If you look closely into the top of a Cray-2 we are able to make out rows of indicator lights that were used by service engineers to assess the state of a machine. In the event that a machine hung or unexpectedly halted, the indicator lights were examined to gain some idea of what was going on in the machine at the time. We can see below descriptions of the different status lights and and then it in an engineers working notes from one particular incident.
Thanks to Ken Taylor for this valuable insight and Muse Bolo for the machine images.
Cray-2 Module map diagram showing a 4 cpu system and memory board arrangements.
