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 HKEY_USERS\<Security ID (SID) of current user>. As such, the data stored in this subkey of HKEY_USERS appears in HKEY_CURRENT_USER. The data can be viewed and changed directly and programmatically in either location.
A new HKEY_CURRENT_USER subtree is created each time a user logs on. The data for HKEY_CURRENT_USER comes from the profile of the current user. If no profile is available, HKEY_CURRENT_USER is built from the user profile settings established for a default user, stored on the System drive\Documents and Settings\Default User (WINNT)\Ntuser.dat.