[TUHS] quick question on PDP-11 addressing

[Arnold Robbins via TUHS]

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