Does KEY_WOW64_64KEY really affect 32-bit Windows?

Question

It seems that specifying KEY_WOW64_64KEY ( link ) when accessing the registry key under 32-bit Windows XP has no effect - this does not cause an error, and the key opens as if you did not have the flag set.

I know that Windows 2000 throws an error when this flag is detected.

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

Is there a Microsoft link that defines every version of Windows behavior for this flag? In particular, I would like something to confirm my assumption that it does not affect 32-bit Windows post-2k at all.

Answer 1

I cannot talk with Windows 2000 or XP, but I know that in Vista and above KEY_WOW64_64KEY opens a registry key in a 64-bit registry if it is a 64-bit OS and 32-bit registry if it is a 32-bit OS.

Answer 2

I tested the 32-bit version of Windows XP and it seems to work fine.

Answer 3

In addition, you should usually avoid this key - WOW64 provides a fairly complete “illusion” for 32-bit applications; just write your application on 32-bit without this flag, and it will still work on WOW64. Do not try to use this flag (and other mechanisms) for "64-bit compatibility".