Thunderbird/5.0   
   .programmer.nt.kernel-mode,comp.sys.ibm.pc.hardware.chips   
   UTC)   
   .os2.apps:1867 comp.os.ms-windows.programmer.nt.kernel-mode:717    
   omp.sys.ibm.pc.hardware.chips:1315   
   From: Jonathan de Boyne Pollard    
      
   > 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.   
      
   --- Internet Rex 2.31   
    * Origin: virginmedia.com (1:261/20.999)