Advanced Configuration and Power Interface
The key element of the standard is power management with two important improvements. First, it puts the OS in control of power management. In the currently existing APM model most of the power management tasks are run by the BIOS, with limited intervention from the OS. In ACPI, the BIOS is responsible for the dirty details of communicating with hardware equipment but the control is in the OS.
The other important feature is bringing power management features now available only in portable computers to desktop computers and servers. Extremely low consumption states, i.e., in which only memory, or not even memory is powered, but from which ordinary interrupts (real time clock, keyboard, modem, etc.) can quickly wake the system, are today available in portables only. The standard should make these available for a wider range of systems.
For ACPI to work the operating system, the motherboard chipset, and for some functions even the CPU has to be designed for it. Microsoft is heavily driving a move toward ACPI, both Windows NT 5.0 and Windows 98 will support it. It remains to be seen how much hardware manufacturers will embrace the technology and whether other operating system vendors will support it.