Question
On many computers, when the computer is turned on (even before POST), the fan spins up to high speed momentarily, then settles down to normal operating speed. This appears to be normal, but why is this done, and what purpose does this serve?
Answer
Because the power is turned on to the fan, before the BIOS loads any real time controllers that will base the speed of the fan on the temperature of the processor. This also keeps the processor from getting excessively hot if you were to try the alternative… which would be to keep the fan off until those controllers were loaded and basing the fan speed on processor temp. More of a safeguard than anything. The processor is starting to work the moment you turn the computer on, but the BIOS still needs time to load.
Here is another alternative. What if the BIOS didn’t load for some reason… a stick of Ram gone bad, for example. Would you really want your processor sitting there with no fan, waiting for the BIOS to turn on the fan after it loaded the appropriate controllers? I know I wouldn’t.
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