I've built a Windows service as “Any CPU”. Why does it run in 32-bit mode on my 64 bit machine? [duplicate]

Answer 1

If the app exe which starts the CLR is compiled as:

1. x64: AnyCPU assemblies with use JIT to compile x64 versions of the assemblies (slow). x86 assemblies will get a BadImageFormatException.
2. x86: AnyCPU assemblies JIT to x86. x64 assemblies will get a BadImageFormatException.
3. AnyCPU: .Net will default to x86. See above.

I often use a starter application, where I explicitly compile the .exe as x64 or x86 and ship x86 and x86 versions of the .msi. This is probably the easiest route - The performance gain is generally worth the overhead of managing additional files.

Alternatively, you can use ngen during the setup process, which will do all the JIT stuff when the application is installed. You will notice improved start-up times for your application.

Also, as I recently discovered with x86 applications, there is a 2GB memory limit for .net applications. This occurs even when you have 4gb of ram on your x86 and have heaps of memory left over.