Your best bet to complete understanding is to look at TimerStart and
TimerInterrupt. But yes, all timers in GEOS are based off the 8253 TIMER0.
TIMER0 is normally set to expire in 1 tick (1/60th of a second) and normal
timers are checked every tick for expiration. Setting a MS timer causes the
8253 TIMER0 to be reprogrammed with the appropriate value (obviously, usually
less than 1/60th of a second). Anyway, once the MS timer expires, the TIMER
is reprogrammed with the standard timer value (1/60 sec).
Nathan