"The rear portion of the Scythe Stealth Semi-Fanless Power Supply has all the standard features found on most PSU units but incorporates a large black coloured aluminum heatsink for passive cooling and an 8-position rheostat knob which controls Scythe's Flexible Fan Control System (FFCS). The FFCS is a unique system that provides six different temperature configuration modes as well as the ability to adjust fan RPM levels."