ACPI (Advanced Configuration & Power Interface)

ACPI (Advanced Configuration and Power Interface) is an industry specification for the efficient handling of power consumption in desktop and mobile computers. ACPI specifies how a computer's basic input/output system, operating system, and peripheral devices communicate with each other about power usage. ACPI is a key component of Intel's "Instantly Available" technology. Microsoft refers to its support as "Always On."

With ACPI, the following capabilities are possible (assuming the operating system supports them):

The user can specify at what time a device, such as a display monitor, is to turn off or on.

The user of a notebook computer can specify a lower-level of power consumption when the battery starts running low so that essential applications can still be used while other, less important applications are allowed to become inactive.

The operating system can lower the clock speed during times when applications don't require the full processor clock speed.

The operating system can reduce motherboard and peripheral device power needs by not activating devices until they are needed.

The computer can enter a stand-by mode when no one is using it, but with modem power left on to receive incoming faxes.

Devices can be Plug and Play. As soon as plugged in, they can be controlled by ACPI.

ACPI must be supported by the computer motherboard, basic input/output system (BIOS), and the operating system. One of several power schemes can be chosen. Within a power scheme, the user can control the power to individual devices. In order for ACPI to work on your computer, your BIOS must include the ACPI software and the operating system must be ACPI-compatible. ACPI is designed to work with Windows 98 and with Windows 2000.

ACPI is in part a response to global concerns about energy conservation and environmental control. ACPI replaces Intel's SL technology and the more recent APM (Advanced Power Management) technology. Based on the collaborative effort of Hewlett-Packard, Intel, Microsoft, Phoenix, and Toshiba, ACPI moves away from power management that simply times out during inactivity to a more sophisticated demand-based power management. ACPI components collect information about power consumption from the computer and gives that information to the operating system. The operating system then distributes power to the different computer components on an as-needed basis. With ACPI, the computer can power itself down to a deep sleep state but still be capable of responding to an incoming phone call or a timed backup procedure. Another feature of ACPI is the "hibernation" mode. Before the computer goes into a deep sleep or hibernation, the contents of RAM are written to an image file and saved on the hard drive. When the computer is turned back on, the image file is reloaded, eliminating the need to reboot the system and open applications.