AGP TEXTURING

6/26/99

AGP Texturing: AGP texturing is a technique for reducing the memory requirements of Accelerated Graphics Processor video cards by storing less used graphics data in main memory instead of on the card. It is advertised as a way of storing larger "textures". In some cases, AGP texturing is a mode that can be turned on or off. AGP Texturing reduces costs and makes the use of large "textures" feasible.

Detractors claim that AGP Texturing reduces performance since the information to be displayed must be referenced from memory by the AGP card every time it is needed. Advocates claim that there is no performance problem with a well designed AGP card because the texturing data is requested well in advance.

Two quite different sets of comparisons seem to be thoroughly jumbled in discussions of AGP texturing. One is that of AGP texturing versus video cards that have adequate memory to store all texturing data. There is little doubt that AGP texturing hurts performance in this case. The second comparison is that of cards that use texturing data from main memory vs cards that download the data to a card with inadequate video memory before using it. In the latter case, "thrashing" of texture data in and out of video memory hurts performance and AGP texturing can improve performance by avoiding the thrashing.

One set of test data and projections indicates that AGP texturing can result in performance degradation of up to 30% in the video card performance and perhaps 10% in CPU performance relative to storing all texture data on the video card.

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