ATI's Radeon X1900 will be launched in early 2006 and according to The Inq it will have sixteen pipelines and 48 pixel shader units.
In the R580 case, the chip has 16 traditional pipelines that can process 16 textures while at the same time it can calculate 48 pixel data. The RV530 architecture is a good way to understand what ATI is doing now. With this chip, you have 12 pixel Shaders but just four texture memory units. Its a 3:1 ratio, as ATI believes that you need that many pixel information compared to textures.