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

[Andrew G. Malis]

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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