Any NVidia card back to the 6600 (Plain ol' 6600) will work in SLi. And crossfire limits you to either the X850, X1800XL, X1800XT. In ATi's defense, they were hit with the news of SLi very swiftly and had to design Crossfire from the ground up, whereas NVidia acquired the technology from 3DFX 6 years ago when they bought them.

SLi was around years ago, I believe the first mag I read with cards in SLi was in 1998, but it flopped, there was no market back then, since most onboard cards could play most games.

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