In an interview with Eurogamer, two Xbox One architects revealed that a “conservative” 10 percent of the Xbox One’s GPU was reserved for system processing, which includes features such as Kinect processing, dashboard switching, and snap mode. This reserved 10 percent of the GPU’s capabilities are currently inaccessible to developers, but Microsoft has stated that they will eventually open up the partition for developers some time after launch.

Note that since some of the GPU will still be required for rendering system components, the partitioned section of the GPU will be time-shared between system content and title content. To ensure that graphical fidelity of title content isn’t adversely affected by the constant switching between processes, two render pipes will allow for title content to be rendered with a high priority while concurrently rendering system content at a low priority. While this may appear to slow down system capabilities in order to improve title content, the reality is that the entire partitioned 10% was likely higher than the actual use of the system processes (hence the use of the term conservative); thus, decreasing the percentage of the GPU available for system functionality likely won’t cause any slow down in the system content of the Xbox One.

Sources: Eurogamer