> I'm trying to get to the bottom of whether or not any computing equipment > made around the advent of UNIX systems (or any time-slicing system) used > the mains cycles of 60Hz as phase lock for the internal system clock.
The IBM 360 series bumped a register in low memory by 300 counts per second. It used an interrupt from the power line. If you were running on 60 Hz, they added 5 each interrupt. If you were running on 50 Hz, they added 6 each interrupt. I assume that was in the microcode. I wouldn't call it a phase lock. The timer was just driven by the interrupts. I remember a story from the late 70s (I think) of some gear shipped to Europe that wasn't keeping good time. It turned out to be 60 Hz gear that was running off a box to make 60 Hz from 50 Hz. The box wasn't adjusted very well so the clock was drifting. Somebody adjusted the frequency and we went back to working on other things. [I think it was gear that I was familiar with, but all the gear I remember from back then derived time from the CPU clock. Old age...] -- These are my opinions, not necessarily my employer's. I hate spam. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
