PWM-Z (Zero) fans stop spinning below 20 percent duty cycle. This allows OEMs and motherboard manufacturers to shut off the fan at low duty cycles rather than idling a pulse-width-modulated fan at low speed, thus eliminating fan noise and vibration. The fan will start spinning at a duty cycle of 30 percent; then, the fan can be slowed to an idle speed of 600 rpm at 20 percent duty cycle. If the duty cycle is reduced below 20 percent, the fan stops spinning.
July 1, 2005