The HKEY_CURRENT_USER subtree contains the user profile for the user who is currently logged on to the computer. The user profile includes environment variables, personal program groups, desktop settings, network connections, printers, and application preferences. The data in the user profile is similar to the data stored in the Win.ini file in Windows 3. x.
The HKEY_CURRENT USER subtree does not contain any data. It just stores a pointer to the content of the HKEY_USERS\ Security ID (SID) of current user subkey. Therefore, the content of that subkey also appear in HKEY_CURRENT_USER, and it can be viewed and changed in either location. This subtree provides easier access to the data.
A new HKEY_CURRENT_USER subtree is created each time a user logs on. The data for the subtree comes from the profile of the current user. If no profile is available, the subtree is built from the user profile settings established for a default user, which are stored in System drive \Documents and Settings\Default User (WINNT)\Ntuser.dat.