Include all updates till October-2011. 64bit only.

Microsoft introduced Windows Server 2008 R2 at the 2008 Professional Developers Conference as the server variant of Windows 7. Enhancements include new functionality for Active Directory, new virtualization and management features, version 7.5 of the Internet Information Services web server and support for up to 256 logical processors. It is built on the same kernel used with the client-oriented Windows 7, and is the first 64-bit only operating system released from Microsoft.

http://www.microsoft.com/windowsserver2008/en/us/default.aspx.