Hacker News Reader

Comment by crispyambulance | Hacker News Reader

I've always wondered, what _are_ those large groovy switches on the front?

They're just numbered with integers [0..21, colored in groups of 3 presumably for octal]! are they seriously for bit flipping??

View on HN

Yes: http://www.psych.usyd.edu.au/pdp-11/bootstraps.html

That's a "Front Panel" and all computers prior to around 1980 had one. It's the equivalent of the BIOS -- the one thing that's up and running when the power switch is flipped on. If the machine had core memory (which was non-volatile) the FP was seldom needed since the primary boot loader would be left in core long-term (after being toggled in once).

Here's a demo of someone using these switches to enter and run programs on a PiDP-8.

https://www.youtube.com/watch?v=oMRDAD1JNWo

21 bits ... allows front panel access to more than the 16 bits of the machine registers. smokin'!

The /70 had a 22-bit address bus, so I assume that switches 16-21 didn't have any effect unless you were entering a memory address.

I read something that said Ken Olsen found these switches on an old model washing machine and thought they would be great on the PDP machines.

I think it might have been the 1957 Philco-Bendix Duomatic washer/dryer front switches that inspired the PDP-11 panel.

nope you loaded code in as OCD octal coded decimal to boot the system if the bootstrap processor failed or was not present

Yes. They are bit numbers.

Reply on news.ycombinator.com