ACPI multiprocessor HAL - hot CPU idle

Hi All,

I have recently upgraded the CPU (SL6PG) on a machine running Win2K server.
The CPU has hyperthreading technology. I switched to the ACPI MP HAL and
enabled hyperthreading in the bios. There seem to be no issues and the
system is stable running at 3519 MHz on the stock voltage of 1.55v. However,
I noticed that the idle temps were a bit high so I switched back to the ACPI
uniprocessor HAL. The temps are around 5 or 6 degrees Celsius lower when the
ACPI multiprocessor HAL is used. As I'm not sure what HAL the system was
initially installed with, I can not say it was an ACPI HAL of any sort,
however the motherboard and bios both support ACPI.

So what's going on here? I read that Win2K supports HALTing of the CPU in
the idle loop but not as aggressively as Win2K+3 or XP. It would seem to me
that this is happening with the uniprocessor HAL but not the multiprocessor
HAL. Of course, I wouldn't have a clue! Any suggestions?

Thanks in advance,

Stephan Carydakis