<Dl> <Dt> HKEY_CLASSES_ROOT (HKCR) </Dt> <Dd> Abbreviated HKCR, HKEY_CLASSES_ROOT contains information about registered applications, such as file associations and OLE Object Class IDs, tying them to the applications used to handle these items . On Windows 2000 and above, HKCR is a compilation of user - based HKCU \ Software \ Classes and machine - based HKLM \ Software \ Classes . If a given value exists in both of the subkeys above, the one in HKCU \ Software \ Classes takes precedence . The design allows for either machine - or user - specific registration of COM objects . </Dd> </Dl> <Dt> HKEY_CLASSES_ROOT (HKCR) </Dt> <Dd> Abbreviated HKCR, HKEY_CLASSES_ROOT contains information about registered applications, such as file associations and OLE Object Class IDs, tying them to the applications used to handle these items . On Windows 2000 and above, HKCR is a compilation of user - based HKCU \ Software \ Classes and machine - based HKLM \ Software \ Classes . If a given value exists in both of the subkeys above, the one in HKCU \ Software \ Classes takes precedence . The design allows for either machine - or user - specific registration of COM objects . </Dd> <Dl> <Dt> HKEY_USERS (HKU) </Dt> <Dd> Abbreviated HKU, HKEY_USERS contains subkeys corresponding to the HKEY_CURRENT_USER keys for each user profile actively loaded on the machine, though user hives are usually only loaded for currently logged - in users . </Dd> </Dl>

Which registry root key stores information about registered applications including file associations