Windows XP offers enhanced power-management features for desktop and mobile computers. Windows XP follows Windows 2000 in supporting the Advanced Configuration and Power Interface (ACPI) specification, which provides reliable power management and system configuration. Windows XP also provides more limited power management support for systems based on the legacy Advanced Power Management (APM) API.
On an ACPI-compliant system, the operating system manages, directs, and coordinates power so the system is instantly accessible to users when needed, while remaining silent and consuming the least possible power when not actively working. In earlier power management architectures such as APM, the BIOS controlled the power state of system devices without the involvement of the operating system.
Devices and applications designed in compliance with the ACPI specification can respond to or request a change in the system power state. For example, an active application or input from a device, such as a mouse, indicates to the operating system that the computer or device is in use. The operating system's power policy manager then allocates full power to the system. Otherwise, the operating system tries to put the computer into a lower power or sleep state. For example, a fax modem can operate while the system is in standby, consuming little energy until the telephone rings, at which time the system can wake up to receive a fax, and return to standby when the system is no longer needed.
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