"The GTX 280 enables all features of the D10U processor; the GTX 260 version will consist of a significantly cut-down version of the same GPU. The D10U-30 will enable all 240 unified stream processors designed into the processor. NVIDIA documentation claims these second-generation unified shaders perform 50 percent better than the shaders found on the D9 cards released earlier this year.
The main difference between the two new GeForce GTX variants revolves around the number of shaders and memory bus width. Most importantly, NVIDIA disables 48 stream processors on the GTX 260. GTX 280 ships with a 512-bit memory bus capable of supporting 1GB GDDR3 memory; the GTX 260 alternative has a 448-bit bus with support for 896MB..."
