In Windows 10, the folder $WINDOWS.~BT contains the previous installation of Windows. Folders $Windows.~BT and $Windows.~WS in Windows 10 In theory, the operating system is supposed to remove these files automatically as they are no longer required, but there are cases when they are still stored on your hard disk. However, as the free upgrade period is over now, there is no way you can use these files to upgrade to Windows 10, even if you like the idea. When receiving the user’s approval to proceed with the installation, the operating system starts working with the corresponding files it has downloaded.
During the free upgrade from Windows 7 or 8 to Windows 10 the operating system automatically downloads installation files and saves them to the folder $WINDOWS.~BT.
