Is high-frequency PWM a feature of the motherboard?

[floepie]

From what I've been reading, low-frequency PWM can be used with 3-pin fans, and it is the way most motherboards/BIOS's vary fan speed, as opposed to varying the voltage in a linear fashion. This has the desirable effect of a greater control range of fan speed. The downside of low-frequency PWM often results in an audible clicking noise, especially with long "off" periods (slow speeds).

A 4-pin fan can take advantage of a high-frequency PWM, where tach readings are more accurate due to the fact that power to the fan is never actually cut off. High-frequency PWM can also quiet the audible side effects of very low-frequency PWM.

My question is, does the presence of a 4-pin fan header on the motherboard indicate that high-frequency PWM can in fact be used? Or, does the 4th pin/lead on some headers simply allow the system to gain more accurate tach readings, while other headers may have the full high frequency PWM function?

[Cerb]

Yes, it indicates that the higher frequency control can be used. You must plug a 4-pin fan in to get that, though, and you still may not be able to get really good control over it (depends on the board).

[cpemma]

My question is, does the presence of a 4-pin fan header on the motherboard indicate that high-frequency PWM can in fact be used?

There seems to be confusion regarding some boards. The Intel ICH9 Southbridge can control 3 PWM fans but boards rarely implement the full number.

The ICH9 integrates four fan speed sensors (four TACH signals) and 3 fan speed controllers (three Pulse Width Modulator signals), which enables monitoring and controlling up to four fans on the system.

My Gigabyte P35-DS3L board has two 4-pin headers; the manual only claims to speed-control the CPU fan header based on CPU temperature. Similarly on the newer GA-X48-DQ6 with ICH9R SB,

1. System voltage detection
2. CPU/System temperature detection
3. CPU/System/Power fan speed detection
4. CPU overheating warning
5. CPU/System/Power fan fail warning
6. CPU fan speed control

No mention of anything other than the CPU fan. It's as well to read the board specification, manual, and user comments if it's important to you.