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PCIe Scaling Analysis

PCI Express And CrossFire Scaling: Is P55 Good Enough?
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In a perfect world, the P55 and X58 platforms would have identical performance with a single graphics card in x16 mode. The P55 Express does have the theoretical performance boost of an on-die PCIe controller, though a previous examination has shown that this advantage will likely remain only a theory for quite a while. A statistic that more than eliminates the small x16-mode difference we’ve measured is that, relative to competing products, the X58 motherboard performed slightly worse in its earlier review than the P55 motherboard did in its review.

Taking board-specific performance differences into consideration, the only noteworthy changes are a minor performance loss of around 4% when moving from PCIe 2.0 x16 to x8 transfers, a moderate loss of around 11% when moving from x16 to x4 mode using the X58’s four “left-over” PCIe 2.0 lanes, and a huge 30% performance loss when using four 2.5 GT/s lanes from the P55 Express PCH.

A difference of 4% might not make or break your gaming experience, but it can be huge in a performance shootout, such as our recent System Builder Marathon (SBM). Yet, there is one more variable to add, since those machines used CrossFire technology. Curious to find out how this 4% difference could affect multi-card systems, we began testing dual-GPU and triple-GPU CrossFire/CrossFireX configurations.

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