The .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.
The .NET Framework 4 works side by side with older Framework versions. Applications that are based on earlier versions of the Framework will continue to run on the version targeted by default.
The Microsoft .NET Framework 4 provides the following new features and improvements:
Improvements in Common Language Runtime (CLR) and Base Class Library (BCL)
Performance improvement including better multicore support, background garbage collection, and profiler attach on server.
New memory mapped file and numeric types.
Easier debugging including dump debugging, Watson minidumps, mixed mode debugging for 64 bit and code contracts.
Innovations in the Visual Basic and C# languages, for example statement lambdas, implicit line continuations, dynamic dispatch, and named/optional parameters.
Improvements in Data Access and Modeling
The Entity Framework enables developers to program against relational databases using .NET objects and Language Integrated Query (LINQ). It has many new features, including persistence ignorance and POCO support, foreign key associations, lazy loading, test-driven development support, functions in the model, and new LINQ operators. Additional features include better n-tier support with self-tracking entities, customizable code generation using T4 templates, model first development, an improved designer experience, better performance, and pluralization of entity sets.
WCF Data Services is a component of the .NET Framework that enables you to create REST-based services and applications that use the Open Data Protocol (OData) to expose and consume data over the Web.