Your PC also has a quartz oscillator and battery backing, there's no way it synchronizes time from AC power.

sure, I just meant my PC has a very sophisticated (hence fragile) way of keeping its time accurate.

And forget about battery backing, it's a desktop and its bios battery is long dead :-) (hence the atomic clock)

Once you do synchronize it off the net, it's still the quartz oscillator keeping the local beat, as it were :)

I synchronize with ntp every 500 million cpu cycles :p

IIRC modern operatings systems use counters in the CPU for timekeeping instead of directly accessing the RTC

Well, the CPU is somewhat beyond my ken. You are right, of course - yet I think there would be another oscillator driving the clock generator as well. Turtles all the way down ;)