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

32bit-64bitdllsystem32syswow64

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?

Best 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.

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C# – File getting copied to SysWOW64 instead of System32

You've run afoul of file system redirection.

Because %windir%\System32 is reserved exclusively for 64-bit applications, on 64-bit versions of Windows, 32-bit applications that attempt to access the %windir%\System32 directory are automatically and transparent redirected to the 32-bit %windir%\SysWOW64 directory.

First, make sure that your program actually does belong in the 64-bit system folder. Windows does this automatic redirection for a reason. 32-bit stuff does not go in the %windir%\System32 folder on 64-bit versions of Windows.

If you're certain that you want to be copying stuff into the 64-bit system directory, you have a couple of options. The easiest is probably to just compile your utility as a 64-bit application. Alternatively, you can tell the WOW64 redirector that you know what you're doing and not to perform the redirection by using %windir%\Sysnative instead of %windir%\System32.

Windows – Register comdlg32.dll gets Regsvr32: DllRegisterServer entry point was not found

comdlg32.dll is not a COM DLL and cannot be registered.

One way to confirm this for yourself is to run this command:

dumpbin /exports comdlg32.dll

You'll see that comdlg32.dll doesn't contain a DllRegisterServer method. Hence RegSvr32.exe won't work.

That's your answer.

ComDlg32.dll is a a system component. (exists in both c:\windows\system32 and c:\windows\syswow64) Trying to replace it or override any registration with an older version could corrupt the rest of Windows.

I can help more, but I need to know what MSComDlg.CommonDialog is. What does it do and how is it supposed to work? And what version of ComDlg32.dll are you trying to register (and where did you get it)?

Best Answer

Related Solutions

C# – File getting copied to SysWOW64 instead of System32

Windows – Register comdlg32.dll gets Regsvr32: DllRegisterServer entry point was not found

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