What will happen if I plug a 3-pin fan into my CPU-fan header, which is 4-pin?
Will the 3-pin run full speed?
PWM question
Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee
By default, a 3-pin fan plugged into a 4-pin header will always run full speed at 12V.
On budget motherboards, that's it. More expensive boards often include voltage control circuits that can control 3-pin fans. For example, high-end ASUS and Gigabyte boards have several headers that can control 3-pin fans.
The way to tell is to either RTFM (!!!), or go into the BIOS hardware monitor screen and see if you're offered the option of changing the speed control for the header you're using (almost certainly the CPU fan header, since it's still extremely rare to see 4-pin headers elsewhere). On ASUS boards, this option is called DC/PWM even though both are really PWM; it would more accurately be called 4-pin/3-pin mode.
On budget motherboards, that's it. More expensive boards often include voltage control circuits that can control 3-pin fans. For example, high-end ASUS and Gigabyte boards have several headers that can control 3-pin fans.
The way to tell is to either RTFM (!!!), or go into the BIOS hardware monitor screen and see if you're offered the option of changing the speed control for the header you're using (almost certainly the CPU fan header, since it's still extremely rare to see 4-pin headers elsewhere). On ASUS boards, this option is called DC/PWM even though both are really PWM; it would more accurately be called 4-pin/3-pin mode.