HD3870 Crossfire Scaling: P35 vs X38

Overall Score

Elder Scrolls IV: Oblivion

When Bethesda Softworks released the fourth installment in their Elder Scrolls Series, Oblivion, back in 2006 it proceeded to stress any and all graphics cards which attempted to render it. Modern cards such as the HD38x0 and GeForce 8800 can now run Oblivion with all options on and reasonable framerates, but the game is still graphically challenging. Oblivion was tested with a manual walk through the forest with heavy vegetation ending at an Oblivion gate, and performance was captured using Fraps. First up we see the results running the X38 board with all in-game settings maximized and HDR activated, but no AA or AF in use.

Crossfire shows pretty good scaling on the X38 board in Oblivion, particularly as the resolution increases and the graphics processors are working harder and are less limited by other factors such as the CPU and the PCI express bus. Next we look at Oblivion on the P35 board.

The Crossfire scaling on the P35 board, while at least not detrimental as in CoD4, is nowhere near as good as on the X38 board until we get to 1680×1050 resolution. To see if the P35’s deficit would close further as the GPUs became more heavily worked, 4x AA and 16x AF were forced on using Catalyst Control Center and the tests were repeated.

With AA and AF on (mainly due to AA) the framerates dropped quite a bit on the X38 board, and the Crossfire scaling remained quite good. Even at 1680×1050, the framerate averaged over 60 FPS and never got below 40. Next up the P35 board was tested with AA and AF as well:

Here for the first time we see a case where the P35 board almost matched the Crossfire performance of the X38 board at 1680×1050 resolution – giving up an inconsequential 0.4 FPS and actually achieving a higher minimum rate during the test (although the minimum and maximum framerates showed much more variability from run to run than the average did so this should be interpreted accordingly). From this test it appears that as the GPUs themselves become highly stressed the bandwidth of the PCIe link becomes much less important.

The charts below summarize the scaling performance under Oblivion for both boards. The single card framerate was averaged and combined into a single data point since the single card performance of the cards was similar enough.

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