Pixel shading is programmable pixel processing, and vertex shading is programmable vertex processing. They are being called shaders, but that's not an accurate naming convention. Programmable pixel/vertex processing is more accurate, but perhaps the term "shaders" was considered more enchanting.
The opposite of programmable processing is fixed-function processing. With fixed-function processing, vertices and pixels can only be processed in a small number of ways that the hardware and graphics API are designed to process. With programmable processing, custom "shaders" can be written using pixel and vertex processing languages. In other words, shaders allow developers more freedom, flexibility, and customization for graphics. That can lead to better image quality and/or faster performance compared to fixed-function processing.
Multiple pixel and/or vertex pipelines are for parallel processing. Just like doubling the clock speed can double maximum performance, doubling pipelines can also double maximum performance. For example, a single pipeline running at 400 MHz should have similar performance to two pipelines running at only 200 MHz, if no other limiting factors (such as bandwidth usage) play a role.
HANK
Date: 2002-01-23
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