What Is The Full Form Of ACPI?
The full form of ACPI is Advanced Configuration and Power Interface.
ACPI, in a computer, provides an open standard that the OS (operating system) can use for managing power. It assists an OS in controlling the amount of power that goes into other computer devices when not in use, like printers, CD players, etc. An operating system can utilize ACPI for discovering and considering the components of computer hardware, putting unused ones to sleep for power management, performing status monitoring, and auto-configuration (like hot swapping Plug and Play).
Introduced by Intel, Microsoft, and Toshiba, the ACPI brings management of power under the control of the OS. It is opposite to the BIOS-centric system previously that determined power configuration and management policies by relying on platform-specific firmware.
History
- The very first revision of the ACPI specification supported 32, 24, and 16-bit addressing spaces, released in December 1996.
- ACPI finally received 64-bit address support in August 2000. It also received multiprocessor workstations and server support with revision 2.0.
- Revision 3.0 – Released in September 2004. It brought the ACPI specification support for PCI Express bus, SATA interfaces, ambient light sensors, multiprocessor support for about 256 processors, user-presence devices.
- Revision 3.0 also extended the thermal model beyond the processor-centric support used previously.
- Revision 4.0 – Released in June 2009. This specification added a variety of new features to the ACPI design. The most notable ones are the logical processor idling, x2APIC, and USB 3.0 support.
- Revision 5.0 – Released in December 2011. It added support for the ARM architecture.
- Revision 5.1 – Later released in July 2014.
- Revision 6.3 – Released in January 2019. It is the latest specification revision.
Characteristics of ACPI
- ACPI helps in the power management of the system.
- It directs the computer regarding the programs that need power at any instance.
- It also gives a few controls to the user- like setting up the sleep time.
- ACPI shifts the contents to an image file, then saves them in a computer’s hard drive. This way, the system restores the content easily once the computer switches on.
Performance State
When a processor or device operates (C0 and D0, respectively), it can stay in one of the various power-performance states that are implementation-dependent. Here’s a list of some power states:
- P0 – Maximum frequency and power.
- P1 -It is less than P0. Frequency and voltage scaled.
- P2 – It is less than P1. Frequency and voltage scaled.
- Pn – It is less than P(n–1). Frequency and voltage scaled.
Benefits of ACPI
- It saves power, and thus, saves battery. Computers can utilize their batteries for longer with ACPI.
- It provides hibernation mode as well.
- A user is free to set the shut-down time for their device.
- ACPI allows an OS to reduce the power it gives to the motherboard.
- It can also alter and reduce the power given to various other devices that might not be in use.
Limitations of ACPI
- ACPI may lead to a problem when it puts the _ADR devices in a deep sleep.
- It also creates an issue when a bus is expecting (for attaching hardware devices like PCI) while the devices stay in a deep sleep. It happens because buses don’t expect the devices to get disconnected when they are in power-down mode.
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