In the press session about AMDs K10 architecture Guiseppe Amato also gave some additional info on the AMD Fusion project. He explained that it is very possible, that Fusion products might come in the form of multi-chip modules, also known as MCMs.

Amato noted, that multi-chip modules are more flexible in comparison to single dies. He gives a very simple example. To paraphrase, Amato says AMD could ship a CPU with integrated DX10 graphics functionality. Once DX11 comes out,  AMD would have to do a complete chip redesign. When implemented as a MCM, the company can keep the CPU part as is and just exchange the graphics core for a new one – all implemented on a single package.

Integration into the main silicon die only makes sense, if the functionality doesn't change for a at least a year. Ironically, efficiency advantages were always touted by Intel when talking about their MCM implementations of dual- and quad-core CPUs. However, AMD adds one interesting factor, a partial upgrade of a product with the other chip left untouched.