X-bit labs

NVIDIA Multi-GPU SLI Technology: New Approach to Old Ideas (page 16)

Category: Video

by Alexey Stepin , Yaroslav Lyssenko, Anton Shilov

[ 02/25/2005 | 02:15 PM ]

Doom III

NVIDIA’s SLI did well in Doom 3, although its advantage is close to nothing in low resolutions: the scene recorded on the Hellhole level contains a battle with numerous monsters and the speed here mostly depends on the CPU characteristics rather than on the graphics subsystem. You can see the positive SLI effect in 1280x1024 where the GeForce 6600 GT duo performs like the single GeForce 6800 Ultra. The system with two GeForce 6800 Ultra showed its best in the highest resolution, but the performance gain was not twofold.

The efficiency of NVIDIA’s multi-GPU rendering grows up as we enable such eye-pleasing features as full-screen antialiasing and anisotropic filtering. The limiting influence of the CPU is felt less here, as the graphics subsystem bears a higher load. The GeForce 6600 GT couple evidently felt the lack of the graphics memory – the memory of the graphics cards in a SLI configuration has identical contents, i.e. its total amount remains the same (128 megabytes in this case) rather than doubles. We tested this game with the highest graphics quality settings, so the relatively low results of the GeForce 6600 GT SLI must be due to the low memory amount. The GeForce 6800 Ultra SLI looks better – the multi-GPU mode provides a performance boost up to 75 percent in high resolutions.

The d3dm4 scene is simpler: there are no monsters here, but the player is shooting from a plasma rifle or a rocket launcher from time to time. The SLI effect is noticeable even in the lowest resolution and is growing up to 60-65 percent in 1600x1200.

Again the lack of the memory affects the results of the GeForce 6600 GT SLI in the “eye candy” mode, so the SLI effect amounts to 60 percent in 1600x1200 only, while the pair of GeForce 6800 Ultra cards are 80-95 percent faster than the single card. We want to remind you that we tested the single GeForce 6800 Ultra on the VIA K8T800 Pro platform, so we should make allowances for the difference between the platforms when comparing the results.