What is left behind with a Windows XP to Windows 7 upgrade? (Windows.old)?

Question

My understanding is to use Windows 7 upgrade media you must install and activate Windows Vista or Windows XP. In the case of upgrading from Windows XP a "clean install" is performed, but in reading about this, it sounds like this may just be overwriting the Windows XP installation, as it talks about the old Windows being moved to a Windows.old folder. It sounds like the same kind of thing you get when you install Windows over itself, which if you are familiar with that you know it leaves all kinds of junk from the previous installation.

This leads me to believe that this won't be a true clean install, in terms of it being identical to performing a non-upgrade install. What is this Windows.old folder, and what other "junk" will be left behind from the Windows XP install?

Answer 1

It doesn't overwrite anything. The complete contents of your installation drive are moved to the Windows.old folder, despite the name. So you have a tree which looks approximately like this:

C:
+--Users
|  +--Me
+--Program Files
+--Windows
+--Windows.old
   +--Documents and Settings
   +--Program Files
   +--Windows

So your installation is as clean as it can get, but you still have everything you had on that partition before lying around in Windows.old. If you don't need that anymore (and who needs XP when installing Win 7 :-)) you can simply format the partition or delete and re-create it.

Answer 2

You can do a clean install using an upgrade DVD, it's the same Windows inside. So, just erase the old Windows and do a clean install, otherwise you'll just have junk on your hard drive from a previous install. You can read more about it in this blog post by Paul Thurrott about upgrade disks.

You don't need the old stuff from the Windows directory, since it's not really an upgrade. A real upgrade can only be done from Vista to 7.

Answer 3

Junk is left when you install without erasing hard drive. All Windows components will be new, but there will be leftovers of old OS everywhere on hard drive. Windows 7 will function as new (except for fragmentation issues).

To get truly clean installation, just hit format on disk selection menu during Windows 7 setup.