[TUHS] shared memory on Unix

Steve Johnson scj at yaccman.com
Thu Feb 2 05:11:35 AEST 2017

I can't speak for the dates, but Ken did a hack to the OS to interface
with his Chess machine.  Recall that all the I/O on the PDP-11 was
memory mapped, so as I recall he simply mapped a piece of kernel
memory into user space.  Was never privvy to the details.

I do remember a conversation with Dennis about semaphores, though. 
He mentioned that no less than five groups inside of Bell Labs had
hacked semaphores into the kernel.  Each group did it differently. 
He thought they were all a bad idea -- his argument was, "what do you
do if a process sets a semaphore and then dies?  It's pretty clear
that either releasing the semaphore or leaving it set would be
catastrophic in some cases."  

(Of course there were other similar problems, such as a process
closing its files and dying, and then the kernel discovering that the
disc was full.   Luckily, these days, the disc rarely gets full...)

Also, a comment from my own experience with AT&T marketing.  When I
was responsible for the System V languages in Summit, I was told that
a marketing group was staffed and that there was a person in charge of
marketing the language products (at the time, C, Cfront (becoming
C++), Fortran, Pascal, and Ada).  I set up a monthly meeting with
this person.  The meetings went on for over a year, but _I NEVER MET
WITH THE SAME PERSON TWICE!_   It seemed that the only thing the
marketing group knew how to do was reorganize the marketing group...

At the time, a lot of people buying VAXes were running VMS because its
FORTRAN was far better than UNIX F77 -- in particular, it had an
optimizer.  I started a project to build an optimizer for FORTRAN,
and staffed it with several very good people.  Every six weeks there
would be an attempt to kill the project.  Each time I'd repeat the
argument for doing it, and it would be saved.  We almost started to
put these attempts to kill it on the calendar.  At no time did I get
any feedback, positive or negative, from AT&T marketing.   When I
left AT&T in early 1986, the optimizer, by now almost complete, was
immediately killed again.    I was later told by one of my former
team members that it was revived several months later and finally made
it out.  And that the next year it was the best-selling add-on to
System V.


----- Original Message -----
From: arnold at skeeve.com
To:<schily at schily.net>, <clemc at ccc.com>
Cc:<tuhs at minnie.tuhs.org>
Sent:Wed, 01 Feb 2017 11:33:05 -0700
Subject:Re: [TUHS] shared memory on Unix

 Clem Cole <clemc at ccc.com> wrote:

 > Note that AT&T Marketing renames PWB 3.0 -- System III thinking
 > "Programmer's Workbench" would be a bad name to sell against IBM,
and this
 > it the first non-research system for License outside of the the
labs. If
 > you look at the documentation set, et al - it all says PWB 3.0 on
the cover
 > and throughout Also, the BSD vs AT&T wars basically start around
 > time....
 > Roll the clock forward and here is an new problem the PWB 4.0
moniker was
 > used internally, but AT&T marketing want to get rid of the PWB term
- so
 > the decree comes down the next release is to be called System V.

 Sort of. I did some contract work for Southern Bell circa 1983. They
 were still part of the Bell System then. I worked on a PDP-11 running
 Unix 4.0. At the time, the policy was to release externally one
 behind what was being run internally, so System III was released to
 world while the Bell System was using Unix 4.0. I still have the
 I'm pretty sure "PWB" and "Programmer's Workbench" are not on the
 it was just called "UNIX".

 As UNIX 5.0 was approaching, someone decided that to be one release
 behind on the outside was dumb, thus the jump from System III to
System V.

 The doc I have describes UNIX as an operating system for the PDP-11,
 the VAX 11/780 *and* the IBM S/370 series of systems and the source
 code directory had the machine dependent bits for the IBM. Too bad
 that stuff never made it out.

 It's too bad that all I have is just the paper, but that's all I
 could get.

 That was a fun job, I learned a lot. Over lunch every day I read a
 more pages of the manual, basically reading it from cover to cover
 by the time I was done. What a great way to learn the system!


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