Despite Nvidia's claim that Skulltrail doesn't support 3-way SLI due to a hardware limitation, sources close to Intel have confirmed that this is purely a software issue. The hardware is capable of supporting it, but Nvidia’s driver is to blame for lack of support.
Once Nvidia makes a driver that works on Skulltrail, Intel will be able to showcase 3-way SLI; but Nvidia plays its own games and doesn’t want to give Intel 3-way SLI for now.
With the current driver, only normal SLI works and Quad SLI might only work with the old 7950 GX2 cards instead of the new 8800-series.
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PC Hardware
Skulltrail could support 3-way SLI, but

DistreeXXL: Nvidia doesn’t have a driver