There has been some discussion in the community that NVIDIA SLI is capable of running on Intel's i5000XL Greencreek Chipset, and that ATI CrossFire could even run on the Intel Chipset with its dual PCI Express x16 slots. The Greencreek is designed to be a premiere workstation Chipset for use with Intel Xeon Dempsey and Woodcrest processors. However, using the Tyan Tempest i5000XL, we threw in dual PCI Express x16 NVIDIA GeForce graphics cards to see if Scalable Link Interface was really possible. Using nvidia-xconfig --sli=AFR, the SLI option was added to the xorg.conf, however, upon rebooting we were unsuccessful in our attempts of using SLI. The NVIDIA x86_64 1.0-8762 Linux display drivers were unable to enable SLI on the Greencreek. Though the next NVIDIA Linux driver release (1.0-9XXX) may bridge support for this Chipset, at this time we were unsuccessful in our attempts. If we learn any additional information on this matter, we will be sure to pass it along. Below is the error from the X.Org log.
(**) NVIDIA(0): Option "SLI" "AFR"
(**) NVIDIA(0): Enabling RENDER acceleration
(**) NVIDIA(0): NVIDIA SLI enabled; using alternate frame rendering.
(WW) NVIDIA(0): Failed to initialize SLI! Reason: Unknown error. Only one
(WW) NVIDIA(0): GPU will be used for this X screen. Please see the SLI
(WW) NVIDIA(0): Appendix in the README for troubleshooting suggestions