Windows.old?

[Joonyer]

Do I need this file after I have transferred all my files from my external hdd? What exactly is it for? I also have very little space after upgrading to windows 7...I think it is because of this windows.old file.

 

[KSoD]

How to retrieve files from an earlier version of Windows in Windows Vista

That will explain it all. It is basically your old install of Windows. If you need some files that link will show you how to get them. It can be deleted.