View source for SpeedStep

{{Use American English|date=September 2024}}
{{Use mdy dates|date=September 2024}}
{{Infobox computer hardware
| name = Intel Enhanced SpeedStep Technology
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| designfirm = [[Intel]]
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| introduced = Q1 2005<ref name="Pentium 4 660 specs" />
| discontinued = 
| type = [[Dynamic frequency scaling]]
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}}

'''Enhanced SpeedStep''' is a series of [[dynamic frequency scaling]] technologies (codenamed '''Geyserville'''<ref>{{cite web |last=Larabel |first=Michael |author-link=Michael Larabel |date=February 16, 2006 |title=Intel EIST SpeedStep |publisher=[[Phoronix|Phoronix Media]] |url=https://www.phoronix.com/scan.php?page=article&item=397&num=1 |access-date=August 9, 2010 }}</ref> and including SpeedStep, '''SpeedStep II''', and '''SpeedStep III''') built into some [[Intel]]'s [[microprocessor]]s that allow the [[clock speed]] of the processor to be dynamically changed (to different ''P-states'') by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizing [[CPU power dissipation|power draw and heat generation]]. EIST (SpeedStep III) was introduced in several Prescott 6 series in the first quarter of 2005, namely the [[Pentium 4]] 660.<ref name="Pentium 4 660 specs">{{Cite web |date=2005 |title=Intel Pentium 4 Processor 660 Supporting HT Technology |url=https://www.intel.com/content/www/us/en/products/sku/27484/intel-pentium-4-processor-660-supporting-ht-technology-2m-cache-3-60-ghz-800-mhz-fsb/specifications.html |url-status=live |archive-url=https://web.archive.org/web/20240424210459/https://ark.intel.com/content/www/us/en/ark/products/27484/intel-pentium-4-processor-660-supporting-ht-technology-2m-cache-3-60-ghz-800-mhz-fsb.html |archive-date=April 24, 2024 |access-date=December 10, 2024 |website=intel.com |publisher=[[Intel]]}}</ref> Intel Speed Shift Technology (SST) was introduced in Intel [[Skylake microarchitecture|Skylake]] Processor.<ref>{{Cite web |last=Howse |first=Brett |title=Examining Intel's New Speed Shift Tech on Skylake: More Responsive Processors |url=https://www.anandtech.com/show/9751/examining-intel-skylake-speed-shift-more-responsive-processors |website=anandtech.com |access-date=June 26, 2020 }}</ref>

'''Enhanced Intel SpeedStep Technology''' is sometimes abbreviated as '''EIST'''. Intel's trademark of "Intel SpeedStep" was canceled due to the trademark being invalidated in 2012.<ref>{{Cite web |url=https://tsdr.uspto.gov/#caseNumber=2497572&caseType=US_REGISTRATION_NO&searchType=statusSearch |title=Trademark Status & Document Retrieval |website=tsdr.uspto.gov |access-date=April 26, 2020 }}</ref>

==Explanation==
{{More citations needed section|date=December 2016}}

Running a processor at high clock speeds allows for better performance. However, when the same processor is run at a lower frequency (speed), it generates less heat and consumes less power. In many cases, the [[CPU core voltage|core voltage]] can also be reduced, further reducing power consumption and heat generation. By using SpeedStep, users can select the balance of power conservation and performance that best suits them, or even change the clock speed dynamically as the processor burden changes.

The power consumed by a CPU with a [[capacitance]] ''C'', running at frequency ''f'' and voltage ''V'' is approximately:<ref>{{cite web |title=Enhanced Intel SpeedStep Technology for the Intel Pentium M Processor - White Paper |publisher=[[Intel]] |date=March 2004 |url=http://download.intel.com/design/network/papers/30117401.pdf |archive-url=https://web.archive.org/web/20150812030010/http://download.intel.com/design/network/papers/30117401.pdf |archive-date=August 12, 2015 |url-status=live |access-date=September 1, 2024 }}</ref>
: <math>P = C V^2 f</math>

For a given processor, ''C'' is a fixed value. However, ''V'' and ''f'' can vary considerably. For example, for a 1.6&nbsp;GHz [[Pentium M]], the clock frequency can be stepped down in 200&nbsp;MHz decrements over the range from 1.6 to 0.6&nbsp;GHz. At the same time, the voltage requirement decreases from 1.484 to 0.956&nbsp;V. The result is that the power consumption theoretically goes down by a factor of 6.4. In practice, the effect may be smaller because some CPU instructions use less energy per tick of the CPU clock than others. For example, when an operating system is not busy, it tends to issue [[x86]] halt ([[HLT (x86 instruction)|HLT]]) instructions, which suspend operation of parts of the CPU for a time period, so it uses less energy per tick of the CPU clock than when executing productive instructions in its normal state. For a given rate of work, a CPU running at a higher clock rate will execute a greater proportion of HLT instructions. The simple equation which relates power, voltage and frequency above also does not take into account the static power consumption of the CPU. This tends not to change with frequency, but does change with temperature and voltage.

{{See also|Processor power dissipation#Sources}}

==Known issues==
Microsoft has reported that there may be problems previewing video files when SpeedStep (or the AMD equivalent [[PowerNow!]]) is enabled under Windows 2000 or Windows XP.<ref>{{cite web |title=PRB: Poor Performance When You Preview Video |url=http://support.microsoft.com/kb/318682/EN-US/ |publisher=[[Microsoft]] |archive-url=https://web.archive.org/web/20140827054313/http://support.microsoft.com/kb/318682/EN-US/ |archive-date=August 27, 2014 }}</ref>

==Operating system support==
* [[Solaris (operating system)|Solaris]] has supported SpeedStep since [[OpenSolaris]] SXDE 9/07.<ref>{{cite web |title=Introducing Enhanced Intel SpeedStep to Solaris |publisher=[[Sun Microsystems]] |url=https://blogs.oracle.com/mhaywood/entry/introducing_speedstep_on_solaris |access-date=March 24, 2008 }}</ref>
* Older versions of Microsoft Windows, [[Windows 2000]] and earlier, need a special driver and dashboard application to access the SpeedStep feature. Intel's website specifically states that such drivers ''must'' come from the computer manufacturer; there are no generic drivers supplied by Intel which will enable SpeedStep for older Windows versions if one cannot obtain a manufacturer's driver.<ref>{{cite web |title=Processors - Update the Driver for Intel SpeedStep Technology |publisher=[[Intel]] |date=January 17, 2007 |url=http://www.intel.com/support/processors/sb/cs-003772.htm |access-date=April 30, 2007 }}</ref><ref>{{cite web |title=Mobile Intel Pentium 4 Processors - M - Enhanced Intel SpeedStep Technology |publisher=[[Intel]] |date=July 6, 2006 |url=http://www.intel.com/support/processors/mobile/pentium4/sb/CS-007499.htm |access-date=April 30, 2007 }}</ref>
* Under Microsoft [[Windows XP]], SpeedStep support is built into the power management console under the control panel. In Windows XP a user can regulate processor speed indirectly by changing power schemes. The "Home/Office Desk" setting disables SpeedStep on AC power, the "Portable/Laptop" power scheme enables SpeedStep, and the "Max Battery" uses SpeedStep to slow the processor to minimal power levels as the battery weakens.<ref>{{cite web |title=Intel SpeedStep, Windows XP, and confusing Power Profiles |first=Michael |last=Chu |url=http://www.orthogonalthought.com/blog/index.php/2007/09/intel-speedstep-windows-xp-and-confusing-power-profiles/ |access-date=March 10, 2009 }}</ref><ref>{{cite web |title=Runtime Power Management |url=https://h10032.www1.hp.com/ctg/Manual/c00465840.pdf |edition=v1.0 |publisher=[[Hewlett-Packard]] |access-date=September 1, 2024 }}</ref> The SpeedStep settings for power schemes, either built-in or custom, cannot be modified from the control panel's GUI, but can be modified using the <code>powercfg.exe</code> command-line utility.<ref>{{cite web |title=Powercfg Command-Line Options |date=July 25, 2008 |publisher=[[Microsoft]] |url=https://technet.microsoft.com/en-us/library/cc748940.aspx |access-date=June 11, 2009 }}</ref>
* The [[Linux kernel]] has a subsystem called "cpufreq", tunable by power-scheme and command line, devoted to the control of the operating frequency and voltage of a CPU.  Linux runs on Intel, AMD, and other makes of CPU.<ref>{{cite web |last=Wysocki |first=Rafael J. |date=2017 |url=https://www.kernel.org/doc/html/latest/admin-guide/pm/cpufreq.html |title=CPU Performance Scaling |publisher=[[Linux Kernel Organization]] |access-date=September 1, 2024 }}</ref><ref>{{cite web |url=https://www.kernel.org/doc/Documentation/cpu-freq/amd-powernow.txt |title=PowerNow! Cool'n'Quiet }}</ref>
* Newer version [[Windows 10]] and [[Linux kernel]] support Intel Speed Shift Technology.

In contrast, AMD has supplied and supported drivers for its competing [[PowerNow!]] technology that work on Windows 2000, ME, 98, and NT.<ref>{{cite web |title=AMD Turion 64 X2 Dual-Core Mobile Technology Utilities & Updates |url=https://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_871_14098,00.html |publisher=[[Advanced Micro Devices]] |access-date=April 30, 2007 }}</ref><ref>{{cite web |title=AMD Turion 64 Mobile Technology Utilities & Updates |url=https://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_1202_1073%5E871%5E13349,00.html |publisher=Advanced Micro Devices |access-date=April 30, 2007 }}</ref>

==See also==
* {{Annotated link|Advanced Configuration and Power Interface}}
* {{Annotated link|AMD PowerTune}}
* {{Annotated link|AMD Turbo Core}}
* {{Annotated link|Cool'n'Quiet}}
* {{Annotated link|CPU-Z}}
* {{Annotated link|Intel Turbo Boost}}
* {{Annotated link|Power management}}

==References==
{{Reflist}}

{{Intel technology}}
{{Computer processor power management technologies}}

[[Category:Clock signal]]
[[Category:Computer hardware tuning]]
[[Category:Intel microprocessors]]
[[Category:X86 architecture]]