One card draws the top half of the screen, one card draws just the bottom, a little chip going across the top synchs them up, and there's SLI. Even if it's performing at half the bandwidth, you got double the GPU power, basically SLI is power hungry and wants the highest settings you can give it, that's where you notice the biggest gains from SLI, not from wanting sli and putting stuff on low settings. IMO they need to come up with a better more efficient card. The 6800 is a damn fine card and they jumped a good leap in graphics, but now they are having to simply use two cards in one system? That's gotta create monsterous heat and a hefty price tag