Like the Playstation 3's Cell processor, the Xbox 360's Xenon processor represents a fundamentally different approach to performance than that which characterized the previous generation of consoles - and the previous generation of PCs for that matter. The Xbox 360 will rely on multithreading and procedural synthesis to make visual environments that are more immersive than anything that's possible on the present generation of either game consoles or PCs. Still, with all that pixel-pushing power at its disposal, there are a few probable flies in the Xbox 360 ointment.

Rumors and some game developer comments (on the record and off the record) have Xenon's performance on branch-intensive game control, AI, and physics code as ranging from mediocre to downright bad. Xenon will be a streaming media monster, but the parts of the game engine that have to do with making the game fun to play (and not just pretty to look at) are probably going to suffer. Even if the PPE's branch prediction is significantly better than I think it is, the relatively meager 1MB L2 cache that the game control, AI, and physics code will have to share with procedural synthesis and other graphics code will ensure that programmers have a hard time getting good performance out of non-graphics parts of the game.

Furthermore, the Xenon may be capable of running six threads at once, but the three types of branch-intensive code listed above are not as amenable to high levels of thread-level parallelization as graphics code. On the other hand, these types of code do benefit greatly from out-of-order execution, which Xenon lacks completely, a decent amount of execution core width, which Xenon also lacks; branch prediction hardware, which Xenon is probably short on; and large caches, which Xenon is definitely short on. The end result is a recipe for a console that provides developers with a wealth of graphics resources but that asks them to do more with less on the non-graphical side of gaming.