SL Why? Scalable Link Interface Article

In the most basic sense, SLI works in one of three modes: Compatibility mode, Alternating Frame Rate (AFR), and Split Frame Rate (SFR). Since not every game is compatible with SLI, drivers have to be configured to instruct the cards how to run in certain applications. Some games, like Painkiller, Doom3, and FarCry, run in SFR mode, which means that the two video cards work independently and each renders half of the frame that is to be displayed. Afterwards the two halves are combined into a single image. In AFR each card works independently to render alternating frames which are then displayed continuously. This method is featured in games like Half Life 2. Compatibility mode- which seems to be a bit of misnomer- leaves only one card rendering and there is no added performance. This would be used for non-SLI compatible games like Flight Sim 2004 and Madden NFL 2005. (Using driver version v71.24)

SL Why? : A Short Discourse on Scalable Link Interface
XYZ Computing