Editing Processor power dissipation (section)

== Power management ==
{{See also|Variable TDP}}
Designing CPUs that perform tasks [[Energy conversion efficiency|efficiently]] without [[thermal shock|overheating]] is a major consideration of nearly all CPU manufacturers to date. Historically, early CPUs implemented with [[vacuum tube]]s consumed power on the order of many [[kilowatt]]s. Current CPUs in general-purpose [[personal computer]]s, such as [[desktop computer|desktop]]s and [[laptop]]s, consume power in the order of tens to hundreds of watts. Some other CPU implementations use very little power; for example, the CPUs in [[mobile phone]]s often use just a few [[watt]]s of electricity,<ref>{{cite report |url=https://www.microsoft.com/en-us/research/publication/accurate-cpu-power-modeling-for-multicore-smartphones/ |title=Accurate CPU Power Modeling for Multicore Smartphones |first1=Yifan |last1=Zhang |first2=Yunxin |last2=Liu |first3=Li |last3=Zhuang |first4=Xuanzhe |last4=Liu |first5=Feng |last5=Zhao |first6=Qun |last6=Li |publisher=Microsoft Research |id=MSR-TR-2015-9}}</ref> while some [[microcontroller]]s used in [[embedded system]]s may consume only a few milliwatts or even as little as a few microwatts.

There are a number of engineering reasons for this pattern:
* For a given CPU core, energy usage will scale up as its clock rate increases. Reducing the clock rate or [[undervolting]] usually reduces energy consumption; it is also possible to undervolt the microprocessor while keeping the clock rate the same.<ref>{{cite web |url=http://www.anandtech.com/show/5763/undervolting-and-overclocking-on-ivy-bridge |title=Undervolting and Overclocking on Ivy Bridge |first=Ian |last=Cutress |website=anandtech.com |date=2012-04-23}}</ref>
* New features generally require more [[transistor]]s, each of which uses power. Turning unused areas off saves energy, such as through [[clock gating]].
* As a processor model's design matures, smaller transistors, lower-voltage structures, and design experience may reduce energy consumption.

Processor manufacturers usually release two power consumption numbers for a CPU:
* ''typical thermal power'', which is measured under normal load (for instance, AMD's [[average CPU power]])
* ''maximum thermal power'', which is measured under a worst-case load

For example, the Pentium 4 2.8&nbsp;GHz has a 68.4&nbsp;W typical thermal power and 85&nbsp;W maximum thermal power. When the CPU is idle, it will draw far less than the typical thermal power. [[Datasheet]]s normally contain the [[thermal design power]] (TDP), which is the maximum amount of [[heat]] generated by the CPU, which the [[computer cooling|cooling system]] in a computer is required to [[dissipation|dissipate]].  Both Intel and [[Advanced Micro Devices]] (AMD) have defined TDP as the maximum heat generation for thermally significant periods, while running worst-case non-synthetic workloads; thus, TDP is not reflecting the actual maximum power of the processor.  This ensures the computer will be able to handle essentially all applications without exceeding its thermal envelope, or requiring a cooling system for the maximum theoretical power (which would cost more but in favor of extra headroom for processing power).<ref>{{cite web |url=http://www.silentpcreview.com/article169-page3.html |title=Athlon 64 for Quiet Power |page=3 |date=2004-06-15 |access-date=2013-12-21 |first=Mike |last=Chin |website=silentpcreview.com |quote=Thermal Design Power (TDP) should be used for processor thermal solution design targets. The TDP is not the maximum power that the processor can dissipate.}}</ref><ref>{{cite news |url=https://arstechnica.com/gadgets/2013/01/the-technical-details-behind-intels-7-watt-ivy-bridge-cpus/ |first=Andrew |last=Cunningham |title=The technical details behind Intel's 7 Watt Ivy Bridge CPUs |date=2013-01-14 |access-date=2013-01-14 |work=Ars Technica|quote = In Intel's case, a specified chip's TDP has less to do with the amount of power a chip needs to use (or can use) and more to do with the amount of power the computer's fan and heatsink need to be able to dissipate while the chip is under sustained load. Actual power usage can be higher or (much) lower than TDP, but the figure is intended to give guidance to engineers designing cooling solutions for their products.}}</ref>

In many applications, the CPU and other components are idle much of the time, so idle power contributes significantly to overall system power usage.  When the CPU uses [[power management]] features to reduce energy use, other components, such as the motherboard and chipset, take up a larger proportion of the computer's energy. In applications where the computer is often heavily loaded, such as scientific computing, [[performance per watt]] (how much computing the CPU does per unit of energy) becomes more significant.

CPUs typically use a significant portion of the power consumed by the [[computer]]. Other major uses include fast [[video card]]s, which contain [[graphics processing unit]]s, and [[Power supply unit (computer)|power supplies]]. In laptops, the [[LCD]]'s backlight also uses a significant portion of overall power. While [[power management|energy-saving feature]]s have been instituted in personal computers for when they are idle, the overall consumption of today's high-performance CPUs is considerable. This is in strong contrast with the much lower energy consumption of CPUs designed for low-power devices.