3dfx, rest its soul, gave us all something to lust after in its Voodoo2 SLI product. Standing for "Scan Line Interleave," SLI technology allowed you to connect two Voodoo2 cards together, and the two would pair on rendering games by each handling every other line on the display (e.g., card 1 would do the even lines, card 2 the odd). Such was geek lust in 1998. In 2004, tag-team rendering looks like it’s going to be all the rage again.
First, of course, there’s Alienware’s Video Array technology, but that’s proprietary and apparently only available in extremely expensive (although well-crafted) systems. NVIDIA wants to change all that. Owing to the advent of PCI Express, the conditions are ripe for multi-card solutions, and NVIDIA saw this opportunity earlier than most, building support for cooperative rendering into the NV40. Connecting two cards by means of a small bridge, NVIDIA’s technology splits the screen in half horizontally to divvy up the workload, but here’s the kicker: the division isn’t fixed. Rather, using load balancing techniques, NVIDIA’s solution assures that both cards are doing as much as they can. If you can imagine 3D games where part of the screen is mostly static (a HUD, a dashboard, your flight controls, etc.), you can see why this is a boon (Alienware’s solution is somewhat similar). So, meet NVIDIA’s Scalable Link Interface, aka, the new SLI.
What’s the price for entry? As you would expect, you’ll need two identical 6800 PCI Express cards and a motherboard that sports two X16 slots. Currently you can’t pick up a consumer-class motherboard that fits the bill, and few people are insane enough to opt for a dual-Xeon solution to get dual X16 support (aside: iWill’s board for Alienware uses one X16 and one X8 slot). Not to worry, however. NVIDIA’s future PCI Express nForce chipsets will more than likely support two X16 slots, and other chipset makers, including Intel, may follow suit. Still, the lack of production motherboards supporting this means that it will be a while before you can get your hands on a proper SLI solution. Indeed, no one has been able to benchmark this aside from NVIDIA, who claims to see a 87 to 100% increase over single card solutions in 3DMark03 and Unreal Engine 3 (respectively). We’ll see about that.
NVIDIA will begin by offering specialized systems through the OEM channel, with attention to the DIY market following thereafter. As for ATI, will they hop on board, too? It’s hard to say. Even if SLI is out of the price range of many gamers, the concept will likely influence buying decisions. The allure of picking up a certain US$300 video card today is much more attractive if you know you can pick up another one for e.g., $200 in a year’s time, and nearly double your performance. SLI might not get used that often, but it will sell cards. More in-depth information (plus a lot of superfluous information) can be found at Tom’s.