Windows Server 2008 R2 is a server operating system produced by Microsoft. It was released to manufacturing (RTM) on July 22, 2009 and launched on October 22, 2009. According to the Windows Server Team blog, the retail availability was September 14, 2009. It is built on Windows NT 6.1, the same kernel used with the client-oriented Windows 7. It is the first 64-bit-only operating system released from Microsoft. Version enhancements include new functionality for Active Directory, new virtualization and management features, version 7.5 of Microsoft IIS Web Server and support for up to 256 logical processors.