Game Watchreports that the Wii U's GPU is based on the AMD Radeon HD 4000 family line of products, which are designed around the RV770 foundation chip. This family of AMD processors saw commercial release in the PC market in 2008 and 2009. The GPU that AMD supplied for the XBox 360 has similarities to the Radeon HD 2000 line of computer graphics cards.
Assuming that none of the Radeon HD 4000 functionality was removed from the custom Wii U chip, the Wii U GPU may support Shader Model 4.1. In comparison, the XBox 360 and PS3 capabilities are at the Shader Model 3.0 level. AMD currently manufactures the Radeon HD 6000 line, featuring Shader Model 5.0.
The Wii U GPU could feature integrated Hardware tessellation that will help it smooth out rough edges on 3D models. Game Watch noted the sharp polygon edges in Nintendo's "Japanese Garden Demo" and therefore doubted the use of a tessellation stage in the tech demo.
While there is plenty of speculation on the features that the Wii U graphics chip might have, AMD has not yet released information on the GPU's clock speed, number of shader units, memory bandwidth, and other specs. These details, and other as-of-yet unknown customizations to the Wii U GPU, are also important factors in the GPU's overall performance.
Source: http://www.nintendoworldreport.com/rumor/26828
