I think they share data per frame like the original 3Dfx SLI (SLI = Scan Line Interleave). I'm not certain though. I'm not sure about how it handles asymmetry, but right now it's an nVidia-only feature, most likely inherited from 3Dfx directly, since they bought 3Dfx :) In other words, I don't know the answer to the second question. Hopefully we'll find out more soon, as the nForce4 SLI boards start shipping. Which reminds me -- there are actually 3 flavors of nForce4; one low(er) cost model, an upscale single PCIe slot model, and an SLI model, so not all nForce4 boards will be expensive.