Discussing your MB fan headers.
Discussing your MB fan headers.
The pins on the CPU_FAN header are distinct because they control different fan speed modes. The GND-12V sensor speed setting versus the general GND-speed control-sense-VCC configuration serve separate purposes. All fan headers can operate in PWM mode, allowing variable speed control. Regarding the fan speeds, connecting a PWM 4-pin fan to SYS_FAN enables PWM operation, while a 3-pin fan runs in voltage mode. Your understanding is correct. Concerning the maximum current, those values depend on your motherboard and fan models—please check your specific components for accurate limits.
It could be that the CPU fan header lacks DC fan control capabilities, whereas the others function properly. Having the board would help confirm this. Likely yes on that specific board. Generally, no—4-pin supports PWM, 3-pin only DC speed control. Most people refer to it as DC mode, but Gigabyte actually uses voltage mode. Unless specified otherwise, assume 1A capacity. Some headers are built for higher power (pump headers, 2A), but there’s no clear indication on the board.
The MSI board I'm examining features various labeling for cpufan and the remaining components...
It's true anything can happen, though I'm not sure. Typically the DC/PWM setting is chosen automatically by the board based on the fan model, so it's usually not something to fret about. However, the only functional Gigabyte board I have is an X570 Aorus Master, which doesn't list that feature in the manual, making it hard to verify my idea without checking firsthand.
Everything is clarified in this guide: FAQ – How do I verify if my 4-pin fan header supports PWM? Some motherboards include 4-pin headers that don’t actually use a PWM signal on Pin 4 for speed control. Instead, they adjust voltage at Pin 2, similar to a regular 3-pin header. Since the minimum speed usually exceeds the speed at 20% PWM duty cycle, the fan can’t achieve lower speeds under voltage control compared to PWM. Check your motherboard manual to confirm whether it uses 4-pin headers that manage speed via voltage reduction on Pin 2. Manufacturers often label Pin 4 differently—terms like “+5V”, “VCC”, or “NC”—but if these terms suggest PWM, the header likely doesn’t support it. If Pin 4 is labeled “Speed Control” or “PWM,” you’re safe to assume PWM support. Be aware that pin descriptions can be misleading; some models let you switch between voltage and PWM control in BIOS, even if the manual doesn’t mention it. If unsure, reach out to your motherboard maker. For compatibility, if your board has other 4-pin headers that use PWM, you can connect multiple fans using Y-splitters. Just remember not to surpass the fan’s rated power (typically 10-12W).