4.1. The New CLR
The last two releases of.NET (3.0 and 3.5) have been additive releases that build on top of the functionality available in CLR version 2.0 (see Figure 4-1).
Figure 4.1. CLR releases
.NET 4.0 however has a new version of the CLR! So you can happily install .NET 4.0 without fear that it will affect your existing .NET applications running on previous versions of the framework.
4.1.1. ASP.NET
When using IIS7, the CLR version is determined by the application pool settings. Thus, you should be able to run .NET 4.0 ASP.NET applications side by side without fear of affecting existing ASP.NET sites.
4.1.2. What Version of the CLR ...
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