For a comprehensive list of enhancements to CLR and BCL go here.Easier debugging including dump debugging, Watson minidumps, mixed mode debugging for 64 bit and code contracts.New memory mapped file and numeric types.Performance improvement including better multicore support, background garbage collection, and profiler attach on server.Improvements in Common Language Runtime (CLR) and Base Class Library (BCL).NET Framework 4 provides the following new features and improvements: Applications that are based on earlier versions of the Framework will continue to run on the version targeted by default. NET Framework 4 works side by side with older Framework versions. NET Framework is Microsoft's comprehensive and consistent programming model for building applications that have visually stunning user experiences, seamless and secure communication, and the ability to model a range of business processes.
