tbray@mprvaxa.UUCP (Tim Bray) (06/25/84)
On the third and fourth CPU boards from the left, on 780s. They flash revealingly when I/O to/from the floppy is going on. If you had ever installed buggy updates to a certain DEC OS that runs on VAXes, you'd know about this.
dmmartindale@watcgl.UUCP (Dave Martindale) (07/03/84)
Actually, the lights on the 4th CPU board in tell you nothing, because they are all partly lighted all the time when the CPU is running. The ones on the 3rd board are the CPU microcode address - they can tell you whether the CPU is idle or not, but not too much else. I believe the uppermost light on that board tells you that the CPU is stopped waiting for something like a memory fetch. Even more useful are the microcode address lights on the Unibus adapter - they show whether there is any unibus activity, and how intense it is.