Digital Equipment Corporation - PDP-5

The PDP-5 was DEC's predecessor to the very successful PDP-8. This one came from Bob Woodhead who rescued it from the trash dump where it had been thrown out by the Navy. He had some electronics technicians working for him that he needed to train and the PDP-5 provided just the right amount of interest and complexity. Once restored to working order he kept it (resisting all prompts from others to "throw out that piece of junk.") until he mentioned it to me when I met him. At that time I offered to take over its care should he ever need the space in his garage back. Sometime later he contacted me and offered it to me. After a lot of planning and a couple of botched attempts, I managed to get it from its former home back to Silicon Valley where it sits to today undergoing restoration and testing. Prior to April 2000, it was estimated that the last time it had been powered up was 1985. Fifteen years is a long time for electronics to sit, and I am being very careful with this priceless example of computer history!

Image Gallery

In the future I'll have more information here about the PDP-5, its operation, and its schematics, however for now I've got mostly pictures. Follow the links to see this wonderful machine "up close" as it were:

• Waiting for Rescue -- This is the PDP-5 outside Bob's garage.
• Front Panel -- The basic front panel, minimalist compared to things like the PDP-11/70 but completely functional for its time.
• Back Panel -- Unlike modern computers, the PDP-5 used -3v logic! It is all transistor based and you use the large knob to set the voltage of the bus to the "center" of the computer's operating range.
• Open Front -- With the doors open you can see the back plane at the top and the I/O plane at the bottom of the cabinet.
• Flip Chips -- Before there were IC's to make computers with DEC invented the "Flip Chip." A small dedicated circuit card that had from one to six logic gates on board. These are wired together on the back plane to create the computer.
• Core Memory -- Embedded in the back plane is a 4K word core memory stack. This was actually built by a third party for DEC as DEC had not yet started making their own memory.
• Power Supplies -- The power for the machine comes from four power supplies (two for logic, one for memory, and one for I/O). These are built onto panels that are attached to the back of the rack.