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Central processing unit power dissipation or CPU power dissipation is the process in which central processing units (CPUs) consume electrical energy, and dissipate this energy both by the action of the switching devices contained in the CPU (such as transistors or vacuum tubes) and by the energy lost in the form of heat due to the impedance of the electronic circuits. == Power management == Designing CPUs that perform tasks efficiently without overheating is a major consideration of nearly all CPU manufacturers to date. Some CPU implementations use very little power; for example, the CPUs in mobile phones often use just a few hundred milliwatts of electricity, while some microcontrollers used in embedded systems may consume only a few milliwatts or even as little as a few microwatts. In comparison, CPUs in general-purpose personal computers, such as desktops and laptops, dissipate significantly more power because of their higher complexity and speed. These microelectronic CPUs may consume power in the order of a few watts to hundreds of watts. Historically, early CPUs implemented with vacuum tubes consumed power on the order of many kilowatts. CPUs for desktop computers typically use a significant portion of the power consumed by the computer. Other major uses include fast video cards, which contain graphics processing units,〔Mittal et al., "(A Survey of Methods for Analyzing and Improving GPU Energy Efficiency )", ACM Computing Surveys, 2014.〕 and power supplies. In laptops, the LCD's backlight also uses a significant portion of overall power. While energy-saving features 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. One such CPU, the Intel XScale, can run at 600 MHz consuming under 1 W of power, whereas Intel x86 PC processors in the same performance bracket consume a few times more energy. There are some engineering reasons for this pattern. * For a given device, operating at a higher clock rate may require more power. 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.〔(【引用サイトリンク】title=Undervolting and Overclocking on Ivy Bridge )〕 * New features generally require more transistors, 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 GHz has 68.4 W typical thermal power and 85 W maximum thermal power. When the CPU is idle, it will draw far less than the typical thermal power. Datasheets normally contain the thermal design power (TDP), which is the maximum amount of heat generated by the CPU, which the cooling system in a computer is required to 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). 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「CPU power dissipation」の詳細全文を読む スポンサード リンク
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