A hive is a logical group of keys, subkeys, and values in the registry that has a set of supporting files containing backups of its data.
Most of the supporting files for the hives are in the %SystemRoot%\System32\Config directory. These files are updated each time a user logs on.
Registry hive Supporting files
HKEY_CURRENT_CONFIG System, System.alt, System.log, System.sav
HKEY_CURRENT_USER Ntuser.dat, Ntuser.dat.log
HKEY_LOCAL_MACHINE\SAM Sam, Sam.log, Sam.sav
HKEY_LOCAL_MACHINE\Security Security, Security.log, Security.sav
HKEY_LOCAL_MACHINE\Software Software, Software.log, Software.sav
HKEY_LOCAL_MACHINE\System System, System.alt, System.log, System.sav
HKEY_USERS\.DEFAULT Default, Default.log, Default.sav
Detail URL: http://msdn.microsoft.com/en-us/library/windows/desktop/ms724877%28v=vs.85%29.aspx
