We rescued two PDP-11/34 computers and their associated equipment from a storage unit in the Bronx and have been working on getting them running again. The computing system included multiple RK05 hard drives, two RL02 decpack drives, a TU11 tape drive and tons of media, including “digitized monkey brains“. Read on for more details and the exciting boot sequence.
The PDP-11 uses a wire-wrapped Unibus backplane with functions split across many cards. The top four are the CPU/FPU and cache, the next is 64 KB of memory, then a few “bus grant cards”, the console controller, some others, and finally the disk controller.
Adding or removing cards required adjusting the wirewrap on the bottom of the backplane as well as installing bus continuity cards, so the rack slides are built to allow the CPU chassis to be positioned at 45 or 90 degrees for easy access.
The boot sequence had to be toggled in on the earlier models, but the /34 has an octal keypad so you can type the addresses and values rather than flipping binary switches. One of ours has a sticker with the boot sequence printed on it and we’ve singled stepped through it to verify that it works.
However, we’re lucky that this machine has a M9312 “bootstrap / Unibus terminator” board, which has a several small bootroms for different devices like the RK05 decpack drive, RL02 harddrive or TU11 tape drive and also includes a serial console interface. This card allows the the machine to be booted with push button convenience using the VT100 terminals that we’ve restored.
When faced with the bootup of an unfamiliar OS from the 1970s (we’re all Unix kids), “DIR” seems to be the most likely command. For a full walkthrough of the RT-11SJ boot sequence, check out trmm.net/PDP-11 or just ask for HELP.