Microsoft has talked a bit about the OS in the new Xbox One and it's major feature Snapping.  Some people have confused this with multi-tasking, which is what the PS4 does, but that isn't what's going on with the Xbox One.  The Xbox One does multi-task, but its Snap-to feature is much more complex and complicated than multi-tasking.

The HyperVisor OS sits on top of the hardware.  It has direct access to the hardware (through the HAL) and is where the Xbox One's UI runs.  The only software that is allowed to run here is authorized software as a part of the system's firmware.  The HyperVisor OS provides the core functionality for the Xbox One.   

The Apps VM is a Windows 8-based virtual machine that runs within the HyperViser OS. Access to the hardware is virtualized through the HyperVisor, subsequently the VM doesn't have direct access to hardware.  Any applications running in this environment must be certified.  The Apps VM is started with the HyperVisor OS and is always running.  If the Games VM is run full-screen, the Apps VM goes into stand-by mode and reliquishes resources.

The Games VM is an Xbox OS-based virtual machine that also runs within the HyperVisor OS.  Once again, access to the hardware is virtualized through the HyperVisor and likewise the VM doesn't have direct access to hardware.  Any games running in this environment must be properly licensed.  Unlike the Apps VM, the Games VM is started when playing a game and shutdown when the game is exited.  However, like the Apps VM, when the Apps VM is taken full-screen the Games VM will go into a stand-by mode.

To put the Snap feature into context, it is simply a feature of the Xbox One UI that allows you see the two VMs operating at the same time.  But unlike simple virtualization, the neat and unique thing about the Xbox One is how the the view of the app changes based on whether it's snapped or full-screen.  This seemingly simple capability requires a lot of sophisticated communication between independent machines that has never been seen before. 

another thing about the hyper v is that if a game developer wants to use up to 7.5 gigs if the os is under 512gb they can.  in most cases those apps will be very small so anyway.

I'm waiting to hear official numbers on the OS before I suggest any memory usage. The implication that the OS uses 3GB (1GB per each OS) is ridiculous, imho. I think the OS actually uses very little, but probably close to 2 GB is reserved for the display (GPU).

But yes, the HyperVisor OS is capable of allocating resources based on need between the two VMs. The system is even designed to throttle up or down cores and memory as needed. So if you're just watching a movie, the system can throttle down to next to no processing power, but if you receive a Skype call during that movie, it could throttle up the resources needed.

Interesting read.

Snapping this is the same feature as on Win 8 tablets I guess.

Hmm this sounds like the os would definitely use more ram than less ram. Another thing is that it sounds potentially harder to capitalize on the hardware as well, and potentially more secure/ harder to hack

does that mean no coding to the metal for xbone?

Yes. But it also means MS can in theory change all of the hardware in the X1 and games wouldn't even notice. They could run the game VMs on any hardware that matches or betters the current config.

Cool...

I believe this is their first "safe bet". Look at all the tech-demos so far, almost nothing uses more than 4gb of ram. MS will continue to improve this even more and ram-usage will be less in the next years.