Three-Way Goes Mainstream?
Captain Obvious dictates that, in order to properly support three graphics cards, your motherboard needs three PCIe x16 slots. Boards with three slots have been available at multiple price points for several generations. The problem with most of those boards was that the third slot was limited to only four PCIe 1.0 lanes. Nvidia would never allow such a low-bandwidth slot to support SLI because the card in the slowest slot often dragged down the performance of every other card in the array.
This is where enthusiasts might scream for a chipset with 48 PCI Express 2.0 lanes to support three graphics cards at full bandwidth from the primary controller. Unfortunately, no such product exists (though AMD comes close). Our own tests have shown that x8 mode is not much of a hindrance to SLI performance on Nvidia’s fastest cards, since CPU bottlenecks come into play long before a PCIe 2.0 x8 slot is completely tapped-out.
So, is the real requirement of three-way SLI really something as simple as a chipset that has 24 direct pathways? While many of our readers recommend X58-based motherboards to their friends specifically for the platform's 36 PCIe 2.0 pathways, we didn’t say that those lanes all had to come from a PCI Express controller. Long ago, Nvidia figured out that, since every card in an SLI array uses the same data, repeating data is an easy way to feed two graphics cards with the full 16 lanes of bandwidth from a chipset that supports only one x16 card. Nvidia calls this method “broadcast” and began using it several years ago to convert its low-cost 750a SLI chipset into a multi-card-supporting monster.
This bridge has since been used on everything from its 680i to Intel’s X58, opening three-way SLI to a broad customer base. Today we consider one such motherboard that allows buyers of mainstream LGA 1156 processor buyers to seek the ultimate level of features and graphics performance, and see how it compares to an LGA 1366 alternative.