1.1 ACPI Component Architecture (ACPICA).The UEFI Forum published the latest version of the standard, "Revision 6.4", in end of January 2021. In October 2013, ACPI Special Interest Group (ACPI SIG), the original developers of the ACPI standard, agreed to transfer all assets to the UEFI Forum, in which all future development will take place. Intel, Microsoft and Toshiba originally developed the standard, while HP, Huawei and Phoenix also participated later. ACPI then executes the desired operations written in ACPI Machine Language (such as the initialization of hardware components) using an embedded minimal virtual machine. Internally, ACPI advertises the available components and their functions to the operating system kernel using instruction lists (" methods") provided through the system firmware ( UEFI or BIOS), which the kernel parses. BIOS, UEFI), the computer hardware components, and the operating systems.
ACPI defines hardware abstraction interfaces between the devices firmware (e.g. The specification is central to the Operating System-directed configuration and Power Management ( OSPM) system. ACPI brings power management under the control of the operating system, as opposed to the previous BIOS-centric system that relied on platform-specific firmware to determine power management and configuration policies. First released in December 1996, ACPI aims to replace Advanced Power Management (APM), the MultiProcessor Specification, and the Plug and Play BIOS (PnP) Specification. Plug and Play and hot swapping), and to perform status monitoring. putting unused hardware components to sleep), to perform auto configuration (e.g. In a computer, the Advanced Configuration and Power Interface ( ACPI) provides an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. When in this mode, the PC can be disconnected from the power source and any maintenance, repairs or upgrades carried out.Example of ACPI tables of a Lenovo laptop. The Global state G3 (Mechanical Off), as its name suggests, is when the system is completely powered-down by using the main power button of the computer's power supply unit (usually a rocker switch on the back). When a machine is in this state the case covers should never be removed as there is still residual power to the motherboard. The Global state G2 (Soft Off) is when the system is powered-down but can be brought back to life by the case's soft power button (usually located at the front of the PC) or other method such as "Wake-on-LAN". Within these Global states are various different Sleep states: S0, S1, S2, S3, S4 and S5.įor example, when you have not moved your mouse or touched a key for a certain period of time the computer's monitor will power-down, this is actually Global state G0 with Sleep state S0.Īnother example is when your computer is put into hybernate mode, this is actually Global state G1 with Sleep state S4. For example, when your computer goes into hibernation mode, the operating system is using the ACPI specification to control the power to the internal components.ĪCPI specifies various modes, referred to as states, that control the power to the components of a PC.
Microsoft stopped supporting the APM specification in their operating systems from Windows Vista onwards.ĪCPI allows the operating system to communicate with the computer's BIOS and instruct the BIOS to power down peripherals. Since Windows 98, ACPI has replaced the older APM (Advanced Power Management) specification (used in Windows 95). It was originally intended for laptops/notebooks where power saving is vital. The ACPI specification allows an operating system to communicate with, and to control the power distribution to peripherals such as hard drives.