[TUHS] quick question on PDP-11 addressing

[segaloco via TUHS]

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.