I’m talking about the firmware.
The firmware treats this as a separate boot environment. When you flip the switch, the Hypervisor loads a different Shared OS. This is arguably the most pro-consumer firmware decision Microsoft has made, as it turns the cheap One S into a legitimate indie game testing unit. If you repair consoles, you know the dirty secret of Xbox One firmware: The hard drive is married to the OS. Firmware Xbox One S
The Xbox One S might be "last gen," but its firmware architecture—specifically the separation of Game OS from Dashboard OS—is the reason Microsoft was able to offer backward compatibility so effectively. I’m talking about the firmware