Shoutbox

Active Directory... (or Novell eDirectory)

Your credentials are stored on a central server (Directory server). When logged in, the OS (Windows) maps a drive with your personal files and/or sets the user profile folder to a network share which insures that your files and settings follows you everywhere you go.

Or... You are on a terminal client. In such case, you are not working on the computer you are on but control a session on the terminal server.