Gigabyte GA-M68M-S2 User Manual page 49

CPU Smart FAN Mode
Specifies how to control CPU fan speed. This item is configurable only if CPU Smart FAN
Control is set to Enabled.
Auto Lets BIOS autodetect the type of CPU fan installed and sets the optimal CPU
fan control mode. (Default)
Voltage Sets Voltage mode for a 3-pin CPU fan.
PWM Sets PWM mode for a 4-pin CPU fan.
- 49 - BIOS Setup