The Chip

The Rage6C core is unlike any other core that ATI has designed. The core is not a refresh of the aging Rage128 core but a new product completely. Not much has changed since the Radeon's announcement in April, but let's review what we already know and see what one item has changed.

For the most part, what ATI said they would deliver with a Radeon card has found its way into the shipping cards. As suspected, the architecture of the chip is .18 micron with two rendering pipelines with three texture units per pipeline for a total output of 6 texels per clock. Having 2 less texels per clock of the GeForce 2 GTS, with its four pipelines and 2 textures per pipe, in theory the Radeon is crippled by these pipelines.

The reason for this is that dual texture games, such as Quake III Arena, will actually end up not using one of the textures in the Radeon's three texture pipeline. The GeForce 2 GTS's pipeline does not encounter this problem in dual texture games since each pipeline is able to use both texture units for rendering.

The tables become turned, however, when a scene being rendered has three or more textures per pixel. In this case, the Radeon's pipeline architecture is capable of using each texture unit in rendering, resulting in one pass per pixel rendered. The GeForce 2 GTS, on the other hand, relies on two of its pipelines to render a single pixel in a three textured game, with one pipeline rendering two textures and a second one rendering the third, leaving the second texture in the second pipeline wasted. Although few games use 3 textures per pixel, ATI is betting on this to become the embraced standard.

The second part to ATI's decision to use a three texture unit pipeline comes from the fact that texels simply do not add speed due to memory bandwidth limitations. This can be seen in the GeForce 2 GTS: while the GPU is capable of pushing out 1.6 gigatexels per second, this fill rate is never seen due to the extensive memory bandwidth limitations encountered.

Index More of the Chip, Part I

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