timers

BTW, I think ACPI offers an additional timer that could be used
for this purpose.At least Windows seems to go this route in it's
implemenation of the DosTmrXXX equivalents.

It's not ACPI. It's the hardware. There are three major "timer"
interrupt sources in a modern PC machine: channel #0 of the Programmable
Interval Timer which is nowadays integral to the PCI-to-ISA or
PCI-to-LPC bridge chip, the High Precision Event Timer on the
host-to-PCI bridge chip, and the timers built in to each local APIC.
There are additional sources of *counters*, such as the so-called "PM
timer" and the TSC processor register, which don't generate timer
interrupts.

Which is used when is not simple. It's not possible to say "Windows
uses X", because that varies from HAL to HAL and according to how
Windows happens to have been bootstrapped on each particular occasion.
KeQueryPerformanceCounter() calls HAL functions, and the
USEPMTIMER/USEPLATFORMCLOCK and (old) USE8254 options, passed to the
Windows boot loader and settable on boot manager entries, control how
several of those HAL functions (varying by HAL, of course) behave.