Edit.Benchmarking the Benefits of PCI-E 3.0
One of the points about the Southern Islands products that are bound to come up in countless marketing documents is their use of the new PCI-E 3.0 specification. Much like the switch between PCI-E 1.1 to 2.0, this certification incorporates several new features that could prove to be hugely beneficial to graphics card manufacturers. First and foremost among the improvements is a brand new encoding scheme that helps it effectively double the bandwidth of PCI-E 2.0 to 8 GT/s.
While current generation single and dual GPU cards still fit well within the bandwidth limitations of PCI-E 2.0 x16 slots, Tahiti's creators will be trumpeting PCI-E 3.0 to anyone within earshot. However, does it really make a difference in gaming scenarios? More importantly, will upgrading to a PCI-E 3.0 motherboard allow the HD 7970 to pull further ahead of the competition? To find out, we used an ASUS P9X79 motherboard (which allows users to switch between Gen 2 and Gen 3 PCI-E functionality in its BIOS) along with our usual stable of games and benchmarks. To ensure outside factors didn't play into the equation, the highest resolution and image quality settings were used in every game.
Starting things off was 3DMark 11 and the differences between a Gen2 and Gen3 interface was effectively nil. From the perspective of 3DMark, it really doesn't seem to care whether the HD 7970 runs on a higher bandwidth interface or not.
The results couldn't be any clearer: the HD 7970 doesn't benefit in any way from a PCI-E 3.0 link to the CPU. Granted, there were a few small increases (and decreases) here and there but these are a result of averaging out the results from multiple manual benchmark runs and fall well within our margin of error. So to the relief of gamers and reviewers alike (hey, we still love our X58 test systems!), a next generation PCI-E interface isn't needed to get the most out of the Tahiti XT core.
However there are a few caveats that should be mentioned. Even though a single HD 7970 may not saturate a PCI-E 2.0 x16 slot, things could change drastically once two of these cards are installed into a Z68 motherboard which uses a dual 8x setup for Crossfire and SLI. Things will likely get even more complicated when AMD's new dual GPU product is released in the first half of 2012. We'll likely revisit this topic throughout 2012 but for the time being, rest assured knowing that AMD's HD 7970 is in no way limited by current PCI-E certifications.