The PDP 8/a was the last model of the PDP-8 series.

Date of Production: 1976

CPU: 12 bit

Random access memory installed: 8 kW core memory

Max. random access memory: 32 kW core or MOS memory

I/O busses: OMNIBUS

Serial number:




This PDP 8/a only found the way to me due to the lucky hint of one of my good friends in 2004, who had seen a metal box with electronic disposals in a floor of our institute. We checked the content by using the good old method of "dumpster diving" and amazingly, I found this black chassis and only saw the hex-wide board. I jumped around in circles, as Í thought, that this would be some sort of Unibus-based system (?).

During that time, I didn't now anything about Omnibus-based systems and that this might by a PDP-8! Another friend of mine told me, that I needed to get out all the remaining parts of the PDP, which still might be in the metal box. The second look was successful; I discovered the basic front panel and the electronics of the programmable front panel (with the calculator-like buttons). Apparently, somebody took the fancy white front panel home for memorials and maybe nailed it on his wall. But anyway, I prefer having the electronics rather than the white panel. Apart from that, the fans were missing.

This system used to do processing work for a measuring instrument at the institute for high frequency applications. Therefore, no periperals are provided, only the mini-computer itself.

It took some time to check, if nothing was missing or visibly faulty. The power supply caused some confusion, as there was a circuit path, which had melted! Finally, after a small fruitful discussion with one of the electronics guys at the institute, it became clear, that this wouldn't have an influence on the correct functioning, as this was part of a security circuit.

The first power-up followed serveral months later after the intense checking of the system.

Thankfully, the PDP came up without any problems. I could successfully store bits into the core memory and read them out by using the front panel as you can see on the pictures. As said before, the white plastic panel, holding the electronics, is missing.

More Pictures of the PDP 8/a:

PDP-8 CPU This is the CPU-board of the PDP-8/a.