Asus M4A79XTD EVO/USB3 - Manual (Page 80)

3-24 Chapter 3: BIOS setup
Chapter 3
Chassis Q-Fan Function [Disabled]
[Disabled] Disables the Chassis Q-Fan control feature.
[Enabled] Enables the Chassis Q-Fan control feature.
The following item appears only when you set Chassis Q-Fan Function to [Enabled].
Chassis Q-Fan Mode [Silent]
[Performance] Sets to [Performance] to achieve maximum chassis fan speed.
[Optimal] Sets to [Optimal] to make the chassis fan automatically adjust
depending on the chassis temperature.
[Silent] Sets to [Silent] to minimize fan speed for quiet chassis fan operation.