In Windows 7 and Windows Vista, if a program does not have elevated permissions to write to C:\Program Files or C:\Windows folder, Windows lets the program think it is writing there, but actually redirects the action to a Virtual Store under the AppData store in your User folder.
Usually, INI files, data files, templates are directed in such a manner.
File Virtualization in Windows 7
To take an example, I use Maxthon browser. Its favicons are meant to be stored in the following location:
However they actually get stored in the following folder:
Compatibility Files toolbar button
So if you open the first folder, you will see it as empty. But if you click on the Compatibility Files tab, immediately the latter folder is opened and you see all the favicons there.
This is called as File Virtualization.
It is one of the security feature that is not evident in Windows. The feature provides an application a virtual store where it can read and write to without compromising the system. For instance, if you have an application that tries to write to System32 then, Windows creates a virtual System32 in the user’s profile that the application can use.
Internet Explorer running in protected mode makes use of this functionality. It places a file in the virtual startup folder when you visit a web page rather than the actual Startup folder so that it does not execute upon the next boot.
This makes it possible to run applications as a standard user, even when the applications require Administrator rights. In short Windows redirects such application writes from specified secured areas to the virtual store under the user’s profile. This is something similar to Registry Virtualization.