PCI express & SLI

PCI express is the result of intel labs' rework on the classic PCI bus, allowing data to be transfered at twice the speed of an 8x AGP video connector. Also, PCI express allows for multiple video cards to be used simultaneously. With NVIDIA, this is called "SLI" (Scalable Link Interface) and ATi's response is "Crossfire". Currently, SLI is only available on newer intel-based and NForceSLI-based chipsets. Crossfire is available on Radeon Xpress Chipsets. For SLI to work, you must have 2 indentical video cards, in identical PCI-e x16 slots. So, if you had for example a BFG 6800GT Overclock series, and wanted to run SLI, you'd need another BFG 6800GT Overclock series. ATi is a little more leniant. The brands can be different, and you could even use another core, as long as the card in PCIex16_1 slot (the first PCI-e slot) is "Crossfire enabled". For example, you could use a Radeon x850xtPE CE in PCI 1 and then have an x850, an x850 Pro, an x850xt,or an x850xtPE in slot 2. The major difference is that in SLI, one card renders the horizontal while the other renders vertical. in CF, one card renders a 'checkerboard' like pattern, and the second card fills in the blanks. For the most detailed specs, see http://www.tbreak.com/reviews/printpage.php?id=378