But it's a DIFFERENT SLI! it works in a completely different way.
For 3dfx, SLI was "Scan-Line Interleave". The way it worked is that each card rendered at half-height and the two pictures were mixed together, using alternate lines.
Split Frame Rendering, Alternate Frame Rendering, and SLI Antialiasing.
So card 1 renders the top half, card 2 renders the bottom half.
So GPU 1 is rendering frame 1, and at the same time GPU 2 is rendering frame 2.
Then it starts showing frame 1 (then 2) while frames 3 and 4 are being rendered
Instead of splitting up rendering, it's double-rendered but with different anti-aliasing patterns, then merged in the final step.
the 3dfx cards needed that little bridge connector to combine the two cards.
For Nvidia SLI & CrossFireX, bridge connectors help, but aren't required in all cases.
Higher-end configurations still benefit from the bridge connector, though.
The example given on wikipedia is that you can use a Radeon 5830 with a Radeon 5870
If you have a fast card and a slow card, they share 60/40 or 70/30 or whatever is needed to maximize performance.