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Concept
Dynamic frequency scaling
Summary
Dynamic frequency scaling (also known as CPU throttling) is a power management technique in computer architecture whereby the frequency of a microprocessor can be automatically adjusted "on the fly" depending on the actual needs, to conserve power and reduce the amount of heat generated by the chip. Dynamic frequency scaling helps preserve battery on mobile devices and decrease cooling cost and noise on quiet computing settings, or can be useful as a security measure for overheated systems (e.g. after poor overclocking).
Dynamic frequency scaling almost always appear in conjunction with dynamic voltage scaling, since higher frequencies require higher supply voltages for the digital circuit to yield correct results. The combined topic is known as dynamic voltage and frequency scaling (DVFS).
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.
Processor power dissipation#Sources
The dynamic power (switching power) dissipated by a chip is C·V2·A·f, where C is the capacitance being switched per clock cycle, V is voltage, A is the Activity Factor indicating the average number of switching events per clock cycle by the transistors in the chip (as a unitless quantity) and f is the clock frequency.
Voltage is therefore the main determinant of power usage and heating. The voltage required for stable operation is determined by the frequency at which the circuit is clocked, and can be reduced if the frequency is also reduced. Dynamic power alone does not account for the total power of the chip, however, as there is also static power, which is primarily because of various leakage currents. Due to static power consumption and asymptotic execution time it has been shown that the energy consumption of software shows convex energy behavior, i.e., there exists an optimal CPU frequency at which energy consumption is minimized.
Official source
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