APM (Advanced Power Management) is a PowerManagement standard, developed by Intel and Microsoft, which allows the operating system to control the amount of power sent to devices. ACPI replaces APM as the main power management system for operating systems, mainly because SMP and APM do not mix well.
APM is mainly used by calling 32bit functions through to the BIOS, however, some BIOSes are buggy, a disadvantage of such a method, and is one of the main reasons why ACPI has succeded. However, APM is much simpler to implement in an operating system.
APM information is given in the DMI table.
Official document by Intel and Microsoft describing the APM standard.
I don't know whether the above document is 100% legal, so if someone can enlighten me.. it'd be appreciated -- DennisCgc