A very interesting read from Richard Leadbetter at Eurogamer:
Up until recently, both Xbox One and PlayStation 4 have reserved two entire CPU cores (out of eight available) in order to run the background operating system in parallel with games. Since October, Microsoft has allowed developers access to 50 to 80 per cent of a seventh processing core - which may partly explain why a small amount of multi-platform titles released during Q4 2014 may have possessed performance advantages over their PS4 counterparts in certain scenarios.
However, there’s no such thing as a free lunch, and the additional CPU power comes with conditions and trades attached - however, there is the potential for many games to benefit. Firstly, developers need to give up custom, game-specific voice commands in order to access the seventh core at all, while Kinect’s infra-red and depth functionality is also disabled. Secondly, the amount of CPU time available to developers varies at any given moment - system-related voice commands (“Xbox record that”, “Xbox go to friends”) automatically see CPU usage for the seventh core rise to 50 per cent. At the moment, the operating system does not inform the developer how much CPU time is available, so scheduling tasks will be troublesome. This is quite important - voice commands during gameplay will be few and far between, meaning that 80 per cent of the core should be available most of the time. However, right now, developers won’t know if and when that allocation will drop. It’s a limitation recognised in the documentation, with Microsoft set to address that in a future SDK update.
The concessions Microsoft has been making to the Xbox One (revised DRM model, “dis-Kinect”, price-drop, bundles, and now opening the seventh processing core) are admirable, and considering the recent spike in sales, certainly make for an interesting future for the console war. However, these are just that — concessions. Sony has continued to stay the course with compelling hardware and a simple story. Not to mention this is another hit against Kinect and the original vision of Xbox One.