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ACPI is a standard for computer power management that brings many aspects of device configuration under the control of the operating system. It evolved throughout the 2000s, allowing support for new devices and technologies while maintaining most configuration and management functions in the OS. ACPI is a fundamental part of green computing, allowing the OS to put processors and motherboard components into different levels of “sleep” as needed.
Advanced Configuration and Power Interface is a standard for computer power management. Also known by the acronym ACPI, it brings many aspects of device configuration under the control of the operating system (OS). Most of the legacy power management is implemented in the operating system with ACPI rather than in the basic input output system (BIOS). ACPI is used in computer systems to manage device discovery, power configuration, and thermal monitoring. End users often use ACPI to specify how long devices such as hard drives should be idle before reducing power consumption.
In 1996, the first version of the Advanced Configuration and Power Interface standard was released by a group of computer manufacturers. His goal was to consolidate system power management in one place for servers, laptops and desktops. Before ACPI, many of these functions were performed by the motherboard specific BIOS. Another specification called Advanced Power Management (APM) provided part of the application interface along with the BIOS. Multiprocessor Specification (MPS) tables also played a vital role and were also integrated into ACPI.
The specification for advanced configuration and power interface evolved throughout the 2000s. Support for new devices and technologies was included while maintaining most configuration and management functions in the operating system. The system BIOS and firmware communicate with ACPI through hardware description tables and ACPI Machine Language (AML). These allow platform-independent management code in ACPI to access platform-specific devices on each machine. The ACPI standard also defines fixed-function hardware interfaces to reduce the amount of code required for startup and error recovery.
The requirement for an AML interpreter to be implemented in each operating system has helped slow the adoption of the ACPI standard. The Advanced Configuration and Power Interface Component Architecture (ACPICA) was created in 1998 to assist operating system developers. It includes an OS-independent AML interpreter along with some of the required ACPI infrastructure. ACPICA is designed to allow any operating system to use ACPI rather than being a specific implementation of the operating system itself. It is an open source standard that has evolved over time alongside the ACPI specification.
Power management based on Advanced Configuration and Power Interface is a fundamental part of green computing. Standards like ACPI allow the operating system to put processors and motherboard components into different levels of “sleep” as needed. For example, a Wake-on-LAN network interface can minimize power consumption until no traffic is detected. An entire system can be shut down except for its main memory, waiting for a particular key press to restore operation. Some green motherboards even have an entire processor dedicated to managing system power.
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