Multi-GPU Setups: The Basics Of CrossFire And SLI

AMD Or Nvidia?

AMD calls it CrossFire, Nvidia calls it Scalable Link Interface (SLI). In essence, both companies are using a similar concept to distribute the workload presented by your favorite game across two, three, or four graphics cards.

Installing a multiple graphics card setup can be a bit tricky, and there are several questions you need to answer. How fast must the PCI Express slots be (we'll have a story posted next week addressing this one in depth)? Do you need a bridge connector between the cards? How powerful should the CPU be to make proper use of this graphics muscle? We asked ourselves these questions, ran scaling tests, compiled the results, and came up with some great tips for you.

In order to evaluate how SLI and CrossFire scale with CPU performance, we increased the default 2.66 GHz clock rate (133 MHz x 20) of our Intel Core i5-750 reference processor to almost 4 GHz (190 MHz x21) by modifying the base clock and multiplier in the BIOS. On all Intel processors with Turbo Boost feature (that aren't Extreme Edition or K-series parts), you can only increase the multiplier by one increment. We used a Gigabyte P55A-UD7 motherboard and disabled Turbo Boost. The number of CPU cores remained unchanged.

Unlike many other platforms, which are limited to CrossFire, our our P55-based Gigabyte board supports both CrossFire and SLI, making it easier to keep the platform consistent.