Software

The process of bringing a computer system from the early minicomputer era back to functioning status is a process of loading programs of ever-greater complexity into the machine, beginning with the ‘bootstrap loader,’ a very short program that allows other programs to be into memory. Since at this stage there are no peripherals, this is done by flicking (‘toggling’) front panel switches on and off to form binary instructions that are then sent to the machine.

Since most PDP-1 software was released on paper tape, it made sense to restore the paper tape reader first. Copies of original paper tapes—some 45 years old—were made so as to not risk damaging them.

Official DEC diagnostic programs were then used to further check out the machine. They included an instruction test program, memory testers and (eventually) programs to exercise the typewriter and paper-tape peripherals.

The key milestone of the machine was to run Spacewar! To do this, every peripheral of the system—as well as the CPU—had to work perfectly. This was accomplished, after much work on peripherals (see “I/O” section) on February 29, 2005.