I have desktop PC with Win7. In BIOS I've reduced CPU fan speed and it seems to work fine in all applications. However if I start something in fullscreen, the fans speeds up immediately and becomes really noisy. I'm pretty sure that CPU couldn't get hot in such a short period, so I suppose it's a software problem.

The question - is this a BIOS problem, or some Windows configuration or drivers? Any ideas appreciated!

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    If the fans are running faster in fullscreen mode then its required to cool the system. – Ramhound Mar 9 '15 at 14:26
  • The effect on fan speed may be worse if the CPU heat sink is dirty of heat sink compound is getting old. You might use a temp. monitor like hwmonitor_1.26 to confirm a big increase in temperature. – user3169 Mar 9 '15 at 19:00
  • The temperture is at 50-55C. I think it's ok. I have Core i7 960. It's critical temperture declared as 67.9 °C – Ilya Ivanov Mar 11 '15 at 15:43

You didn't specify what your hardware is, but some pc's have an onboard graphics that shares some hardware resources with the motherboard - such as main memory. If you have stacked up a lot of processes in memory, than going in full screen mode can tax the available memory, causing swapping and other inefficiencies that can lead to a cpu running close to 100% and thus requiring the fan to run. Things to try: use the performance tab on the task manager to check memory and cpu use.

Is the program that is going full screen a graphics intense program like a game? That would cause more computation to fill the expanded area. A dedicated graphics card can offload much of these tasks.

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  • Thanks for the answer. I'm using a PCI-E Nvidia card. So it's not related to integrated graphics. Speedfan says that the temperture is ~50C which I think is ok? – Ilya Ivanov Mar 10 '15 at 21:32

The fan controller knows when to speed us to keep the temp at 55. The fan will start to spin to prevent it from climbing. It doesn't kick in at the critical temp because it wouldn't be able to cool it down quick enough. the fact your temp is staying around 50 means the fan is doing what it should be doing. Go buy a silent fan. You shouldn't be lowering fan speed to reduce noise unless you have 10 fans. I run all my fans at full go and if I don't want to I turn them down by a fan controller. I would never try to tell my CPU fan to go slower though. That's just asking for issues. Get ear plugs or silent fans. I also put on ambient sounds like rain to prevent the fans from being so noticeable.

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