#minicomputer

🎄💾🗓️ Day 4: Retrocomputing Advent Calendar - The DEC PDP-11! 🎄💾🗓️

Released by Digital Equipment Corporation in 1970, the PDP-11 was a 16-bit minicomputer known for its orthogonal instruction set, allowing flexible and efficient programming. It introduced a Unibus architecture, which streamlined data communication and helped revolutionize computer design, making hardware design more modular and scalable. The PDP-11 was important in developing operating systems, including the early versions of UNIX. The PDP-11 was the hardware foundation for developing the C programming language and early UNIX systems. It supported multiple operating systems like RT-11, RSX-11, and UNIX, which directly shaped modern OS design principles. With over 600,000 units sold, the PDP-11 is celebrated as one of its era's most versatile and influential "minicomputers".

Check out the wikipedia page for some great history, photos (pictured here), and more -

And here's a story from Adafruit team member, Bill!

The DEC PDP-11 was the one of the first computers I ever programmed. That program was 'written' with a soldering iron.

I was an art student at the time, but spending most of my time in the engineering labs. There was a PDP-11-34 in the automation lab connected to an X-ray spectroscopy machine. Starting up the machine required toggling in a bootstrap loader via the front panel. This was a tedious process. So we ordered a diode-array boot ROM which had enough space to program 32 sixteen bit instructions.

Each instruction in the boot sequence needed to be broken down into binary (very straightforward with the PDP-11 instruction set). For each binary '1', a diode needed to be soldered into the array. The space was left empty for each '0'. 32 sixteen bit instructions was more than sufficient to load a secondary bootstrap from the floppy disk to launch the RT-11 operating system. So now it was possible to boot the system with just the push of a button.

I worked with a number DEC PDP-11/LSI-11 systems over the years. I still keep an LSI-11-23 system around for sentimental reasons.

Usagi Electric, Forgotten Machines, & Nevets at VCF Southwest 2025

[Usagi Electric], [Forgotten Machines], and [Nevets01] collaborated on a massive exhibit of unique old hardware.

[Usagi Electric] had an interactive exhibit with his recently rebuilt PDP 11/73 running examples of spectroscopy analysis using a Bomem vector processor. [Usagi] also demonstrated a Data General Nova 1210 running BASIC.

[Forgotten Machines] had a variety of old terminals, computers, and peripherals on display. He was on-hand throughout the show to help anyone image and preserve their old magnetic media.

[Nevets] had an interactive exhibit with a Data General Nova 1200 running BASIC alongside a (sadly non-functional) Digital Computer Controls D-116, a clone of the Nova 1200.

It's gonna take a loooot of work to get it functional, especially the DS10 disk drive (which is just a CDC Hawk with a TI badge slapped on), but hopefully I can bring it back to life :3 Looking forward to programming it, since the 990 series has pretty cool features, like easy context switching.

PolyMorphic Systems Poly-88

Minicomputer