing useful in the
> > PDP-11 longevity question.
> >
> > - Matt G.
>
> It is super unlikely that anything past SVR2 ran on the PDP-11. Demand
> paging was introduced sometime in the SVR3 period, along with STREAMS
> networking, the filesystem switch and RFS, and SVR4 was architectually
> very much like SunOS, with demand paging, a vnode-based filesystem
> architecture, both traditional and BSD fast filesystems, and with socket
> and STREAMS networking, NFS and I think even RFS.
>
> WWWWAAAAYYY too much to shoe-horn into an -11.
>
> The porting platform changed over time also, from -11 to Vax to 386 and
> 3Bxx,
> with older ones being dropped along the way.
>
> Arnold
>