Question: It *appears* that specifying the `KEY_WOW64_64KEY` flag ([reference](http://msdn.microsoft.com/en-us/library/aa384129%28VS.85%29.aspx)) when accessing a registry key under 32-bit Windows XP has no effect - that is, no error is thrown, and the key is opened as if you hadn't had the flag set.

I know Windows 2000 throws an error when it encounters this flag.

I want to make sure my app is compatible with as many versions of windows (2k and later) as possible. 

Is there a Microsoft reference that specifies each version of Windows' behaviour for this flag? In particular, I'd like something that validates my assumption that it has no effect at all on post-2k 32-bit Windows.

Answer: 
According to this Windows page:

<https://learn.microsoft.com/en-us/windows/win32/sysinfo/registry-key-security-and-access-rights?redirectedfrom=MSDN>

Both

```
KEY_WOW64_32KEY (0x0200)

KEY_WOW64_64KEY (0x0100)

```

will be ignored on 32-bit Windows.

And those flags are not supported on Windows 2000.
I have tested on Windows XP 32 bit, and it seems to work OK.