Editing Computer fan control (section)

== Hardware ==
Most modern motherboards feature [[hardware monitoring]] chips, which are capable of performing fan control,<ref name=ieee07>{{Cite conference
|author= Constantine A. Murenin |date= 2007-04-17
|url= http://sensors.cnst.su/IEEE_ICNSC_2007
|section= 1. Background
|title= Generalised Interfacing with Microprocessor System Hardware Monitors
|conference= Proceedings of 2007 IEEE International Conference on Networking, Sensing and Control, 15–17 April 2007.
|location= London, United Kingdom
|publisher=[[Institute of Electrical and Electronics Engineers|IEEE]]
|pages= 901–906 |doi= 10.1109/ICNSC.2007.372901 |isbn= 978-1-4244-1076-7
|id= IEEE ICNSC 2007, pp. 901–906.
}}</ref> usually through the [[Pulse-width modulation|PWM]] method as described above. These chips can be configured through [[BIOS]],{{r|sensors-mmath|p=§11.1|q=11.1.   Interfacing from the BIOS}} or by using specialised software once the operating system has booted.

Processors produce varying levels of heat depending on system load, thus it makes sense to reduce the speed of the fans during [[Idle (CPU)|idle]] to decrease the noise produced by fans running full speed, until the load does goes up, at which point fan speed must be adjusted promptly to avoid overheating. Modern hardware monitor chips, once configured, are capable of independently running this monitoring loop without any need for a functioning [[BIOS]] or an operating system.  This automatic control offered by some chips may be called Thermal Cruise mode for maintaining a thermal envelope, as well as Fan Speed Cruise mode for maintaining a specific fan speed automatically.{{r|sensors-mmath|p=§12|q=12.   Hardware Monitoring Chips}}

However, not all software is capable of accessing these advanced configuration parameters provided by some chips, and it is very common that the generic software implements only the most basic [[interface (computing)|interfacing]] with the chips, namely, an explicit setting for the duty cycle for each fan control setting, subsequently performing the duty cycle adjustments itself in software, and thus requiring that both the operating system, as well as this third-party software itself to continue running on the main CPU to perform the monitoring loop.{{r|sensors-mmath|p=§11.3|q=11.3.   SpeedFan on Windows}}  This may not be a problem until the system or the utility crashes, at which point the system may overheat due to the failure of the fans to maintain adequate cooling whilst running at reduced voltage and speed.