When the registry is opened there are five visible hives. However, there are only two main hives HKEY_USERS and HKEY_LOCAL_ MACHINE.

All the other keys are subkeys of HKEY_LOCAL_MACHINE and HKEY_USERS:
 

• HKEY_CURRENT_USER contains information on the user that is currently logged in. It is a subkey of HKEY_USERS. The other user accounts (including HKEY_CURRENT_USER) are all stored under HKEY_USERS; however, they are stored in a GUID format making it difficult to determine what user the key belongs to. When a user logs in, their respective key is loaded to the HKEY_CURRENT_USER hive.
• HKEY_CURRENT_CONFIG is a shortcut to HKEY_LOCAL_MACHINE\CurrentControlSet\Hardware Profiles\Current.
• HKEY_CLASSES_ROOT is a shortcut to HKEY_LOCAL_MACHINE\Software\Classes.

To query the three "other" hives, use the path that was specified under each of the two main hives.