The Tech Report has information about the new fan speed controller features of AMD's SB800 southbridge, head over to their site for the full details.
The SB800 family of south-bridge silicon has an integrated microcontroller that, with a little help from firmware built into a system's BIOS, can offer more control over that system's fans than has ever graced a motherboard. The microcontroller can manage fan speeds using three algorithms: step, linear, and non-linear. In step mode, fan speeds jump from one value to the next as temperatures rise. The linear algorithm smooths things out, allowing fan speeds to ramp, well, linearly between predefined minimum and maximum values. Combine the two, and you have a non-linear approach that's really more multi-linear. This method drapes a string of linear slopes across multiple step points.