(Advanced Configuration and Power Interface) A power management specification developed by Intel, Toshiba and Microsoft that makes hardware status information available to the operating system. ACPI enables a PC to turn its peripherals on and off for improved power management, especially in portables. It also allows the PC to be turned on and off by external devices, so that the touch of a mouse or the press of a key will "wake up" the machine.ACPI combines the earlier Advanced Power Management (APM) and PnP BIOS into an enhanced power management system. Starting with Windows 98, ACPI support was built into Windows, and PC chipsets and BIOSes were upgraded to support it. See OnNow.