Arctic Cooling's Freezer 32 CPU cooler promises silence at idle
 

We've enjoyed the recent explosion of semi-passive graphics card coolers that stop their fans while the GPU is idle. Arctic Cooling is extending that idea to the CPU cooler with its Freezer 32 series of heatsinks. The company is a little cagey about how its semi-passive system works, but it appears that a controller built into the Freezer 32's 120-mm fan can shut off the spinner entirely when the PWM signal from the motherboard falls below a certain duty cycle threshold. Arctic says most boards can't deliver PWM duty cycle signals below 40%, so we imagine that's the magic number. As a result, no external hardware or cabling is needed: the fan plugs right into the CPU fan header, just like it would with any other heatsink.

http://techreport.com/news/29096/arc...ilence-at-idle