[ih] A small story of IMP #1 and the UCLA Computer Club

Mon Jun 1 14:37:19 PDT 2026

While we are in anecdote mode, the Sigma-7, like other processors, could be
used to toggle a flip-flop at various rates to produce sound. This was
usually accomplished by putting the machine into a loop with a certain
repetition rate. One of the senior graduate students was into computer
music. One day, I brought a friend to see the Sigma-7 and the IMP. When we
arrived, the sr. grad. had a set of tuning forks and was adjusting the loop
lengths to match the sounds of the tuning forks. As we approached, I
cautioned my guest to be quiet. "He's tuning the computer, I said...."

v

On Mon, Jun 1, 2026 at 5:21 PM Andrew G. Malis via Internet-history <
internet-history at elists.isoc.org> wrote:

> Craig,
>
> I did my share of Pluribus coding and debugging. The assembly code was
> really no worse than any other once you got the hang of it, it was actually
> somewhat similar to PDP-11 assembler. It was a multiprocessor machine, and
> if any of the processors crashed, the remaining processors would notice,
> send a fresh code reload to the failed processor, and restart it. As a
> result, it was a pain to try to debug issues in the field, although crashes
> would produce dumps for later analysis. The easiest way to debug the code
> in the lab was to shut down all but one processor. We were able to shut
> down (and keep down) individual processors by using the front panel
> switches to write "FADE" into a particular location. We could later reboot
> the FADEd processor(s) manually.
>
> Regarding physically stopping a Pluribus by bullets or hand grenade, I
> certainly believe a hand grenade would damage all of the processors enough
> to bring them all down. One well-placed bullet in each processor would
> probably do it as well, but you would have to do it carefully, not just
> fire willy-nilly at the collection of processors, you could easily miss at
> least one of the processors that way.
>
> Cheers,
> Andy
>
>
>
> On Mon, Jun 1, 2026 at 3:40 PM Craig Partridge via Internet-history <
> internet-history at elists.isoc.org> wrote:
>
> > By the time I joined BBN, the story was that the person shooting the
> > Pluribus had been forced to write programs for it.  It had a BBN-wide
> > reputation for not being programmer-friendly (which is saying something,
> as
> > BBN periodically generated computing platforms which were painful to
> > program -- such as the C70 with 10-bit bytes).
> >
> > Craig
> >
> > On Mon, Jun 1, 2026 at 12:41 PM Jack Haverty via Internet-history <
> > internet-history at elists.isoc.org> wrote:
> >
> > > Another IMP story...
> > >
> > > The "Pluribus" computer was a BBN creation that included highly
> > > redundant hardware, with multiple everythings.   The idea was that no
> > > matter what failed, the system would keep running while repairs were
> > > made.  Of course a Pluribus could be used as an IMP, which was popular
> > > in some government installations.  One day at BBN, I heard this story.
> > > Wasn't there myself, but I can believe it.
> > >
> > > A Pluribus IMP was being decommissioned at some government site.  They
> > > happened to have a variety of military stuff around.   So someone
> > > decided to see if the Pluribus IMP was as reliable as it was touted to
> > be.
> > >
> > > The IMP was set up, still running.   Someone got a rifle (M-16?) and
> > > started shooting at the IMP.  Really.  Sadly I don't recall the number,
> > > but the IMP survived an amazing number of direct hits at point blank
> > > range, and still kept passing traffic.
> > >
> > > Where did those folks in the Computer Club go after leaving UCLA...?
> > > Any of them in ROTC?
> > >
> > > /Jack
> > >
> > > On 6/1/26 11:22, Karl Auerbach via Internet-history wrote:
> > > > This is a trivial, and quite irreverent, bit of Internet history....
> > > >
> > > > I, like several others, were members of the UCLA computer club during
> > > > the late 1960's.  The club's office was in Boelter Hall - not far
> from
> > > > the room that held IMP #1 (and the Sigma computer - along with its
> > > > "Sigma EXecutive" documentation, aka "SEX Manuals".  My project's
> > > > computer, an IBM 7094 - with a true memory leak [the core memory was
> > > > oil cooled, and that oil leaked] - was in the next room over and we
> > > > could hear the squeals from the AM radio caused by the RF noise from
> > > > the IMP and the Sigma.)
> > > >
> > > > Anyway, folks in the Computer Club - especially Mark Kampe - kinda
> > > > like to pull pranks.  For instance, we would drop things from the top
> > > > of Boelter Hall (9 floors up) to see what would happen.  The landing
> > > > zone was the collection of crunched and bent automobiles resulting
> > > > from the early crash-tests of my group, the Institute of Traffic and
> > > > Traffic Engineering.  We dropped everything from frozen superballs to
> > > > a lead container used to hold/transport radioactive materials [it was
> > > > empty].  There was also a feisty ice-cream vending machine in the
> > > > hallway that once-too-often failed to deliver the paid-for frozen
> > > > treat - so someone in the club unplugged the machine for a few hours,
> > > > everything inside melted, and then plugged it back in, re-frezzing
> the
> > > > leaking drippy mess.  That was not nice, but it was - here's a
> > > > terrible pun - that vending machine received its just desserts.
> > > >
> > > > Anyway, back to Internet History...
> > > >
> > > > IMP #1 had the rough appearance of an armor plated refrigerator, with
> > > > lifting lugs on the top.  The machine was "ruggedized".
> > > >
> > > > That word, ruggedized, was like honey to ants - it seriously caught
> > > > our attention.  So we (I think Mark K. in particular) asked "Is it
> > > > rugged enough to survive a drop from the top of Boelter Hall?".
> > > >
> > > > So our imaginations lit up with images of us grabbing IMP #1, hauling
> > > > it up to the roof and dropping it into the crashed cars nine floors
> > > > below.
> > > >
> > > > Obviously, prudence and sanity - and perhaps even some, probably
> > > > reluctant, respect for law - prevailed.  We never did get beyond the
> > > > "what if we did this" stage.
> > > >
> > > > (But a couple of years later some of us migrated from UCLA to SDC in
> > > > Santa Monica.  At SDC we had an extremely awful HP 2000 minicomputer
> > > > that, if I remember properly, did actually suffer such a fate as it
> > > > was dropped it from the roof of the Q7A building - three stories tall
> > > > - onto the parking lot - a fate that all of us applauded. [It was
> > > > truly a terrible machine with an even worse operating system.]  Some
> > > > of use, years later, moved onto the Interop show nets were we
> sometime
> > > > had to practice the delicate art of percussive maintenance.)
> > > >
> > > >         --karl--
> > > >
> > >
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