CPU Scaling: AMD
The plot thickens as we swap from Intel-based X58 and P55 platforms to an AMD-based 890FX-equipped machine. We're again starting with a fast hexa-core processor and turning off one core at a time in order to figure out how well-threaded Cataclysm might be.
Notice that the CPU's model number is obscured. We used the fastest chip we could get our hands on; unfortunately, it isn't available yet (though it will be soon).
Whereas the overclocked six-core Intel chip hits its stride with just two cores enabled, AMD's Phenom II flagship doesn't realize its upper bound until three cores are turned on. The line chart fills in our blanks. With all six cores enabled, the Phenom II X6 hits much higher maximum frame rates, pulling the average up substantially.
If you run the game in Windowed mode and open up Windows Task Manager next to it, the cause becomes clear. WoW pegs a single Phenom II core at 100% utilization. It also pegs two cores at 100% utilization, hence the step up in performance. It's only when you have three cores available that the game has a little headroom to spare. That wasn't the case with Intel's Core i7-980X, which handles the game deftly using fewer resources.
So what happens when you drop some of AMD's less expensive processors into the Socket AM3 interface?
Because we're already working with significantly lower average frame rates (compared to the Intel processors), we don't need to test as many CPUs here. Overclocked to 3.7 GHz, our mystery Phenom II X6 isn't able to add any additional performance, suggesting that clock rate isn't our bottleneck here. In fact, it's the lack of cores and cache that seems to hurt the two Athlon II chips most.
Although every single benchmark result on this page is generated with the help of a GeForce GTX 480, frame rates drop under 40 FPS on the Athlon II X2 system. There's simply not enough processing horsepower in the Athlon II or Phenom II lineups to let our graphics card stretch its legs.
Could it be a problem with Nvidia's GPU? We dropped a Radeon HD 5870 in with our Phenom II flagship to check and came up with 59.19 FPS in the same test (a mere 1.31 FPS difference). Clearly, AMD's CPUs are holding back performance in Cataclysm compared to Intel's processors.