"DC Fan" fan speed can be when you start the computer through the BIOS test, or by other onboard monitoring software testing; can also speed tester. Note: The first two methods must be supported by the fan speed function can be measured. There are two methods for measuring air flow and pressure, one instrument with wind tunnel testing, the other is a double box measured. But for the average user, there is no such device. Only as a reference, ultimately depends on the cooling effect according to the data provided by the manufacturer.