[PLUG-TALK] Nerdgasm - using a Raspberry PI to recreate a PDP8

Keith Lofstrom keithl at gate.kl-ic.com
Sun Mar 29 11:35:31 PDT 2015

On Fri, 27 Mar 2015, Michael Rasmussen wrote:
On Sat, Mar 28, 2015 at 05:47:18AM -0700, Rich Shepard wrote:
>   How kewel that is! Brings back memories of the remote job entry terminal
> to the IBM S/360 in my lab building at the U. of Illinois in the early
> 1970s. The PDP-8 controlled the card reader and line printer as well as
> communications to the mainframe.

The first computer I ever worked on was a PDP-8/S (S == small,
slow) at Tektronix in 1969.  I was a high-school member of
Explorer Scouts 876, which met at Tektronix Beaverton on
Thursday evening (and had a reunion two weeks ago). 

That PDP-8/S was used by mechanical engineers during the day
to prepare paper tapes for production machine control; no disk
or mag tape.  It had an ASR33 teletype (with the tape reader+
punch on it) for input, "permanent" storage, and printout.

On Thursday nights, we would use the front panel switches
to toggle in the simple paper tape boot loader (16 words,
IIRC).  That loaded a more capable boot loader off a short
paper tape, which in turn loaded the long FOCAL "language"
paper tape.  Reusing the same tiny magnetic core memory (4K?)
each time, snake eating its tail.  Get the sequence wrong,
start over with toggle switches.  Did I mention "slow?".

We would write our 20 line programs on grid paper, then type
them into the teletype to make paper tape.  The only error
correction was backspacing, then punching "delete" (all holes
punched) over incorrect characters and adding more characters to
the paper tape after the deletes.  When the program tape was
ready, we would feed it into the teletype, the PDP-8 would
"think" (slowly), and print out the results on the teletype.

My first program was a dozen lines of algebra; it took two
trigger voltages as input, and calculated three resistor values
for a two transistor "Schmitt trigger" circuit intended to
have those high and low trigger voltages.  Computer aided
design, later the core tool of my engineering career.

My friends whose parents had money bought them OMSI memberships.
They played in Rusty Whitney's PDP-8 lab in the basement at the
old OMSI.  I got to visit once; stay-back no-touch, unrequitted
lust, the beginning of an unconscious obsession. 

A dozen years later, after college, and with a decent engineering
job, that ancient, way-obsolete three-racks-of-gear OMSI PDP-8
was put up for auction.  The lust returned with a vengence.  I
can HAVE IT.  I have NO USE for IT.  IT would BREAK my APARTMENT
FLOOR.  IT would SET FIRE to the FUSE BOX.  I WANT IT!!!!

I stayed home with the phone disconnected, hiding from the world
and my uncontrollable lust for a week, until some other obsessive
bought it. 

Be very careful what you wish for as a teenager, when your brain
is still furrowing the deep grooves of personality, or you will
end up with something as inconvenient as a ton-weight computer
less powerful than an a programmable pocket calculator.  

It isn't the type that matters, it isn't the function, it is the
specific object of our desires.  Duels have been fought over less.


Keith Lofstrom          keithl at keithl.com

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