As you might know some processor power-saving technologies both from Intel and AMD from mobiles (laptops) have reached desktops quite a while already. Idea is pretty simple - OS have control over processor speed and voltage depend on processor load. Modern processors are more than powerful enough to do most of your tasks with same speed on lower clocks. Tasks as browsign internet, downloading/uploading, listening music, watching movies use online chats, work with office programs, file/web servers, other kind of servers (depend on their load) and many, many more. As example OS will keep processor clock much lower than nominal ones untill a specific level of processor load is achieved (like 30-40% usage with lowered locks) then OS will restore original speeds untill again load goes lower than specific level and lower the clocks again. This clock switching is done fast so you wont make a difference. Lower speeds for the processor can be achieved with lower processor voltage so voltage goes up and down automatically too. Frequency switching is done by changing processor multiplier as you will notice bellow. Intel call their power-saving technology SpeedStep and AMD - Cool'n'Quiet. As you see above they make big sense for laptops but maybe you wonder why is this useful for desktop computers. No you wont really save money from the lower power consumption 
except you use your PC for something as 24/7. Point is lower frequency -> lower voltage -> less heat -> lower temperature -> lower cooler/s RPMS -> less noise.
Now out of the theory - here some stuff that i could make concidering the setup (yes its not for all AMD/Intell systems but only for AMD). Here is the nominal values with Cool'n'Quiet dissabled:
Important nominal values here are:
- Voltage = 1.408V
- Core Speed = 1800 MHz
- Multiplier = x9.0
- HTT (Hyper Transport Technology - have the role of FSB or with other words - processor high-speed bus communication) = 201 MHz
Usually processor temp in idle vary between 32-34C depend on room temperature while the massive cooper cooler with turbine fin run on ~2700-2800rpm (it might look as low speed but it make alot of noise too!)
To enable Cool'n'Quite you need three things (third is optional):
1) download and install proper processor driver depending on the model and OS from [url=http://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_871_9706,00.html]here[/url]
2) and switch to Minimal Power Management
3) if you have changed processor voltage or multiplier in motherboard BIOS make sure you set them back to default so system then will be able to change them on its own
It would be best to check your BIOS for any options that allow dynamic processor cooler rpm's management depend on processor temperature. Some motherboards allow you even to set custom levels with temperatures and choosen by you cooler rpm's for that level. When you ready it will look like that:
Notice that processor voltage, core speed and multiplier have been automatically lowered in idle or untill processor load reach ~35%. Processor temperature is now down to ~29-31C and same time cooler is much quietter cause now it run at 1900-2000rpm's by my custom settings in BIOS and it will automatically vary when temperature change cause of the load.
*** And hey! Dont say anythign about my desktop, i know what you will say 
