In order to use SLI, a motherboard with an nForce4, nForce 500, nForce 600 or nForce 700 SLI chipset must be used. Although with the use of hacks and older drivers, one can make SLI work on motherboards with Intel, ATI and ULi chipsets, Nvidia has stated that only their own chipsets can allow SLI to function optimally, and that they will not allow SLI to work on any other vendor's chipsets. Some early SLI systems used Intel's E7525 Xeon chipset, which caused problems when Nvidia started locking out other vendor's chipsets as it limited them to an outdated driver set. In 2007, Intel has licensed Nvidia's SLI technology for its SkullTrail platform, and select motherboards supporting the Intel X58 (Tylersburg) chipset have unlocked SLI capabilities. Not all X58 motherboards support this technology, as Nvidia offered it to motherboard manufacturers at the cost of $5 per motherboard sold.[18] 
clipped from: en.wikipedia.org