What is the compatibility on .NET 4.0?

Question

We have several .NET applications developed in .NET 3.5 (Windows services, web applications, and WCF services) in different servers.

I'd like to migrate to .NET 4.0 and use VS.NET 2010.

• Does VS.NET 2010 compiles to .NET 3.5 to avoid full simultaneous migration, being able to stop using VS.NET 2008 but maintaining some applications in the previous version?

• Can I uninstall the .NET < 4.0 runtime and have only .NET 4.0 in my servers? Does it run applications compiled to previous framework versions?

Answer 1

1. Yes, it does
2. No you can't, the other runtime versions have to be installed. But you are able to run < 4.0 in a 4.0 .net process (e.g. a class library or so). msdn

Answer 2

Visual Studio 2010 can target versions 2.0, 3.0, 3.5 and 4 of the .NET Framework. If a version of the framework is installed on your computer but doesn't show up in Visual Studio 2010, install .NET 3.5 SP1.

When opening a solution created in a previous version, Visual Studio will convert the solution to the new format. This means that everyone working on a solution will have to use the same version of Visual Studio. However, with the possibility to target different framework versions, this shouldn't be a problem.