# ACPI > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/ACPI > Markdown URL: https://mediated.wiki/source/ACPI.md > Source: https://en.wikipedia.org/wiki/ACPI > Source revision: 1354564089 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Computer firmware interface standard}} {{Use mdy dates|date=January 2015}} {{For|others|ACPI (disambiguation)}} {{Infobox technology standard | title = Advanced Configuration and Power Interface | long_name = | image = | image_size = | alt = | caption = | abbreviation = ACPI | native_name = | native_name_lang = | status = Published | year_started = | first_published = December 1996 | version = 6.6 | version_date = May 2025 | preview = | preview_date = | organization = {{Plain list| * ACPI [SIG](/source/Special_interest_group) (1996–2013) * [UEFI Forum](/source/UEFI_Forum) (2013–present) }} | committee = | series = | editors = | authors = | base_standards = | related_standards = [UEFI](/source/UEFI) | predecessor = {{Plain list| * [Advanced Power Management](/source/Advanced_Power_Management) * [MultiProcessor Specification](/source/MultiProcessor_Specification) * [Plug and Play BIOS](/source/Plug_and_Play_BIOS) }} | domain = [Power management](/source/Power_management) firmware | license = | copyright = | website = {{URL|https://uefi.org/acpi}} }} '''Advanced Configuration and Power Interface''' ('''ACPI''') is an [open standard](/source/open_standard) that [operating system](/source/operating_system)s can use to discover and configure [computer hardware](/source/computer_hardware) components, to perform [power management](/source/power_management) (e.g. putting unused hardware components to sleep), [auto configuration](/source/Auto-configuration) (e.g. [plug and play](/source/plug_and_play) and [hot swapping](/source/hot_swapping)), and status monitoring. Launched in December 1996 and first available in [Windows 98](/source/Windows_98) and [Windows 2000](/source/Windows_2000), ACPI aims to replace [Advanced Power Management](/source/Advanced_Power_Management) (APM), the [MultiProcessor Specification](/source/MultiProcessor_Specification), and the [Plug and Play BIOS](/source/Plug_and_Play_BIOS) (PnP) Specification.{{cite web |url=http://www.acpi.info/presentations/ACPI_Overview.pdf |website=www.acpi.info |title=ACPI Overview |format=[slide show](/source/slide_show) in PDF |archive-url=https://web.archive.org/web/20190525060308/http://www.acpi.info/presentations/ACPI_Overview.pdf |archive-date=2019-05-25}} 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.{{cite web| url = http://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/APMV12.rtf| title = APM BIOS Specification| publisher = [Intel Corporation](/source/Intel_Corporation), [Microsoft Corporation](/source/Microsoft_Corporation)| date = February 1996| access-date = 2010-07-02| format = RTF| archive-url = https://web.archive.org/web/20120206030045/http://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/APMV12.rtf| archive-date = February 6, 2012| url-status = dead}} The specification is central to the '''Operating System-directed configuration and Power Management''' ('''OSPM''') system. ACPI defines [hardware abstraction](/source/hardware_abstraction) interfaces between the device's firmware (e.g. [BIOS](/source/BIOS), [UEFI](/source/UEFI)), the [computer hardware](/source/computer_hardware) components, and the [operating system](/source/operating_system)s.{{Cite web|title=What is ACPI (Advanced Configuration and Power Interface)? - Definition from WhatIs.com|url=https://searchwindowsserver.techtarget.com/definition/ACPI-Advanced-Configuration-and-Power-Interface|access-date=2020-09-18|website=SearchWindowsServer|language=en}}{{Cite web|title=ACPI Device Tree - Representation of ACPI Namespace — The Linux Kernel documentation|url=https://www.kernel.org/doc/html/latest/firmware-guide/acpi/namespace.html|access-date=2020-09-18|website=www.kernel.org}} Internally, ACPI advertises the available components and their functions to the [operating system kernel](/source/operating_system_kernel) using instruction lists ("[methods](/source/Method_(computer_programming))") provided through the system [firmware](/source/firmware) ([UEFI](/source/UEFI) or [BIOS](/source/BIOS)), which the kernel parses. ACPI then executes the desired operations written in ''ACPI Machine Language'' (such as the initialization of hardware components) using an embedded minimal [virtual machine](/source/virtual_machine). [Intel](/source/Intel), [Microsoft](/source/Microsoft) and [Toshiba](/source/Toshiba) originally developed the standard, while [HP](/source/Hewlett-Packard), [Huawei](/source/Huawei) and [Phoenix](/source/Phoenix_Technologies) also participated later. 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](/source/Unified_EFI_Forum), in which all future development will take place.{{cite web| url = http://www.acpi.info/| title = The Advanced Configuration & Power Interface web page has a prominent note that links to the Preexisting ACPI Specifications page on the UEFI web site| date = July 23, 2014| access-date = 2016-01-25| website = acpi.org| archive-date = June 22, 2011| archive-url = https://web.archive.org/web/20110622223107/http://www.acpi.info/| url-status = dead}} {{as of|2022|10|alt=The latest version}} of the standard 6.6 was released in {{Date|2025-05-13}}.{{Cite web |author-link=UEFI Forum |date=2025-05-13 |title=Advanced Configuration and Power Interface (ACPI) Specification Release 6.6 |url=https://uefi.org/sites/default/files/resources/ACPI_Spec_6.6.pdf |access-date=2025-07-19}} == Architecture == The firmware-level ACPI has three main components: the ACPI tables, the ACPI BIOS, and the ACPI registers. The ACPI BIOS generates ACPI tables and loads ACPI tables into [main memory](/source/main_memory). Much of the firmware ACPI functionality is provided in [bytecode](/source/bytecode) of ''ACPI Machine Language'' (''AML''), a [Turing-complete](/source/Turing-complete), [domain-specific](/source/domain-specific_programming_language) [low-level language](/source/low-level_language), stored in the ACPI tables.{{cite web| url = https://os.inf.tu-dresden.de/papers_ps/tr-atare-2009.pdf| title = ATARE: ACPI Tables and Regular Expressions| author = Bernhard Kauer| date = August 2009 | access-date = 2019-02-18}} To make use of the ACPI tables, the operating system must have an [interpreter](/source/Interpreter_(computing)) for the AML bytecode. A reference AML interpreter implementation is provided by the ''ACPI Component Architecture'' (''ACPICA''). At the BIOS development time, AML bytecode is compiled from ''ACPI Source Language'' (''ASL'') code.[https://www.kernel.org/doc/ols/2005/ols2005v1-pages-59-76.pdf ACPI in Linux], 2005 === ACPI Component Architecture (ACPICA) === The '''ACPI Component Architecture''' ('''ACPICA'''), mainly written by Intel's engineers, provides an [open-source](/source/Open-source_software) platform-independent reference implementation of the operating system–related ACPI code.[http://www.acpica.org/ ACPICA: ACPI Component Architecture] The ACPICA code is used by Linux, [Haiku](/source/Haiku_(operating_system)), [ArcaOS](/source/ArcaOS){{cite web|url=https://www.arcanoae.com/wp-content/uploads/wiki/ReadMe-ACPI.txt|website=arcanoae.com|title=Readme for the ACPI Driver Package|access-date=2020-09-06}} and [FreeBSD](/source/FreeBSD),[http://www.usenix.org/events/usenix02/tech/freenix/full_papers/watanabe/watanabe.ps ACPI implementation on FreeBSD - Usenix] which supplement it with their operating-system specific code. == History == The first revision of the ACPI specification was released in December 1996, supporting 16, 24 and [32-bit](/source/32-bit) addressing spaces. It was not until August 2000 that ACPI received [64-bit](/source/64-bit) address support as well as support for multiprocessor workstations and servers with revision 2.0. In 1999, then [Microsoft](/source/Microsoft) CEO [Bill Gates](/source/Bill_Gates) stated in an e-mail that [Linux](/source/Linux) would benefit from ACPI without them having to do work and suggested to make it Windows-only.{{Cite web |title=Microsoft wollte ACPI nur für Windows |url=https://www.derstandard.at/story/2843846/microsoft-wollte-acpi-nur-fuer-windows |access-date=2022-11-06 |website=[Der Standard](/source/Der_Standard) |language=de-AT}}{{Cite web |title=Microsoft: ACPI sollte nur unter Windows funktionieren |url=https://www.golem.de/0704/51686.html |access-date=2022-11-06 |website=[Golem.de](/source/Golem.de)}}{{Cite web |last=Gates |first=Bill |date=1999-01-24 |title=ACPI extensions |url=http://www.iowaconsumercase.org/011607/3000/PX03020.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070202174648/http://www.iowaconsumercase.org/011607/3000/PX03020.pdf |archive-date=2007-02-02}} {{anchor|3.0|3.0a|3.0b}}In September 2004, revision 3.0 was released, bringing to the ACPI specification support for [SATA](/source/SATA) interfaces, [PCI Express](/source/PCI_Express) bus, [multiprocessor](/source/multiprocessor) support for more than 256 processors, [ambient light sensors](/source/ambient_light_sensors) and user-presence devices, as well as extending the thermal model beyond the previous processor-centric support. {{anchor|4.0|4.0a}}Released in June 2009, revision 4.0 of the ACPI specification added various new features to the design; most notable are the [USB 3.0](/source/USB%26nbsp%3B3.0) support, logical processor idling support, and [x2APIC](/source/x2APIC) support. {{anchor|5.0|5.0a|5.1}}Initially ACPI was exclusive to [x86](/source/x86) architecture; Revision 5.0 of the ACPI specification was released in December 2011,{{cite web | url = http://acpi.info/DOWNLOADS/ACPIspec50.pdf | title = Advanced Configuration and Power Interface Specification (Revision 5.0) | author1 = Hewlett-Packard | author1-link = Hewlett-Packard | author2 = Intel Corporation | author2-link = Intel Corporation | author3 = Microsoft | author3-link = Microsoft | author4 = Phoenix Technologies | author4-link = Phoenix Technologies | author5 = Toshiba | author5-link = Toshiba | date = 2011-12-06 | access-date = 2013-11-17 | website = acpi.info | archive-date = September 14, 2012 | archive-url = https://web.archive.org/web/20120914012029/http://www.acpi.info/DOWNLOADS/ACPIspec50.pdf | url-status = dead }} which added the [ARM architecture](/source/ARM_architecture) support. The revision 5.1 was released in July 2014.{{cite web | url = http://www.uefi.org/sites/default/files/resources/ACPI_5_1release.pdf | title = Advanced Configuration and Power Interface Specification (Revision 5.1) | date = 2014-07-23 | access-date = 2015-05-24 | website = uefi.org }} The latest revision 6.6, which was released in May 2025, added the [RISC-V](/source/RISC-V) support. == Operating systems == thumb|The "It's now safe to turn off your computer" screen in Windows 9x. Most of the computer peripherals are offline, and the only ways to exit this screen are to power off or reset the computer. thumb|The "It's now safe to turn off your computer" screen in Windows NT 4.0. Unlike Windows 9x and later NT releases, most of the essential computer peripherals are working normally, so the user can opt to restart instead of powering off their computer. thumb|The "It's now safe to power off the system" screen in Windows 10 and 11. Microsoft's [Windows 98](/source/Windows_98) was the first operating system to implement ACPI,{{Cite FTP |url=ftp://ftp.physik.hu-berlin.de/pub/driver/grafik/armada1120/RMF98/DISK1/WINDOW~1.PDF |title=Limitations When Using Microsoft Windows 98 on Compaq Armada Portables |page=3 |date=October 1998 |server=physik.hu-berlin.de |url-status=dead |access-date=2014-01-27 }}{{cite web |url=http://support.lenovo.com/en_US/guides-and-manuals/detail.page?&LegacyDocID=LWIK-3VJLL8 |archive-url=https://web.archive.org/web/20140203005405/http://support.lenovo.com/en_US/guides-and-manuals/detail.page?&LegacyDocID=LWIK-3VJLL8 |url-status=dead |archive-date=2014-02-03 |title=Windows 98 on ThinkPad systems - ThinkPad General |publisher=Support.lenovo.com |access-date=2014-01-27}} but its implementation was somewhat buggy or incomplete,{{cite book |author1=Robert Cowart |author2=Brian Knittel |title=Using Microsoft Windows 2000 Professional |url=https://archive.org/details/usingmicrosoftwi00cowa |url-access=registration |date=2000 |publisher=Que Publishing |isbn=978-0-7897-2125-9 |page=[https://archive.org/details/usingmicrosoftwi00cowa/page/30 30]}}[http://support.microsoft.com/kb/189091 Windows 98 Does Not Support ACPI Passive Cooling Mode] although some of the problems associated with it were caused by the first-generation ACPI hardware.{{cite web |archive-url=https://web.archive.org/web/19991013055230/http://winmag.com/library/1998/1201/cov0066.htm |archive-date=October 13, 1999 |website=winmag.com |url=http://winmag.com/library/1998/1201/cov0066.htm |title=Cover Story: Win98 Bugs & Fixes - December 1998 |url-status=dead}} Other operating systems, including later versions of [Windows](/source/Windows), [macOS](/source/macOS) (x86 macOS only), [eComStation](/source/eComStation), [ArcaOS](/source/ArcaOS),{{cite web |url=https://www.arcanoae.com/wp-content/uploads/wiki/ArcaOS-changes.txt |title=ArcaOS Changelog |access-date=2020-08-24}} [FreeBSD](/source/FreeBSD) (since FreeBSD 5.0{{Cite web |title=FreeBSD 5.0-RELEASE Announcement |url=https://www.freebsd.org/releases/5.0R/announce.html |access-date=2020-12-03 |website=www.freebsd.org}}), [NetBSD](/source/NetBSD) (since NetBSD 1.6{{Cite web |title=acpi(4) - NetBSD Manual Pages |url=https://man.netbsd.org/acpi.4 |access-date=2020-12-03 |website=man.netbsd.org}}), [OpenBSD](/source/OpenBSD) (since OpenBSD 3.8{{Cite web |title=acpi(4) - OpenBSD manual pages |url=https://man.openbsd.org/acpi.4 |access-date=2020-12-03 |website=man.openbsd.org}}), [HP-UX](/source/HP-UX), [OpenVMS](/source/OpenVMS), [Linux](/source/Linux), [GNU/Hurd](/source/GNU%2FHurd) and [PC](/source/IBM_PC_compatible) versions of [Solaris](/source/Solaris_(operating_system)), have at least some support for ACPI.{{cite web| title = ACPI 2.0 Specification Technical Review, Intel Developer Forum| url = http://www.acpi.info/presentations/acpi2M0800IDF.ppt| date = 2000-01-06| first = Guy | last = Therien| publisher = Intel Corporation| access-date = 2011-08-21| format = PPT| archive-url= https://web.archive.org/web/20110721184817/http://www.acpi.info/presentations/acpi2M0800IDF.ppt | archive-date=July 21, 2011 | url-status= live}} Some newer operating systems, like [Windows Vista](/source/Windows_Vista), require the computer to have an ACPI-compliant BIOS, and since [Windows 8](/source/Windows_8), the [S0ix/Modern Standby](/source/InstantGo) state was implemented.{{cite web | url = http://download.microsoft.com/download/5/b/9/5b97017b-e28a-4bae-ba48-174cf47d23cd/CPA002_WH06.ppt| format = PPT| title = ACPI in Windows Vista| first = Allen | last = Marshall| publisher = [Microsoft Corporation](/source/Microsoft_Corporation)| access-date = 2010-07-02}} Windows operating systems use acpi.sys{{cite web| title = Acpi.sys: The Windows ACPI Driver| url = https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/acpi-driver| date = 2017-06-15| publisher = [Microsoft Corporation](/source/Microsoft_Corporation)| access-date = 2019-09-20}} to access ACPI events. The 2.4 series of the Linux kernel had only minimal support for ACPI, with better support implemented (and enabled by default) from kernel version 2.6.0 onwards.[https://www.kernel.org/doc/ols/2004/ols2004v1-pages-121-132.pdf The State of ACPI in the Linux Kernel] Old ACPI BIOS implementations tend to be quite buggy, and consequently are not supported by later operating systems. For example, [Windows 2000](/source/Windows_2000), [Windows XP](/source/Windows_XP), and [Windows Server 2003](/source/Windows_Server_2003) only use ACPI if the BIOS date is after January 1, 1999.[https://msdn.microsoft.com/en-us/library/windows/hardware/ff540487(v=vs.85).aspx ACPI BIOS]. ''msdn.microsoft.com''. Similarly, Linux kernel 2.6 may not use ACPI if the BIOS date is before January 1, 2001. Linux-based operating systems can provide handling of ACPI events via acpid.{{Cite book |title=Linux in a nutshell |date=2005 |publisher=O'Reilly |last1=Siever |first1=Ellen |last2=Weber |first2=Aaron |last3=Figgins |first3=Stephen |last4=Love |first4=Robert |last5=Robbins |first5=Arnold |isbn=978-0-596-52949-9 |edition=5th |location=Sebastopol, California |page=36 |oclc=773210086}} == OSPM responsibilities == Once an OSPM-compatible operating system activates ACPI, it takes exclusive control of all aspects of power management and device configuration. The OSPM implementation must expose an ACPI-compatible environment to device drivers, which exposes certain system, device and processor states. === Power states === ==== Global states ==== The ACPI Specification defines the following four global "Gx" states and six sleep "Sx" states for an ACPI-compliant computer system:ACPI Spec Rev 5.0 - dated December 6, 2011{{cite web| url = http://www.anandtech.com/show/6355/intels-haswell-architecture/3| archive-url = https://web.archive.org/web/20121007163049/http://www.anandtech.com/show/6355/intels-haswell-architecture/3| url-status = dead| archive-date = October 7, 2012| title = Intel's Haswell Architecture Analyzed| date = 2012-10-05 | access-date = 2013-10-20| author = Anand Lal Shimpi | publisher = [AnandTech](/source/AnandTech)}} {| class="wikitable" |+ !Gx !Name !Sx !Description |- |G0 |Working |{{anchor|Away}}S0 |The computer is running and the CPU executes instructions. "Away mode" is a subset of S0, where monitor is off but background tasks are running. |- | rowspan="5" |G1 | rowspan="5" |Sleeping |{{anchor|S0ix|S0i1|S0i2|S0i3}}S0ix |[Modern Standby](/source/InstantGo),{{Cite web|url=https://docs.microsoft.com/en-gb/windows-hardware/design/device-experiences/modern-standby|title=Modern Standby|last=windows-driver-content|website=docs.microsoft.com|language=en-gb|access-date=2020-03-20}} or "Low Power S0 Idle". Partial processor SoC sleep.{{cite web |title=S0ix States |url=https://software.intel.com/en-us/energy-analysis-user-guide-s0ix-states |website=software.intel.com |language=en |date=9 March 2020}}{{cite web |last1=Wang |first1=Wendy |title=How to achieve S0ix states in Linux* |url=https://01.org/blogs/qwang59/2018/how-achieve-s0ix-states-linux |website=01.org |date=17 October 2018}} Sub states include S0i1, S0i2 and S0i3. Known to ARM and x86 devices. |- |S1 |''Power on Suspend (POS):'' The CPU stops executing instructions and enters a low‑power idle state, and the power to the RAM is maintained. Peripherals such as monitor and hard disk may be turned off. |- |S2 |CPU powered off. [CPU cache](/source/CPU_cache) is flushed to RAM. |- |S3 |Commonly referred to as ''Standby'', ''[Sleep](/source/Sleep_mode)'', or ''Suspend to RAM (STR)'': [RAM](/source/RAM) remains powered, and RAM enters self refresh mode. Most peripherals are turned off. Fans are usually turned off. Requires GPU drivers on Windows. |- |S4 | ''[Hibernation](/source/Hibernation_(computing))'' or ''Suspend to Disk:'' All content of the [main memory](/source/RAM) is saved to [non-volatile memory](/source/non-volatile_memory) such as a [hard drive](/source/hard_drive), and the system is powered down. |- |G2 |Soft Off |S5 | ''[Shutdown](/source/Shutdown_(computing)):'' system is powered down. |- |G3 |Mechanical Off | |The computer's power has been totally removed via a mechanical switch (as on the rear of a PSU). The power cord can be removed and the system is safe for disassembly (typically, only the [real-time clock](/source/real-time_clock) continues to run using its own small battery). |} {{anchor|Legacy}}The specification also defines a ''Legacy'' state: the state of an operating system which does not support ACPI. In this state, the hardware and power are not managed via ACPI, effectively disabling ACPI. ==== Device states ==== The device states ''D0''–''D3'' are device dependent: * ''D0'' or ''Fully On'' is the operating state. ** As with S0ix, Intel has ''D0ix'' states for intermediate levels on the SoC.{{cite web |title=D0ix States |url=https://software.intel.com/en-us/energy-analysis-user-guide-d0ix-states |website=software.intel.com |language=en |date=9 March 2020}} * ''D1'' and ''D2'' are intermediate power-states whose definition varies by device. * ''D3'': The D3 state is further divided into ''D3 Hot'' (has auxiliary power), and ''D3 Cold'' (no power provided): ** ''Hot'': A device can assert power management requests to transition to higher power states. ** ''Cold'' or ''Off'' has the device powered off and unresponsive to its bus. === Processor states === The CPU power states ''C0''–''C3'' are defined as follows: * ''C0'' is the operating state. * ''C1'' (often known as ''Halt'') is a state where the processor is not executing instructions, but can return to an executing state essentially instantaneously. All ACPI-conformant processors must support this power state. Some processors, such as the [Pentium 4](/source/Pentium_4) and [AMD Athlon](/source/AMD_Athlon), also support an Enhanced C1 state (''C1E'' or Enhanced Halt State) for lower power consumption, however this proved to be buggy on some systems.{{cite web|title=Athlon II X2: Hardware C1E and Return of the CnQ Bug| publisher = [AnandTech](/source/AnandTech)|url=https://www.anandtech.com/show/2775/2|archive-url=https://web.archive.org/web/20100419120817/http://www.anandtech.com/show/2775/2|url-status=dead|archive-date=April 19, 2010|access-date=2020-10-26}}{{cite web| title = Intel's Pentium 4 600 series processors| first = Scott | last = Wasson| date = 2005-02-21| page = 2| publisher = [The Tech Report](/source/The_Tech_Report)| url = http://techreport.com/articles.x/7998/2}} * ''C2'' (often known as ''Stop-Clock'') is a state where the processor maintains all software-visible state, but may take longer to wake up. This processor state is optional. * ''C3'' (often known as ''Sleep'') is a state where the processor does not need to keep its [cache coherent](/source/Cache_coherence), but maintains other state. Some processors have variations on the C3 state (Deep Sleep, Deeper Sleep, etc.) that differ in how long it takes to wake the processor. This processor state is optional. ''Additional states'' are defined by manufacturers for some processors. They are reported to the system via the {{tt|_CST}} method.{{cite web | title=8.1. Processor Power States — ACPI Specification 6.4 documentation | url=https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/08_Processor_Configuration_and_Control/processor-power-states.html }} For example, [Intel](/source/Intel)'s [Haswell](/source/Haswell_(microarchitecture)) platform has states up to ''C10'', where it distinguishes ''core'' states and ''package'' states: the difference being that the ''package'' not only includes the processor cores, but also components such as the L3 cache, memory controller, and other I/O functions.{{cite web| url = http://images.anandtech.com/reviews/cpu/intel/Haswell/ULT/c10.png| archive-url = https://web.archive.org/web/20130927220948/http://images.anandtech.com/reviews/cpu/intel/Haswell/ULT/c10.png| url-status = dead| archive-date = September 27, 2013| title = Processor Package and Core C-States| date = 2013-06-09 | access-date = 2013-10-20| publisher = [AnandTech](/source/AnandTech)}} Similarly, AMD [Zen 2](/source/Zen_2) CPUs diffentiate between C-states and P-states for the Core Complex and the Infinity Fabric.{{cite web |title=[Public] TUNING GUIDE AMD EPYC 9004 BIOS & Workload |url=https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/tuning-guides/58011-epyc-9004-tg-bios-and-workload.pdf}} For describing the idle states of groupings of components (e.g. a package containing several cores), the {{tt|_LPI}} (low power idle) method is used.{{cite web |title=8.4. Declaring Processors — ACPI Specification 6.4 documentation |url=https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/08_Processor_Configuration_and_Control/declaring-processors.html#lpi-low-power-idle-states |website=uefi.org}} This should not be confused with Intel's private {{tt|LPIT}} table, used to describe S0ix sleep in package C10 or PCH SLP_S0 state.{{cite web |title=Low Power Idle Table (LPIT) — The Linux Kernel documentation |url=https://docs.kernel.org/firmware-guide/acpi/lpit.html |website=docs.kernel.org}} === Performance state === While a device or processor operates (D0 and C0, respectively), it can be in one of several [power-performance states](/source/Dynamic_voltage_scaling). These states are implementation-dependent. P0 is always the highest-performance state, with P1 to P''n'' being successively lower-performance states. The total number of states is device or processor dependent, but can be no greater than 16.{{cite web| url = http://www.acpi.info/DOWNLOADS/ACPIspec30.pdf| title = Advanced Configuration and Power Interface Specification, Revision 3.0, Section 2.6 Device and Processor Performance State Definitions| date = 2004-09-02| access-date = 2015-08-19| website = ACPI.info| page = 23| archive-date = November 28, 2015| archive-url = https://web.archive.org/web/20151128143452/http://www.acpi.info/DOWNLOADS/ACPIspec30.pdf| url-status = dead}} P-states have become known as [SpeedStep](/source/SpeedStep) in [Intel](/source/Intel) processors, as [PowerNow!](/source/PowerNow!) or [Cool'n'Quiet](/source/Cool'n'Quiet) in [AMD](/source/Advanced_Micro_Devices) processors, and as [PowerSaver](/source/PowerSaver) in [VIA](/source/VIA_Technologies) processors. * ''P0'' maximum power and frequency * ''P1'' less than ''P0'', voltage and frequency scaled * ''P2'' less than ''P1'', voltage and frequency scaled[Link aggregation](/source/Link_aggregation) * ''Pn'' less than ''P(n–1)'', voltage and frequency scaled See {{section link|Dynamic frequency scaling|Autonomous frequency scaling}} for a brief description of a newer control method based on the ACPI Collaborative Processor Performance Control (CPPC). This new method allows hundreds of possible states, and for the processor to autonomously to choose from a given range of states. == Interfaces == === Hardware === ACPI-compliant systems interact with hardware through either a "Function Fixed Hardware (FFH) Interface", or a platform-independent hardware programming model which relies on platform-specific ACPI Machine Language (AML) provided by the [original equipment manufacturer](/source/original_equipment_manufacturer) (OEM). Function Fixed Hardware interfaces are platform-specific features, provided by platform manufacturers for the purposes of performance and failure recovery. Standard [Intel](/source/Intel)-based [PCs](/source/IBM_PC_Compatible) have a fixed function interface defined by Intel,{{cite web| url = ftp://download.intel.com/technology/iapc/acpi/downloads/30222305.pdf| title = Intel Processor Vendor-Specific ACPI| author = Intel Corporation| author-link = Intel Corporation| date = September 2006| archive-url = https://web.archive.org/web/20070118021711/http://download.intel.com:80/technology/IAPC/acpi/downloads/30222305.pdf| archive-date = 2007-01-18| url-status = dead| access-date = 2014-10-05}} which provides a set of core functionality that reduces an ACPI-compliant system's need for full driver stacks for providing basic functionality during boot time or in the case of major system failure. ACPI Platform Error Interface (APEI) is a specification for reporting of hardware errors, e.g. chipset, RAM to the operating system. === Firmware === ACPI defines many tables that provide the interface between an ACPI-compliant [operating system](/source/operating_system) and system firmware ([BIOS](/source/BIOS) or [UEFI](/source/UEFI)). This includes RSDP, RSDT, XSDT, FADT, FACS, DSDT, SSDT, MADT, and MCFG, for example. {{cite journal | citeseerx = 10.1.1.173.2206 | title = ACPI in Linux | first = Len | last = Brown | date = 2005-07-20 | journal = Ottawa Linux Symposium | page = 3 }} {{Cite web|title=ACPI Tables — The Linux Kernel documentation|url=https://www.kernel.org/doc/html/latest/arm64/acpi_object_usage.html|access-date=2020-11-08|website=www.kernel.org|archive-date=October 20, 2020|archive-url=https://web.archive.org/web/20201020091509/https://www.kernel.org/doc/html/latest/arm64/acpi_object_usage.html|url-status=dead}} The tables allow description of system hardware in a platform-independent manner, and are presented as either fixed-formatted data structures or in AML. The main AML table is the DSDT (differentiated system description table). The AML can be decompiled by tools like Intel's iASL (open-source, part of ACPICA) for purposes like patching the tables for expanding OS compatibility.{{cite web |title=DSDT |url=https://wiki.archlinux.org/index.php/DSDT |website=ArchWiki}}{{cite web |title=Getting Started With ACPI|url=https://khronokernel.github.io/Getting-Started-With-ACPI/ |website=GitBook}} The Root System Description Pointer (RSDP) is located in a platform-dependent manner, and describes the rest of the tables. A custom ACPI table called the Windows Platform Binary Table (WPBT) is used by Microsoft to allow vendors to add software into the Windows OS automatically. [Lenovo](/source/Lenovo) have been caught using this feature to install harmful software such as [Superfish](/source/Superfish).{{cite web |last1=Hoffman |first1=Chris |date=August 19, 2015 |title=Zombie Crapware: How the Windows Platform Binary Table Works |url=https://www.howtogeek.com/226308/the-windows-platform-binary-table-why-crapware-can-come-back-after-a-clean-install/ |website=How-To Geek}} Also, [Gigabyte Technology](/source/Gigabyte_Technology) have been found using this feature to install its OEM software. [Samsung](/source/Samsung) shipped PCs with Windows Update disabled. Windows versions older than Windows 7 do not support this feature, but alternative techniques can be used. This behavior has been compared to [rootkit](/source/rootkit)s.{{cite web |title=Vendors 'rootkit': 'Windows Platform Binary Table' (WPBT) |url=https://borncity.com/win/2017/12/06/vendors-rootkit-windows-platform-binary-table-wpbt/ |website=Born's Tech and Windows World |date=December 6, 2017}}{{Cite web |author1=Mayank Sharma |date=2021-09-27 |title=Millions of Windows 10 PCs exposed by nasty security vulnerability |url=https://www.techradar.com/news/nasty-security-vulnerability-exposes-millions-of-windows-10-pcs |access-date=2022-11-10 |website=[TechRadar](/source/TechRadar) |language=en}} == Criticism == [Ubuntu](/source/Ubuntu) founder [Mark Shuttleworth](/source/Mark_Shuttleworth) says ACPI is a security risk.Mark Shuttleworth blog (March 17, 2014), [http://www.markshuttleworth.com/archives/1332 "ACPI, firmware and your security"] He says "arguing for ACPI on your next-generation device is arguing for a trojan horse of monumental proportions to be installed in your living room and in your data centre" and "firmware on your device is the [NSA](/source/NSA)'s best friend". He goes on to say, "Your biggest mistake is to assume that the NSA is the only institution abusing this position of trust – in fact, it's reasonable to assume that all firmware is a cesspool of insecurity, courtesy of incompetence of the highest degree from manufacturers, and competence of the highest degree from a very wide range of such agencies." He suggests [open-source](/source/open-source), [declarative](/source/declarative_programming) firmware (ACPI or non-ACPI) as a solution.Linux Magazine issue 162, May 2014, page 9 In November 2003, [Linus Torvalds](/source/Linus_Torvalds)—author of the [Linux kernel](/source/Linux_kernel)—described ACPI as "a complete design disaster in every way".Linux Magazine issue 162, May 2014, page 9{{cite web |last=Searls |first=Doc |date=2003-11-25 |title=Linus & the Lunatics, Part II |url=http://www.linuxjournal.com/article/7279 |access-date=2010-01-13 |publisher=Linux Journal}} == See also == * [Active State Power Management](/source/Active_State_Power_Management) * [Coreboot](/source/Coreboot) * [Devicetree](/source/Devicetree) * [Green computing](/source/Green_computing) * [Power management keys](/source/Power_management_keys) * [Server Base System Architecture](/source/Server_Base_System_Architecture) (SBSA) * [Wake-on-LAN](/source/Wake-on-LAN) == Further reading == * {{cite web|url=https://mjg59.dreamwidth.org/68350.html|title=Why ACPI?|first1=Matthew|last1=Garrett|author-link=Matthew Garrett|date=2023-10-31}} == References == {{Reflist}} == External links == * {{Official website|https://uefi.org/specifications}} (UEFI and ACPI specifications) * [http://www.hardwaresecrets.com/everything-you-need-to-know-about-the-cpu-c-states-power-saving-modes/ Everything You Need to Know About the CPU C-States Power Saving Modes] *[http://www.virtualbox.org/svn/vbox/trunk/src/VBox/Devices/EFI/Firmware/OvmfPkg/AcpiTables/ Sample EFI ASL code] {{Webarchive|url=https://web.archive.org/web/20230412142524/http://www.virtualbox.org/svn/vbox/trunk/src/VBox/Devices/EFI/Firmware/OvmfPkg/AcpiTables/ |date=April 12, 2023 }} used by [VirtualBox](/source/VirtualBox); EFI/ASL code itself is from the open source Intel EFI Development Kit II ([TianoCore](/source/Tianocore)) * [https://acpica.org ACPICA] {{Firmware and booting}}{{Computer processor power management technologies}} {{CPU technologies}} {{DEFAULTSORT:Advanced Configuration And Power Interface}} Category:BIOS Category:Unified Extensible Firmware Interface Category:Application programming interfaces Category:Computer hardware standards Category:Open standards Category:Electric power Category:System administration --- Adapted from the Wikipedia article [ACPI](https://en.wikipedia.org/wiki/ACPI) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/ACPI?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.