Well I upgrade my Lenovo ThinkPad W520 from Windows 8 to Windows 10 Release Preview. The upgrade worked flawlessly (thank you Microsoft!). So I’m checking out my new digs on the new OS and opened up Windows Explorer. Very nice! The new ribbon feature add great additional functionality to the tool. But I saw that there were a few new folders added ($WINDOWS.~BT and Windows.old). Naturally I assumed that it was the folders used in upgrade process. So I decided to continue and investigate more of the new functions of the OS.
In the end, the final verdict was this build was Rock Solid!!