"Out-of-the box, a Windows system automatically shares the root of every hard drive on the machine as
$ (so you get C$, D$, A$, etc).
The shares are ACL'ed so that only members of the local administrative group can access them, and they're hidden from the normal enumeration UI (they're included in the enumeration APIs but not in the UI (as are all shares with a trailing $ in their name)."
Thursday, May 26, 2005
Larry Osterman's WebLog : Why does Windows share the root of your drive?: