Why do 64-bit DLLs go to System32 and 32-bit DLLs to SysWoW64 on 64-bit Windows?
I would like to know when do we need to place a file under
C:\Windows\System32 or C:\Windows\SysWOW64, on a 64-bits windows system.
I had two DLL's, one for 32-bit, one for 64-bit.
Logically, I thought I'd place the 32-bit DLL under C:\Windows\System32, and the 64-bit DLL under C:\Windows\SysWOW64.
To my surprise, it's the other way around! The 32-bit one goes into C:\Windows\SysWOW64, and the 64-bit DLL goes into C:\Windows\System32.
Very confusing stuff. What's the reason behind this?
Answer
I believe the intent was to rename System32, but so many applications hard-coded for that path, that it wasn't feasible to remove it.
SysWoW64 wasn't intended for the dlls of 64-bit systems, it's actually something like "Windows on Windows64", meaning the bits you need to run 32bit apps on a 64bit windows.
This article explains a bit:
"Windows x64 has a directory System32 that contains 64-bit DLLs (sic!). Thus native processes with a bitness of 64 find “their” DLLs where they expect them: in the System32 folder. A second directory, SysWOW64, contains the 32-bit DLLs. The file system redirector does the magic of hiding the real System32 directory for 32-bit processes and showing SysWOW64 under the name of System32."
Edit: If you're talking about an installer, you really should not hard-code the path to the system folder. Instead, let Windows take care of it for you based on whether or not your installer is running on the emulation layer.