[ih] BBN C-series computers

[James J Dempsey]

I used the C/70 as a user -- I was not involved in C-Machine development.
However, I feel I can answer some of these questions, so I'll give it a go.
I read internet-history in digest mode; it's highly possible someone more
authoritative than me will have already answered these questions.

David Walden <dave.walden.family at gmail.com> wrote:

> I was not close to the C/70 project so I don't know.  
> We can find the right person to answer questions with a question to the ex-BBN list.  In the meantime, I will look in the list of BBN reports.
> 
> On October 23, 2017, at 9:17 PM, Bernie Cosell <bernie at fantasyfarm.com> wrote:
> 
> > - Can you confirm that the C/70 indeed ran the TCP/IP stack?
> 
> I don't know.  I expect it did

The C/70 (as well as the C/60) definitely did have a TCP/IP stack.  One of
the first uses of the C/70 was to build and run the NU Network Monitoring
system.  When I arrived at BBN in the Summer of 1981, we were already on
track to transition ARPANET to TCP/IP, which as we know eventually happened
on 1 Jan 1983.

It was important that NU be able to monitor the ARPANET at that point
because the TENEX-based U program (which previously monitored and controlled
ARPANET) could not handle TCP.  My memory is that some people thought NU was
not up to the task by this point, but it was certainly moot since many
aspects of the U program would not work after the transition.

> > - The advert says the C/60 was running V7 Unix, I assume this was true
> > of the C/70 as well? Before now, I did not realise that the TCP/IP stack
> > integrated with V7 as well.
> 
> That was the version of unix we had the sources for.  

Yes - I understand that this was a financial issue.  BBN had a V7 source
license.  If we wanted a newer UNIX license (System III was announced in
1981), the price for a source license was very expensive.

And really, most developers didn't want System III at that time anyway.
What we really wanted was BSD and the BSD license gave us access to those
sources as well.  As a result, BBN-UNIX (as it was called) had many BSDisms
and looked (in many, but not all ways) a lot like BSD.  Certainly, the csh
shell was there, though I'm pretty certain the TCP stack was BBN's, not BSDs.

I still have a button from a conference or show that says "I <heart>
BBN-UNIX, supported by BBN Computer".  I was told that the big deal was that
BBN actually had commercial support for UNIX which was rare or non-existent
for a computer manufacturer at the time.

You can see that button (and some others) here: 
http://serenity.jjd.com/Images/bbn-buttons.jpg

> > - Would you at this remove still remember the main features of the C/70
> > MMU? This detail is relevant to me as it has a connection to the
> > evolution of network buffer management in Unix, and also to the
> > organisation of network code in the kernel.
> 
> I have no idea -- Probably someone like Carl Howe would know that.  I had 
> little to do with the kernel or the machinery.  

The final nail in the coffin of the C-series machines as competitive UNIX
computers was the fact that there was no virtual memory.  I believe the max
RAM a C/70 could have was 2-megabytes.  That was substantially more than the
PDP-11s we had available, but really not competive with the DEC VAX series.

The VAX didn't exist at the time the MBB was first designed, but it was
available by the time the C/70 with BBN-UNIX was first sold.

We probably had about 10-15 developers assigned to a C/70 development
machine and it wasn't too bad until you used certain "memory hungry"
applications.  At the time most BBN developers used the in-house screen
editor called Pen, but I preferred Gosling Emacs.  Launching Gosling emacs
on a multi-user C/70 took literally minutes.  As a result, I'd start it in
the morning and leave it running all day.  I'm not sure BBN-UNIX originally
had job-control, but it soon did.  Plus, you could use the BBN BitGraph
terminal's clever window manager (author Dave Mankins) to have one window
running emacs and others for shells.

Several C-Machine anecdotes:

The typical mass storage in a C/70 was a winchester-type hard disk of some
sort, about 14" in diameter.  I believe the canonical capacity at first was
80-megabytes and you could put two of them in the rack with the computer.
They were in drawers underneath the CPU.  The problem was that if you pulled
out both drawers at the same time, the machine would tip over on top of you.
One of the solutions for this was an ECO that was named something on the
order of "ECO-PB" because it consisted of two lead bricks you would place in
the base of the rack to re-balance it to avoid tipping!

For the most part the C/70 and the C/60 were identical, but the C/60 had a
slower clock.  If you had bought a C/60, you could subsequently buy a "C/70
upgrade" which consisted of a BBN support person coming to your site and
merely either cutting the right wire or replacing the clock chip.  (I can't
remember which.)

Early in my career (and early in the life of BBN-UNIX) I was writing some
shell script and while I was debugging it, the machine crashed.  This was
tedious because it took something like 15-20 minutes to reboot.  Once it was
up, I continued my debugging where I left off and the machine crashed
again.  While it was coming up, I speculated whether my shell script could
be crashing the machine.  Of course, when it was up I had to test this
theory by running the script a third time, causing the machine to crash
again.  I was previously skeptical that a shell script could crash a
machine!  Let me tell you, the other developers on that machine weren't
happy with me that day.

The NU system for monitoring the ARPANET (and the ARPANET itself) eventually
got large enough that the C/70 started running low on memory causing it to
be very slow.  I had been advocating porting the entire NU system to a VAX
running BSD to get more address space.  This fell mostly on deaf ears
because BBN made good money selling C/70 systems for managing our clients'
packet networks.  Eventually someone (Jim Herman? John Sax?) came to me and
asked me to estimate how much effort it would take to port NU to BSD.  He
and I talked about it for half an hour or so and I came up with a number.
(Please remember this was quite early in my career!)  Whoever it was said
"Good.  Thank you.  Eric Rosen told me to come and ask you for your estimate
and then multiply the answer by ten."

--Jim Dempsey--