32bit 64bit - Why do 64-bit DLLs go to System32 and 32-bit DLLs to SysWoW64 on 64-bit Windows?

Question

I would like to know when do we need to place a file under

C:WindowsSystem32 or C:WindowsSysWOW64, 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:WindowsSystem32, and the 64-bit DLL under C:WindowsSysWOW64.

To my surprise, it's the other way around! The 32-bit one goes into C:WindowsSysWOW64, and the 64-bit DLL goes into C:WindowsSystem32.

Very confusing stuff. What's the reason behind this?

Answer 1

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.