FiringSquad has posted up an interesting article about Fillrate vs. CPU. Here a clip:

Have you ever noticed how your system suddenly performs worse when you increase the resolution? Wonder why that never happens to someone running some cheesy old K6/233 combined with a Voodoo3 3000 PCI? They could be running Quake3 in 1024x768 or 640x480 and still get 20-some FPS? That's because the video card relies on the CPU to deliver it the information it needs to draw a scene. The video card can't draw Sarge firing a rocket at Klesk if it doesn't know where Sarge is, how he's lit, where he's aiming, what the surrounding level looks like, etc. The video card can't render the scene until the CPU sends over all of the necessary information.

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