Fan control is the management of the rotational speed of an electric fan. In computers, various types of computer fans are used to provide adequate cooling, and different fan control mechanisms balance their cooling capacities and noise they generate. This is commonly accomplished by the motherboards having hardware monitoring circuitry, which can be configured by the end-user through BIOS or other software to perform fan control. Need for fan control As modern PCs grow more powerful so do their requirements for electrical power. Computers emit this electrical power as heat generated by all major components. Heat production varies with system load, where periods of compute-intensive activity generate much more heat than the idle time does. Processors in most early x86-based computers, up to some of the early 486s, did not need active ventilation. Power supplies needed forced cooling, and power supply fans also circulated cooling air through the rest of the PC with the ATX standard. The byproduct of increased heat generation is that the fan(s) need to move increasing amounts of air and thus need to be more powerful. Since they must move more air through the same area of space, fans will become more noisy. Fans installed in a PC case can produce noise levels of up to 70 dB. Since fan noise increases with the fifth power of the fan rotation speed, reducing revolutions per minute (RPM) by a small amount potentially means a large reduction in fan noise. This must be done cautiously, as excessive reduction in speed may cause components to overheat and be damaged. If done properly fan noise can be drastically reduced. Fan connectors The common cooling fans used in computers use standardized connectors with two to four pins. The first two pins are always used to deliver power to the fan motor, while the rest can be optional, depending on fan design and type: Ground common ground Vcc (Power) nominally a +12 V supply, though it may be variable depending on fan type and desired fan rotation speed Sense (or tachometer) output from fan outputs a signal that pulses twice for each revolution of the fan as a pulse train, with the signal frequency proportional to the fan speed Control input a pulse-width modulation (PWM) input signal, used when the cooling fan assembly has an internal motor driver circuit. Fan assemblies with this control input provide the ability to adjust the rotational