As I understand it the 2010 Mac Pro has a triple-channel memory controller. So I am wondering... Why the single-CPU has 4 memory slots, instead of 3 (or, better yet, 6)? It seems an odd design choice. I'm also not clear what the penalty is for using the 4th slot which, presumably, takes it out of triple-channel mode if you have to use matched pairs rather than a set of 3. Is it anything to worry about in real-world performance terms? Matt.