2. The Impact Of The Fill Rate

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After taking care of 'the platform', the 3D-card is the only thing left. The 'fill rate' describes the amount of pixels that a 3D-solution can render in a given amount of time. We all know that a frame consists of a certain amount of little dots, called 'pixels'. Each screen resolution requires a certain amount of pixels. The common resolution 640x480 is made of 307,200 pixels, while a high resolution as 1600x1200 requires 1,920,000 pixels. The 3D-chip has to 'render' each pixel of a frame before the frame can get displayed. The 'frame rate' is defined as the number of frames that can be displayed in a certain amount of time. It's easy to see that it requires a lot more rendering performance to supply a certain frame rate at a high resolution than at a low resolution. This is why typically 3D cards score high frame rates at 640x480 and lower frame rates at 1600x1200. After all the 3D-chip has to render more than 6 times as many pixels for each frame at 1600x1200 than at 640x480.

Nowadays 3D-chips have several rendering pipelines that can operate in parallel. Such a pipeline is usually able to render one pixel per clock cycle. Thus the maximal pixel fill rate is the 3D-chip clock times the number of rendering pipelines times the number of chips in case that more than one 3D-chip is being used on a 3D-card. A typical example would be NVIDIA's new GeForce2 GTS chip, which is clocked at 200 MHz and which comes with 4 rendering pipelines. 4 pixels x 200 million/s = 800 million pixel/s. 3dfx's Voodoo5 5500 is clocked at 166 MHz, each chip has two rendering units and the card comes with two chips. 2 pixels x 166 million/s x 2 = 667 million pixel/s.