Christmas in April

Several weeks back, I received a message from one of my favorite teachers. He said that Christmas was coming in April, and that we should get together soon.

Something he had seen on-line practically called my name he said. He ordered one and it had just arrived from Switzerland. It was in kit form and that we would have to put it together and make it work. We made a plan for him to come visit for a long weekend, and we would assemble this electronic computing machine.

I call it a machine because it has mechanical switches, 30 actually – SPST (single-pole, single-throw in electronics jargon). It also has two knobs for rotary encoders, and a power switch. In the old days of computers, we used SPST switches to record ones and zeros – both for specifying an address in memory and loading that address with data. Older computers had tiny incandescent bulbs for indicators, but inexpensive and long-lasting LEDs soon took on that role. And they look way much cooler.

PiDP-11/70 front panel

However, that describes the front panel only – as the rest of the original computer hardware took up multiple cabinets, multiple racks, sometimes a whole room full of equipment. This particular computer’s  ‘engine‘ is actually only a few square inches, and is considerably more powerful than the one it is simulating.

The Raspberry Pi engine

I say simulating, as one of the programs that this new Raspberry Pi hardware can run is a program that can simulate the entire software environment of the world-renown PDP-11/70. This particular setup is known as the PiDP-11.The PDP-11 line of computers was manufactured by Digital Equipment Corporation (DEC) starting in the 1960s, and swept the world as a ‘super-minicomputer’.

This is a nice history of the PDP-11 :

So, let me <POP> the stack back to the mystery teacher at the top of the page. Some of you may know him as Dave Sieg, my (only slightly older) brother. (The older we get, the smaller the difference in age…) However much as our Father taught me about how things work, my brother started me into electronics at the tender age of 2 by introducing me to his robot, and he continues to enlighten me, and I try to reciprocate. I always enjoy sharing with him things I have learned.

“Meet my robot, don’t be scared.”

We spent a lot of time together in college at Ole Miss in the 70s, and collaborated on many projects. He was more focused on video (television) and I was more focused on computers (mostly hardware, but some software). After we left Mississippi we were both involved in ham radio, and sometimes we could chat between California and North Carolina or Denver (for free). So for 10 years he did research & development into computer graphics for movies and advertising (in Hollywood CA), while I traveled the country maintaining big computer systems for DEC – based first in NC, but then transferring to Denver CO.

In 1990 we gave up the big city life and returned to our hometown Kingsport TN. David had established ZFx, Inc and invited me to work with him (and help maintain the computers). We started Tricon.Net in 1994, one of the first regional internet providers. As a crucial step forward in my education, he started me on a path to learn about using and maintaining UNIX computers. That single concept kept me employed until my retirement in 2016, after working for a few defense contractors, and finally 10 years supporting the ISS with NASA.

My brother has known me longer than anyone still living, and I am thankful that we can still collaborate and enjoy each others company. David & I still teach each other tips & tricks about this versatile computer environment. Kindof like last month when we got together to build this kit, and actually made it work. I love you more than I can express; Thank You David.<RET>

Soldering diodes and LEDs
All switches soldered, ready to test

Returning to the story at hand, we put this thing together one weekend, and had a great time. It works.!. I love it. I can’t count the hundreds of PDP-11/70s I’ve ever worked on during the decade of my life I devoted to DEC. Currently my PiDP-11 is running the default idled program, and makes a neat desktop appliance with many blinky-lights. However, I can set a number in the switch register, and press the address rotary encoder and the simulation can change to any of the PDP-11 operating systems (DOS-11, RT-11, RSTS-7, RSX11mplus, or any of several early UNIX systems). It can even support serial ports for your VT-100s.!.

Choose your favorite PDP-11/70 operating environment

One can even enter Octal program code from the switch register, if you remember any of your assembly language programming.

A short video from Dave to show the ‘idled‘ program in operation.
(this link is to my SomeNet.NET webserver, I can’t upload video here with a free account)

Here is the detail on the PiDP-11:

If this appeals to you at all, make an inquiry.
The web site claims over 3000 kits sold, so get in line – might need wait a bit.
If the PDP-11/70 meant anything to you, this kit might be what you’ve been missing.


One response to “Christmas in April

  1. Enjoyed your article. Some over my head but lots familiar. I,too, have had a great relationship with my brother who is two years older. My husband ( he was a classmate of my brother at Dobyns-Bennett) and I have traveled the world together and all had a great time. It is so special to have such a great relationship. Thanks for your story. You may be a computer scientist but unlike many, you are are a great storyteller!

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