Xbox 360 Backward Compatibility Details

Explaining the role ATI hardware will play in the process, Harris states:

“They have implemented compatibility purely through emulation (at the CPU level). It looks like emulation profiles for each game are going to be stored on the hard drive, and I imagine that a certain number will ship with the system. They already have the infrastructure to distribute more profiles via Live, and more and more can be made available online periodically.”

“Emulating the CPU isn’t really a difficult task. They have three 3GHz cores, so emulating one 733MHz chip is pretty easy. The real bottlenecks in the emulation are GPU calls – calls made specifically by games to the nVIDIA hardware in a certain way. General GPU instructions are easy to convert – an instruction to draw a triangle in a certain way will be pretty generic. However, it’s the odd cases, the proprietary routines that will cause hassle.”