3-Way SLI: first tests

Author: Anton Rachko

Talks on the possibility to merge three video cards within a single system have long been around. It was originally assumed that the third video card would process the physics in games, but both NVIDIA and AMD preferred to engage it for processing graphics. After some calm period, the talks resumed again owing to the photos of a special 'triple' SLI-bridge which leaked into the press, and the recently presented AMD CrossFire X technology which allows merging three or four Radeon video cards within a single system. After a short calm, NVIDIA presented the 3-Way SLI technology for merging three video cards within a system. However, the motives that made NVIDIA and AMD start development of similar technologies are different. For AMD, it is the only way to compete against the NVIDIA "monsters", and for NVIDIA that was just another chance to prove its leadership and satisfy the needs of most demanding customers who find the price as the decisive factor. By now, the possibility to merge the "triple" SLI is supported by GeForce 8800GTX and GeForce 8800 Ultra which have two MIO connectors each. There is still no information on the possibility to merge video cards having one MIO connector, but it's quite possible that NVIDIA will not skirt them as well. It is assumed that 3-Way SLI will operate on motherboards based on both NVIDIA nForce 780i and those based on nForce 680i chipsets. Today's tests have become possible due to the help of Meijin company.

We were provided with a new computer of the Meijin Extreme series based on CPU Intel Q6850 and the BFG motherboard based on the nForce 680i chipset. The memory (RAM) capacity in the computer was 2 GB. For details, look at the below screenshots:

The computer used three GeForce 8800 Ultra video cards linked with a "triple" SLI-bridge.

The exterior side of the bridge is spacious enough, which made it possible to place a large NVIDIA logo on it.

The interior side of the bridge looks out of the ordinary because the number of connectors has been increased from 2 to 6. The rigid structure of the bridge strictly standardizes the distance among the video cards and in our case it equals to one expansion slot. We were able to estimate the capabilities of the 3-way SLI technology using 3DMark 06 and the games Call of Duty 4 and Crysis. Since the three video cards GeForce 8800 Ultra offer a really high speed, we ran the tests at 1680x1050 (approximately analogous to 1600x1200 for the 4:3 monitor) and 2560x1600 which is maximum possible for the Samsung 305T monitor that took part in the tests. For the video cards, we used ForceWare 169.15 beta specially written for operation with 3-way SLI. And it proved a surprise, by the way.

The line with anti-aliasing settings in the control panel turned out to be disabled. Unfortunately, RivaTuner was also useless, so we were restricted by the settings of the test applications. Let's start the tests!

3DMark 06 let us set 8x FSAA with the quality rate set to 2x. For comparison we also tested in the default mode and in the mode with the 3-way SLI technology (single video card) disabled.

The test results produced in the default mode do not demonstrate the power of the 3-card combination and even can scare potential buyers away from purchasing the bundle. On the other hand, in the demanding mode we see a more than two-fold speed gain when using three video cards. This suggests that the 3-way SLI is most useful in demanding modes. Now we move on to the tests run in the game Call of Duty 4 which were performed with the maximum 4x FSAA and 16x AF.

Again we can see the maximum advantage of the 3-way SLI technology in demanding modes. In the mode using the 2560x1600 resolution, the speed gain achieved from using three video cards amounted to 122%, whereas in the mode with the resolution 1680x1050 the gain amounted to merely 54%.

We ran the tests in the game Crysis in the DX10 mode with 16x FSAA and 16x AF.

Unfortunately, we were unable to run tests in the mode with the resolution 2560x1600 because of the lack of memory (RAM) capacity for this game. But despite that advantage of using the 3-way SLI is evident. In the mode using the 1680x1050 resolution, the speed gain achieved 131%! Note that due to the so remarkable speed gain the FPS approached closely to 40-50, instead of 16 on the single video card.

Final Words

Today's tests have proved to be interesting from both the practical and theoretical viewpoints. It was really interesting to have a hands-on experience of feeling the combination of three most powerful video cards by NVIDIA, and in theoretically, based on the test results in the most demanding modes, it becomes evident that the company is investing a lot into the quality of its drivers. The 3-way SLI technology is unlikely to become widely popular because of its high price and is more like a show-off, however, the leadership of NVIDIA is evident, and this fact should attract buyers to its side.