Windows Server 2008 R2 is an operating system from Microsoft. It is an update of Windows Server 2008. Unlike Server 2003 R2, this R2 is a fully new Operating System. It is only available in 64-bit versions.
Windows Server 2008 R2 is a significantly updated version of Windows Server 2008. Unlike Server 2008, 2008 R2 is only available in 64-bit versions. No 32-bit version exists. It is superseded by Windows Server 2012