New Computer Fans rev up

[Panda25]

I was wondering, do all new computers rev up really fast when they first boot up?  When I press the power button I believe it's the power supply fan or some other fan that really revs up for about 5-10 seconds and then goes to a slower speed.  I've set up some new computers at work too and they rev up for 5-10 seconds and then slow down again.  What is the purpose of this?  Is there a way to stop it from doing this or is this just how new computers are set up?  (By new I mean 1 year old or less.)

[Deerpark]

I wouldn't be able to say if all newer computers do this, but yes I've noticed this too. My theory is that when you power up the computer the fan is getting full power, and therefore runs at max speed. Then the BIOS takes over and regulates it down to a more suitable level. The reason it is so noticeable on newer computers is because fans don't run at as many RPMs as they did a few years back.
But this is just my theory... take it or leave it.