Hive Description
HKEY_CURRENT_USER Contains profile information for the user currently logged on. This information includes desktop settings and program settings specific to the user.
HKEY_USERS Contains all user profiles. HKEY_CURRENT_USER is a subkey of this hive, though it is recommended that you make the changes to the current user hive.
HKEY_LOCAL_MACHINE Contains configuration information particular to the computer for any user.
HKEY_CLASSES_ROOT Contains information on how files relate to the program that uses them. Is a subkey of HKEY_LOCAL_MACHINE\Software.
HKEY_CURRENT_CONFIG Contains information about the hardware profile used by the computer at startup.

Table 1 Dig Into the Registry.
The five hives of the Registry behave similarly to tables in a database, with each acting as a discrete container for different types of information.