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Migrating some 32 code to 64-bits in a new machine, I had to "soft" adapt some code for at least allow compilation. For that, I registered old 32 libraries (mscomctl.ocx, mscal.ocx) and had a need to add too FM20.dll.

Although VBA swear that it is at C:\WINDOWS\system32:

VBA reference dialogue

I could not see it, of course with hidden files enabled: enter image description here

But if I navigate through an Add reference Dialog, I can see it: enter image description here

BTW, one of my applications uses the FM20.dll copy located at

\Program Files (x86)\Microsoft Office\root\vfs\SystemX86

and it is possible to see it through Windows explorer; this is a different verison (00086 vs 20386): enter image description here

I saw older questions like this and this but had no help understanding why it is this way, and for which other libraries we can expect this behavior.

Mark Rotteveel
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Marcelo Scofano Diniz
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    These apps were written a long time ago, before there was a 64-bit version of Windows. Look in c:\windows\syswow64, the home for 32-bit DLLs like fm20.dll. That these apps don't know that it is actually located in syswow64 is very much by design, that's why these ancient apps can still work correctly. https://learn.microsoft.com/en-us/windows/win32/winprog64/file-system-redirector – Hans Passant Jul 31 '19 at 21:51
  • @HansPassant, solved; I never had heard of File System Redirector before. thanks! – Marcelo Scofano Diniz Aug 01 '19 at 03:04
  • I now see that the anomaly that I complain about is caused by the confusing and crazy decision made years ago by MS. To everyone who comes here through this strange behavior, I want to redirect to this answered question, which exhausts the subject: [Why do 64-bit DLLs go to System32 and 32-bit DLLs to SysWoW64 on 64-bit Windows?](https://stackoverflow.com/questions/949959/why-do-64-bit-dlls-go-to-system32-and-32-bit-dlls-to-syswow64-on-64-bit-windows?rq=1) – Marcelo Scofano Diniz Aug 01 '19 at 19:03
  • Although I strongly agree that the answer is the same, I do not think that the question is duplicated, because no one there cited the strange behavior that is described at the title, and it was this behavior that bring me here to ask it; so, maybe it'll be useful for other people if the question remains as it is now; but, it's up to the community. – Marcelo Scofano Diniz Aug 02 '19 at 00:32

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