I have an existing C# application written for .NET 2.0 and targetting AnyCPU at the moment. It currently references some third party .NET DLLs which I don't have the source for (and I'm not sure if they were built for x86, x64 or AnyCPU).

If I want to run my application specifically on a 64 bit Windows OS, which platform should I target in order for my app to run without errors? My understanding at the moment is to target:

• x86: If at least one third party .NET dll is built for x86 or use p/Invoke to interface with Win32 DLLs. Application will run in 32 bit mode on both 32 bit and 64 bit OSes.
• x64: If all third party .NET dlls are already built for x64 or AnyCPU. Application will only run in 64 bit OSes.
• AnyCPU: If all third party .NET dlls are already built for AnyCPU. Application will run in 32 bit mode on 32 bit OSes and 64 bit on 64 bit OSes.

Also, am I right to believe that while targetting AnyCPU will generate no errors when building a application referencing third party x86 .NET DLLs, the application will throw a runtime exception when it tries to load these DLLs when it runs on a 64 bit OS.

Hence, as long as one of my third party DLLs is doing p/Invoke or are x86, I can only target x86 for this application?