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The Game Rundown: Finding CPU/GPU Bottlenecks, Part 1

Alien Vs. Predator

The test results yield two charts: the first shows the utilization of the hardware (CPU and GPU) in percentages and the second focuses on graphics performance using different core counts.

The results are not sorted, but the order remains the same throughout the article. In the first chart,we always list the Core i5 CPU employing one core first (black bar) followed by the GeForce GTX 460 GPU (green bar). Next is the dual-core CPU + GPU followed by the 3 GHz quad-core CPU + GPU. Finally, we show the overclocked 4 GHz quad-core CPU + GPU. In each case, the number of bars corresponds to the number of CPU cores, and the average CPU or GPU utilization is shown as a numerical percentage value.

One more word about CPU performance: the load may be divided between several cores in a number of these benchmarks, but the only relevant thing to notice is the level of utilization. Just because the load is distributed between all four cores does not mean that the game fully supports multi-core CPUs. Ideally, all cores would then be utilized at close to 100 percent. Load distribution and management eats some CPU power. You'll be able to see quite clearly when all four cores are really fully utilized in a game like Grand Theft Auto 4.

If the quad-core 3 GHz CPU is not fully taxed in a game, you should see lower utilization compared to the overclocked 4 GHz CPU, since the processor is even less of a bottleneck. For example, this can clearly be seen in Alien vs. Predator, a game in which the graphics card is the obvious bottleneck. This allows you to get away with having a slower CPU and not negatively impact performance.

In the second chart, you see the frame rates of our different CPU and GPU combinations as differentiated by the number of active CPU cores. This chart for Alien vs. Predator confirms what we just mentioned. The GPU is such a tight bottleneck that it hardly matters whether you have a single-core or an overclocked quad-core CPU. If you want to increase frame rates in this game, you'll have to upgrade the graphics card. The game uses 750 MB of graphics memory, which is almost as much as the GeForce GTX 460 makes available.