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Micro-Stuttering And GPU Scaling In CrossFire And SLI

Step 2: CrossFire With Three GPUs

One Radeon HD 6870 X2 and One Radeon HD 6870 Give Us Three-Way CrossFire

Using PowerColor's Radeon HD 6870 X2 lets us bridge three Barts GPUs, despite only having a single bridge connector to tack on a Radeon HD 6870 card. Can three mid-ranged hearts beat in unison?

The total price of these test cards add up to about $650. That's still $80 less than a GeForce GTX 590 though. Unfortunately, all of AMD's Radeon HD 6990s have seemingly been deactivated from Newegg, Zipzoomfly, and TigerDirect, so there's really no valid comparison there.

But after looking at the graphs, the lack of 6990s is hardly what perplexes us.

We repeated this same test using a number of games yielding different average frame rates. So long as the average is above 30 FPS, the resulting output is almost stutter-free. Minor differences in when frames hit the screen are not apparent, and so they don't bother us at all. The experience is similar to using a single GPU.

After analyzing the dual-card configuration, this is certainly not what we were expecting.

Interim Assessment

Amazingly, the three-way setup has a tremendous advantage over two cards in CrossFire. Additionally, it costs less than the dual-GPU GeForce GTX 590 and Radeon HD 6990 cards, too. Of course, the average frame rate only really increased about 20% compared to a Radeon HD 6870 X2, and 420 W worth of power draw is no small figure. It'd take an overclocked Radeon HD 6990 to top that.