The Radeon X1900 (R580) is architecturally very similar to the Radeon X1800 (R520), so we recommend perusing this article for a more comprehensive look at the features common to both GPUs, like the 512-bit Ring Bus Memory Controller, Shader Model 3.0 support and AVIVO.
This high level architectural block diagram above highlights the main feature of the Radeon X1900 -- its 48 pixel shader processors. Unlike the Radeon X1800 which has 16 pixel shader processors, and the GeForce 7800 GTX which has 24, the Radeon X1900 has a full 48 pixel shader processors in the first stage of the 3D pipeline.
With the R520, ATI de-coupled the individual stages in the 3D pipeline, which gave them the ability to have an asymmetrical number of pixel shader processors and ROPs, or "Render Backends". So basically, what ATI did with the R580, was take the existing R520 architecture and tripled the number of pixel shader processors in the first stage of the pipeline. But the rest of the chip is largely unchanged. The R580 still has the same 8 vertex shaders, 16 texture units, 16 ROPs, and the same memory controller. The large number of pixel shader processors gives the X1900 a ton of resources for executing pixel shader code, but the in situations where pixel shading is not a limiting factor in performance, the X1900 should perform similarly to the X1800 XT. Just about every new gaming title and many titles released over the last couple of years, make use of pixel shaders however, so the additional 60 million transistors used on the X1900 to increase the number of shader processors should certainly be put to good use, especially with newer gaming titles that make heavy use of longer, more complex shaders.
The pixel shader processors are grouped together in quads. The Radeon X1900 has twelve of these quads for executing pixel shader code. The components of each quad and their respective computational capabilities are outlined above. Over an above the number of pixel shader processors, ATI had made a couple of other advancements with the R580 as well. We'll talk about those changes next.