What's going on under the covers when calling a .NET 2.0 assembly from a .NET 4.0 website

I have a .NET 4.0 web application that references various assemblies, some of which are .NET 4.0, .NET 3.5 and .NET 2.0. Everything works fine, but it makes me curious about what is actually occuring within the application.

And since everything seems to work, why would I want/need to 开发者_StackOverflow中文版upgrade the .NET 2.0 assemblies.

By and large, the .Net 4.0 assemblies are a superset of all the previous versions.

MSVS2008 was the first version that allowed you to compile for an earlier version of .Net (you could select 2.0, 3.0 or 3.5 compatibility).

If you don't happen to be using any .Net 4.0 features, or .Net 3.0 web services, then I'm unsurprised your application will probably run in a .Net 2.0 environment.

But I wouldn't necessarily COUNT on it.

PS: Get a copy of Net Reflector. It used to be free; I understand it's now (a nominal) $35.00. But it's a great tool, and it'll help with precisely this kind of issue:

http://reflector.red-gate.com/