Check the size of the Registry ad hives

source: http://superuser.com/questions/374270/determine-size-of-registry

%windir%\System32\config and %USERPROFILE%\NTUSER.DAT. The config folder will be hidden, but contains all the registry hives, EXCEPT for the HKEY_CURRENT_USER, which is the NTUSER.DAT file

source: http://superuser.com/questions/374270/determine-size-of-registry