I’m in the process of restoring a recently acquired a DEC PDP-11/23 to operation. This is a rack mountable minicomputer from 1979. It’s a simple machine, but it’s been difficult to get working. Old computers like this can be flakey and hard to diagnose. I’m going to document my progress so future PDP-11 restorers might have a head start!

When purchased, this machine included the following boards:

  • KDF11-AA (M8186) CPU board without a floating point processor
  • MSV-11 (M8044) 32K memory board
  • DLV11-G (M8043) 4 port serial board
  • BDV11 (M8012) bootstrap/terminator board

It also included a network interface from Advanced Computer Communications. I found very little documentation about this interface, but it was used to connect to ARPAnet.

In actual use, this machine would have been connected to tape drives, magnetic storage, and other peripherals. Without any of that, all I can do is connect a serial console and see what happens. Starting the computer with the halt switch enabled causes it to drop right into a debugging console called ODT.

From ODT I was able to enter a simple hello world program, and it worked!

That means my machine is somewhat operational, so the next step is to try booting it from some sort of media. Since I don’t have anything real, I’ll try a TU-58 tape emulator that will run via serial from a Linux machine.