SLI is no joke
The setup Metabyte had for us was demonstrating proof of concept, or in less pretentious talk, "this thing is real and it exists now." The setup was a Pentium II 400 with two modified 3DFX Banshee cards, pimpin' the Stepsister technology. Before we got on with the demo, we had a few questions about the technology that our hosts were more than happy to answer.
First, the term "SLI" is technically a misnomer. "Scan Line Interleave," is the technology used for 3DFX's current Voodoo2 3D-only chipset. With true SLI, one card renders all of the even horizontal scan lines, while the second card draws all of the odd scan lines. As you can imagine, this leads to an even load distribution between the two cards, and theoretically doubles the fill rate and triangle rate.
However, before everyone goes around half-cocked about double the performance, remember that any kind of "SLI" will share many of the characteristics of a standard Voodoo 2 setup. You'll definitely see a big jump in performance, but depending on where your bottlenecks are, you may or may not see close to two times the performance.
Right. However, you can't really ignore the power behind the "SLI" name - among gamers, it's universally accepted as "a method to increase performance by combining two 3D cards in one system." What the boys at Metabyte did is split the load from top to bottom - one card renders only the top half of the screen, another handles the bottom half.
Another pretty obvious point is that the technology isn't officially named "Stepsister." It's just a joke phrase that came about since the Voodoo2 was a "daughtercard" (another of your misnomers actually), so using real 2d/3d cards would be "sister cards." However, since they were never supposed to be used together, they're "stepsisters." Get it? Internally, Metabyte uses the phrase "Parallel Graphics Processing," but the official name of the project will probably change.
What really got me jazzed was the fact that you can use PGP with a combination of AGP and PCI cards, something 3DFX once said wasn't possible unless systems started shipping with 2 AGP slots. One of the things that's always just nagged at me was the necessity to have three video cards in my system for SLI! As if two wasn't enough!