.NET Framework 4.0

.NET Framework 4.0 was launched alongside Microsoft Visual Studio 2010 on April 12, 2010.

Key focuses for this release are:
 * Parallel Extensions to improve support for parallel computing, which target multi-core or distributed systems. To this end, technologies like PLINQ (Parallel LINQ), a parallel implementation of the LINQ engine, and Task Parallel Library, which exposes parallel constructs via method calls, are included.
 * New Visual Basic .NET and C# language features, such as implicit line continuations, dynamic dispatch, named parameters, and optional parameters
 * Support for Code Contracts
 * Inclusion of new types to work with arbitrary-precision arithmetic (System.Numerics.BigInteger) and complex numbers (System.Numerics.Complex)
 * Introduced Common Language Runtime (CLR) 4.0

.NET Framework 4.0 is supported on Windows XP (with Service Pack 3), Windows Server 2003 (with Service Pack 2), Vista (with Service Pack 1 or higher), Server 2008, 7 and Server 2008 R2. Applications utilizing .NET Framework 4.0 will also run on computers with .NET Framework 4.5 or 4.6 installed, which supports additional operating systems. Support for .NET Framework 4.0 ended on 12 April 2016 and is no longer providing technical support, bug fixes, or security fixes for .NET Framework 4.0 vulnerabilities which may be subsequently reported or discovered. .NET Framework 4.0 is the last version to support Windows XP and Windows Server 2003.

Development
Microsoft announced the intention to ship .NET Framework 4 on 29 September 2008. The Public Beta was released on 20 May 2009.

On 28 July 2009, a second release of the .NET Framework 4 beta was made available with experimental software transactional memory support. This functionality is not available in the final version of the framework.

On 19 October 2009, Microsoft released Beta 2 of the .NET Framework 4. At the same time, Microsoft announced the expected launch date for .NET Framework 4 as 22 March 2010. This launch date was subsequently delayed to 12 April 2010.

On 10 February 2010, a release candidate was published: Version:RC.