From a confirmed X1 dev on reddit
Somebody had PM'ed me earlier linking to the Ars article on how the PS4 has a big advantage over the Xbox one due to hUMA. This was apparently said by some AMD marketing manager.
I haven't heard of hUMA until today, so I went to look it up. The way I understand it is that in addition to having unified memory access (shared memory between CPU and GPU), which allows the GPU to read CPU memory, it is also a coherent cache system. To quote Ars, "CPU and GPU will always see a consistent view of data in memory. If one processor makes a change then the other processor will see that changed data, even if the old value was being cached."
I remember reading something on this when I got my first alpha kit. I pulled up a couple of our internal white papers and it's pretty clear that this was the exact implementation in the Xbox One's memory system.
Also I couldn't find any sources where Marc Diana actually said PS4 supports hUMA and Xbox One doesn't. Every media outlet reporting on this seems to source a single German article which I'm not inclined to believe.
http://www.reddit.com/r/xboxone/comments/1kv1xd/xbox_one_has_its_own_coherency_solution_similar/cbswrn3
