"24V DC Cooling Fan" Speed is the number of revolutions per minute of the fan blades, the unit is rpm. Fan speed is determined by the motor inside the coil turns, operating voltage, the number of fan blades, tilt, height, diameter and bearing systems. Fan speed and quality are not necessarily linked. "24V DC Cooling Fan" can be carried out by the speed of the internal speed signal measurement can also be measured by an external (external measure is to see how fast the fan speed with other instruments, internal measurements directly to the BIOS can see, you can also look through the software "24V DC Cooling Fan". internal measurement error is relatively larger).