Microsoft today provided a lengthy explanation of two related and key new features called PC Reset and PC Refresh. The post on Building Windows 8 goes into quite a bit of detail, expanding greatly on the information I provided previously in my Windows 8 Developer Preview overview. There, I wrote:
PC recovery. The Windows 8 recovery stuff is awesome and is going to represent a major milestone in PC reliability. There are two major options to note, PC Refresh and PC Reset. With Reset, you get a full reset, and the entire PC is wiped out and reinstalled from scratch. This process takes a few minutes currently and will return the PC to its factory condition; it doesn't require any external discs or USB key. With Refresh, your files, data, favorites, personalization, and metro style apps are all backed up, the OS is wiped out and replaced, and then everything is reapplied to the PC, leaving you with a pristine, running copy of Windows with everything (except for classic applications) exactly the way they were before. It currently takes 4 to 5 minutes.
Anyway, the post has a lot more detail, as always, if you're morbidly curious. Plus, there's a video in there as well.