32-bit and 64-bit Application Data in the Registry (Windows)

32-bit and 64-bit Application Data ...

32-bit and 64-bit Application Data in the Registry

On 64-bit Windows, portions of the registry entries are stored separately for 32-bit application and 64-bit applications and mapped into separate logical registry views using the registry redirector and registry reflection, because the 64-bit version of an application may use different registry keys and values than the 32-bit version. There are also shared registry keys that are not redirected or reflected.

The parent of each 64-bit registry node is the Image-Specific Node or ISN. The registry redirector transparently directs an application's registry access to the appropriate ISN subnode. Redirection subnodes in the registry tree are created automatically by the WOW64 component using the name Wow6432Node. As a result, it is essential not to name any registry key you create Wow6432Node.

The KEY_WOW64_64KEY and KEY_WOW64_32KEY flags enable explicit access to the 64-bit registry view and the 32-bit view, respectively. For more information, see Accessing an Alternate Registry View.

To disable and enable registry reflection for a particular key, use the RegDisableReflectionKey and RegEnableReflectionKey functions. Applications should disable reflection only for the registry keys that they create and not attempt to disable reflection for the predefined keys such as HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER. To determine which keys are on the reflection list, use the RegQueryReflectionKey function.

Note: When using the registry API (e.g., RegOpenKeyEx and RegEnumKeyEx) in a 32-bit application, Wow6432Node acts like a symbolic link that loops back to the same 32-bit hive. It does not map into the 64-bit hive as you might think.

For example, walking the registry tree down to HKLM\Software\Wow6432Node in a 32-bit application loops back to HKLM\Software. The result is infinite recursion: HKLM\Software\Wow6432Node\Wow6432Node\Wow6432Node\..., etc.

If you want to view the 64-bit registry hive in 32-bit code you must open HKLM\Software using KEY_WOW64_64KEY. Do not try to open Wow6432Node; it will not work.

As a general rule you should ignore any result from RegEnumKeyEx that returns "Wow6432Node". It is a magic name that triggers special behavior by the registry API.

Windows Server 2008: In the 32-bit hive the registry key HKLM\Software\Wow6432Node is hidden from RegEnumKeyEx. This fixes the infinite recursion bug described above. The hidden key still exists and the infinite recursion can still happen, but only if you explicitly open the key.

See Also