DOS ACPI power off utility

Solaris x86 10 is free. You can enable the ACPI poweroff debug mode, and then power off the PC via the OS (which will do it via ACPI) and see what the debugging messages tell you. You could do this all from the install CD without actually installing Solaris on the PC.

In my experience, lots of PC's have faulty BIOS's when it comes to powering off using ACPI. A common fault is the BIOS installed by the board manufacturer does not match the chipset on the motherboard, i.e. the S5 method returns the wrong two values to write to the registers to power off the machine. I suspect this happens when the manufacturer builds BIOS's for multiple motherboards and forgets all the things they need to change in the BIOS. I've seen a number of Dells with this problem. If the OS contains a feature for the user to override the ACPI BIOS, you can work around this one, but the fault is in the BIOS, which from the users point of view probably counts as hardware. I also found some HP workstations such as xw6000 which couldn't ACPI poweroff. This looked like a hardware problem as trying all 8 possible S5 values failed to work, although some would lock up the machine in strange ways. The manufacturer had set the S5 ACPI method return two zeros, which might have been a crude way to disable ACPI poweroff if they knew it didn't actually work.

So in my experience, failure-to-power-off-after-shutdown via ACPI is normally a BIOS or hardware problem. If you are a field engineer tracking this down, I would start by making sure the motherboard has the latest BIOS, even though I don't actually recall any case where I found a manufacturer had fixed this fault in a BIOS update.

In terms of Software, I think there are very few different ACPI implementations in the various OS's. I know of only 3 -- Intel's open source one, Microsoft's (although this might be Intel's too, I don't know), and Sun's Solaris x86 one (which was a very early implementation, and will be replaced with Intel's in the future).

Note that ACPI is not the only method to power-off-after-shutdown. The earlier APM method is probably still in most current BIOS's even though APM is now obsolete. Another option is for an OS to have a motherboard chipset driver which recognises the chipset the mother- board uses and directly accesses the relevant registers, although this is probably rare nowadays (there are just too many motherboard chipsets to keep up with them all this way).

-- Andrew Gabriel