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The efficiency of some electrical components, such as voltage regulators, decreases with increasing temperature, so the power usage may increase with temperature. Since increasing power use may increase the temperature, increases in voltage or frequency may increase system power demands even further than the CMOS formula indicates, and vice versa.<ref>{{cite web | url = http://www.silentpcreview.com/article821-page5.html | title = Asus EN9600GT Silent Edition Graphics Card | author = Mike Chin | page = 5 | work = Silent PC Review | access-date = 21 April 2008}}</ref><ref name="SPCRNewLevels">{{cite web | url = http://www.silentpcreview.com/article814-page1.html | title = 80 Plus expands podium for Bronze, Silver & Gold | author = Mike Chin | work = Silent PC Review | date = 19 March 2008 | access-date = 21 April 2008 }}</ref>
== Standard interface ==
[[ACPI]] 1.0 (1996) defines a way for a CPU to go to idle "C states", but defines no frequency-scaling system.
ACPI 2.0 (2000) introduces a system of ''P states'' (power-performance states) that a processor can use to communicate its possible frequency–power settings to the OS. The operating system then sets the speed as needed by switching between these states. SpeedStep, PowerNow!/Cool'n'Quiet, and PowerSaver all work through P states.<ref>{{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
}}</ref>
ACPI 5.0 (2011) introduces collaborative processor performance control (CPPC). Instead of asking for a specific performance level, the OS only sends a hint of reletaive performance/power preference, leaving the CPU to do its own frequency selection. Windows and Linux offer support for CPPC on newer AMD and Intel CPUs.<ref>{{cite web |title=Collaborative Processor Performance Control (CPPC) — The Linux Kernel documentation |url=https://www.kernel.org/doc/html/latest/admin-guide/acpi/cppc_sysfs.html |website=www.kernel.org}}</ref><ref>{{cite web |title=Overview about power and performance tuning for the Windows Server |url=https://learn.microsoft.com/en-us/windows-server/administration/performance-tuning/hardware/power/power-performance-tuning |website=learn.microsoft.com |language=en-us |date=29 August 2022}}</ref>
==Performance impact==
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