A twist on blinkenlights

While visiting the San Francisco area for the Computer Museum History Center's awards dinner, I swung by Stanford to see their exhibit of old (largely Stanford custom) computer hardware. Various groups at Stanford had computer systems (mostly PDP-6 and -10 I believe), but the exhibit highlights the Stanford Artificial Intelligence Lab, a.k.a. SAIL. SAIL had a multiprocessor system containing a KA10, a KL10, and a PDP-6, as well as two smaller computers dedicated to video control, two megawords of memory (eight times the address space of the -10), and disk storage, so they obviously had enough blinkenlights for anyone. But one of the programmers added a box (looking more or less like a tiny traffic light) to his office. Green meant "normal operation". Yellow meant "parity error". (Failures tended to happen in clumps, so after finding one error, the software would kill the affected job and then search for all other errors and kill all other affected jobs.) Red meant "The OS has halted an Exec-mode DDT is running". (Think "kernel debugger".) No lights meant "Things are really messed up". Not exactly high bandwidth, but still an elegant metaphor! -- Derek