In a recent move, Siligon Graphics (SGI) decided to fill a patent infringement lawsuit against ATI.
The ingringed patent, No. 6,650,327 (filled in 1998, granted in 2003), is named " Display system having floating point rasterization and floating point framebuffering" and deals with 16 bits (s10e5) and 32 bits floating point frame buffers as well as with hardware floating point raster operations.
Read the press release here