CrossFire and SLI Dongle-less / Bridgeless Performance Analysis

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How much impact is there to SLI and CrossFire performance when the cards communicate over PCIe rather than dedicated links? We have some fun with high-end dongle-less and bridgeless multi-GPU rendering in an effort to find out. Our discoveries are quite interesting. Let think up a few drawbacks you might have on your mind. There's price, drivers, game compatibility, platform issues, power requirements, the setup and more. Oh, what a minefield... except it's not quite that bad and it's continually getting better.

We could wax lyrical about how yes, some single cards cost and perform the same as two cards in dual-GPU mode, but that with two cards there's the upgrade path of buying one now and another later... or we could talk about how game support is constantly being tweaked with every driver release. In fact, we could rattle on for hours about it, especially with assistance of a Hoegaarden or two.

We'll spare you the trauma, however, and focus on just one aspect of multi-GPU rendering that could be seen as an annoyance: bridges and dongles. With all that bandwidth on PCI-Express-enabled motherboards, how is it we still need to provide a link between our two graphics cards before they'll work harmoniously? Be it internal SLI bridge or external CrossFire dongle, sometimes it can prove problematic, especially for the downright lazy.

Bridgeless and dongle-less multi-GPU rendering isn't exactly new. We've seen it on lower-end SLI and CrossFire solutions, but now it's starting to rear its head higher up the product ranges, where the lack of a dedicated inter-card link might have a bigger impact. Shall we see if it does? OK then!

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