

It looks like this feature is designed to help protect the average Windows user, who might have outdated programs installed. If this happens, the “All of your files are exactly where you left them” screen will appear like normal–this screen always appears during major updates–but Windows will actually have removed some of your program files. If a program is known to cause crashes, bugs, or otherwise conflict with Windows, Windows may remove it to keep your system stable. Windows may remove programs during an update for compatibility reasons. That’s usually C:\Windows.old. This is also displayed as “Previous Windows installation(s)” in the Disk Cleanup application. As part of the upgrade process, Windows leaves your old Windows installation–or old Windows build–files in the “Windows.old” directory on your system drive.
