"Currently, SLI allows you to accelerate rendering using two effective modes, which map to around four general cases of multi-GPU rendering. The first, SFR or split-frame rendering, has each graphics card render a portion of the screen, split horizontally. One card, the primary device on the PEG host, is responsible for the top section of the screen, the secondary device therefore responsible for the bottom. That situation is then load balanced. More on that shortly.

The second mode is AFR, or alternate-frame rendering. For each graphics device in the system, the driver round-robins the graphics commands and data to each device, forcing each device to render a frame in turn. For a dual-GPU SLI setup, each device renders a frame, waits for a frame, then renders a frame, ad infinitum. Interleaved with the second device doing the same, that's AFR in a nutshell."