Can an x64 application use x86 assemblies - and vice versa?

Question

My application is built as a x64 application. After moving to VS2010 I got some problems which seems to be related to some x64/x86 mismatch in referenced dlls. Now I\'m movi

Answer 1

No, a 64-bit process can only load 64-bit DLLs and a 32-bit process can only load 32-bit DLLs. What you're probably thinking of is that a 64-bit operating system can run 32-bit processes.

The main issue with .NET is that - prior to VS2010 - executable projects defaulted to "AnyCPU" which means it would load in the "native" format of the OS it's running on (so 32-bit for 32-bit versions of Windows and 64-bit for 64-bit versions of Windows). The problem with that is that if you tested your application on 32-bit Windows (say) then it could break if you load 32-bit DLLs and tried to run on 64-bit Windows.

In VS2010, they defaulted all executable projects to be "x86" (that is, 32-bit) by default which (for the most part) mitigates the problem.