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Processor throttling is also known as "automatic [[underclocking]]". Automatic [[overclocking]] (boosting) is also technically a form of dynamic frequency scaling, but it's relatively new and usually not discussed with throttling.
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{{see also|Processor power dissipation#Sources}}
The dynamic power (''[[switching power]]'') dissipated per unit of time by a chip is ''C·V<sup>2</sup>·A·f'', where C is the [[capacitance]] being switched per clock cycle, V is [[voltage]], A is the Activity Factor<ref name="ActivityFactor">{{cite journal | title = Timing-aware power-optimal ordering of signals | author = K. Moiseev, A. Kolodny and S. Wimer | journal = ACM Transactions on Design Automation of Electronic Systems |volume=13 |issue=4 |date=September 2008| pages = 1–17 | doi = 10.1145/1391962.1391973 }}</ref> indicating the average number of switching events undergone by the transistors in the chip (as a unit-less quantity) and f is the switching frequency.<ref>{{Cite book|first=J. M.|last= Rabaey|title= Digital Integrated Circuits|publisher= Prentice Hall|year= 1996}}</ref>
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One major difference between the two is that in modern PC systems overclocking is mostly done over the [[Front Side Bus]] (mainly because the multiplier is normally locked), but dynamic frequency scaling is done with the [[CPU multiplier|multiplier]]. Moreover, overclocking is often static, while dynamic frequency scaling is always dynamic. Software can often incorporate overclocked frequencies into the frequency scaling algorithm, if the chip degradation risks are allowable.
==Support across vendors==
[[Intel]]'s CPU throttling technology, [[SpeedStep]], is used in its mobile and desktop CPU lines.▼
=== Intel ===
▲[[Intel]]'s CPU throttling technology, [[SpeedStep]], is used in its mobile and desktop CPU lines.
=== AMD ===
[[AMD]] employs two different CPU throttling technologies. AMD's [[Cool'n'Quiet]] technology is used on its desktop and server processor lines. The aim of Cool'n'Quiet is not to save battery life, as it is not used in AMD's mobile processor line, but instead with the purpose of producing less heat, which in turn allows the system fan to spin down to slower speeds, resulting in cooler and quieter operation, hence the name of the technology. AMD's [[PowerNow!]] CPU throttling technology is used in its mobile processor line, though some supporting CPUs like the [[AMD K6-2]]+ can be found in desktops as well.
[[AMD PowerTune]] and [[AMD ZeroCore Power]] are dynamic frequency scaling technologies for [[Graphics processing unit|GPUs]].▼
=== VIA Technologies ===
[[VIA Technologies]] processors use a technology named [[LongHaul]] (PowerSaver), while [[Transmeta]]'s version was called [[LongRun]].
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According to the [[Advanced Configuration and Power Interface|ACPI]] Specs, the C0 working state of a modern-day CPU can be divided into the so-called "P"-states (performance states) which allow clock rate reduction and "T"-states (throttling states) which will further throttle down a CPU (but not the actual clock rate) by inserting STPCLK (stop clock) signals and thus omitting duty cycles.
▲[[AMD PowerTune]] and [[AMD ZeroCore Power]] are dynamic frequency scaling technologies for [[Graphics processing unit|GPUs]].
== See also ==
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