Disabling ACPI Support in Windows 2000/XP
Last Updated: 05 Mar 2002
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ACPI is a upgrade to the old power management spec (APM).
In addition to power management, it can alleviate device
IRQ issues (for peripherals with well-written drivers) by
allowing the OS to arbitrate IRQ allocation instead of
the BIOS. This results in lots of IRQ sharing (commonly
on IRQs 9 or 11).
While such a scenario will initially strike panic in the
heart of anyone who has working on PCs in the pre-PnP
era, it works fine for most compliant peripherals.
Thus, IRQ assignments are less important, unless you have
an older peripheral or poor drivers.
If, for some reason, you need to get Win2K to stop using
ACPI, the Microsoft approved method of changing an ACPI
HAL to an APM HAL is to rebuild the machine.
Here are some alternate (less drastic) solutions:
DURING INSTALLATION (APPROVED)
Essentially, you must press [F5] at the beginning of
setup so that you can choose the APM HAL (Standard PC).
AFTER INSTALLATION (NOT MS APPROVED)
For Win2k, you can attempt to change the HAL, bearing
in mind that this process does not update everything
properly when switching between ACPI and Standard
machine types, so there is at least a small chance of
it not working.
NOTE: It is a good idea to copy ALL of the necessary
drivers to your hard drive before proceeding...
I've used this procedure twice, so far, without any
problems. Just be sure to have ALL of your drivers
on hand after the first reboot, because Windows will
ask you for each and every one of them...
Also, don't accept any offers to reboot until the
process is *completely* finished. If you do not
have the drivers in a convenient location (remember
that your floppy or CD may be unavailable for a time)
you can always point the OS to the already installed
*.SYS files in "...\System32\Drivers".
WHITEPAPERS & TECH DOCUMENTS
ADDITIONAL SEARCH OPTIONS (MS KB)
ALL WORDS .............. "ACPI"
EXACT PHRASE ........... "IRQ SHARING"
• So far, I have seen ACPI work a whole lot better in
Intel-based systems than on AMD (Athlon/Duron) based
systems (based on VIA chipsets, to be precise). If
you have a problem with sporadic lockups or reboots,
and you're sure that your machine is being sufficiently
cooled, then you might want to change to "Standard PC"
because one or more of your PCI cards may be unhappy
about sharing IRQs...
• Microsoft recommends that PnP be set to "Disabled" or
"NO" in the BIOS for Windows NT/2000/XP. I haven't
found it to matter one way or the other, but I always
set NT, 2000 and XP to "NO". It's annoying to try and
remember all the weird BIOS settings you might have made
in the past, when things suddenly stop working on your
• Newer devices with good drivers tend to be very well
behaved with IRQ Sharing. HighPoint controllers don't
appear to play well with IRQ sharing, though.
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