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NVIDIA's SLI resurrects GPU teaming


Kickin' it old school—with 32 pipes
— 9:58 AM on June 28, 2004

AS I WAS PREPARING our review of the new PCI Express stuff, fellow TR staffer Andy Brown dropped in to Damage Labs for a look at the new hardware. I showed him the PCI Express version of the GeForce 6800 GT, and he noted a funny connector on the top of the card that looks like this:


The "golden fingers" connector on the PCI-E version of the GeForce 6800GT

"That's the SLI connector," he joked. I responded with what I thought was the proper sarcasm. I mean, us old timers like to recall the days of the ancient 3dfx Voodoo 2 graphics cards, when 3D graphics on a home computer was still a new experience, and Voodoo 2 SLI ruled the graphics world.

SLI stood for "scan line interleave," which was 3dfx's means of distributing the workload between a pair of PCI graphics cards in order to boost performance. Stick a couple of Voodoo 2 cards into your box, connect them together, and one would literally draw the even-numbered scan lines on the screen while the other drew the odd-numbered lines. Since the Voodoo 2 was the fastest graphics card available on the PC during that time, owning a pair of them made a person Head Geek on the block. They would rip through Quake II like nothing else.

But us old timers knew those days wouldn't return. Nowadays, we have $500 graphics cards with sixteen pipes each sucking more power and producing more heat than a Coleman electric grill. Plus, AGP slots are a singular experience in bus contention. Surely those funny golden fingers on the GeForce 6800GT were only an odd appendage on a rush, pre-production graphics card, nothing more.

Turns out I couldn't have been more wrong, and Andy couldn't have been more right.

SLI reborn
Today, NVIDIA is announcing is new SLI technology for GeForce 6800 graphics cards with PCI Express. Those "golden fingers" protruding from the top of the GeForce 6800GT are, in fact, an SLI connector. Place a pair of GeForce 6800GT (or pick your flavor, including GeForce 6800 Ultra) cards into a special motherboard with a pair of PCI Express X16 expansion slots, and this connector will help hook the two cards together for tandem operation. Like its predecessor, the new SLI will accelerate graphics and games on a single monitor using two graphics cards. For real.


NVIDIA's SLI link card. Source: NVIDIA.

Of course, NVIDIA bought up the remains of 3dfx when the end came. Why not resurrect the SLI acronym for this new dual-GPU config? This time around, SLI stands for Scalable Link Interface, since the cards will not be using scan-line interleaving to distribute the workload.


A pair of cards in an SLI config. Source: NVIDIA.

I should note at this point that NVIDIA's new SLI is distinct from the VideoArray dual graphics technology being touted by Alienware. That technology claims to be independent of the brand of graphics card used and will be proprietary to Alienware. NVIDIA built support for SLI right into the NV40 GPU, and will be offering SLI configurations to consumers through multiple partners.