run asp.net 3.5 sites on asp.net 4.0 without changing code\web.config

Is it possible开发者_StackOverflow中文版?

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Yes, if you have .NET 3.5 installed. Otherwise you will have to upgrade since .NET 4.0 has its own CLR.

See ASP.NET Side-by-Side Execution Overview : http://msdn.microsoft.com/en-us/library/a99txfy5.aspx

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There are subtle breaking-changes, many of which are for he better IMHO.

You'll need to set up seperate application pools targetting the appropriate framework and placing your 3.5/4.0 sites in the right pool.

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Yes. Both options are available in VS 2010. Just take care of functionality like ajax. It may stop you running old apps in new C #.