If you’re familiar with Windows Media Center or Zune, you may know that these applications use a system called monitored folders to watch, or monitor, folders in the file system for new or changed files. The system used by Windows Libraries is functionally identical. If anything changes in a physical folder that is being monitored by a Library, that change will be reflected in the Library.
Now, where does Library exist? As it turns out, the Libraries folder can be found at C:\Users\your username\AppData\Roaming\ Microsoft\Windows\Libraries, which is hidden by default. Like special shell folders from Windows past, the Libraries folder is really just a special location in the shell namespace and is there for your convenience.
In addition to the pinned tray shortcut, you can access this folder at any time, in any Windows Explorer window, by clicking the Libraries link in the navigation pane.
Here’s how Libraries are different, from a usage standpoint:
Libraries look different than folders: If you compare a typical Library window and a typical folder window side-by-side, you’ll see a few subtle but important differences. Libraries include a header area that lists the name of the library and links for Includes and Arrange by, as shown in Screenshot below.
These links provide access to additional Library functionality. But as important as the UI difference is, it’s equally important to understand that the header area you see in a Library is available continuously as you drill down into the folders it “contains.” You won’t see this header or gain access to its functionality if you access the same shell locations via normal folders.
Libraries are collections: By default, each of the four Libraries that ship with Windows 7, Documents, Music, Pictures, and Videos, collects, or aggregates, content from two physical locations on your hard drive and displays them in a single location.
For example, the Documents library collects content from your My Documents folder (C:\Users\your username\My Documents) and the Public Documents folder (C:\Users\Public\Public Documents). You are free to add and remove the folders that a library monitors for content.