http://en.wikipedia.org/wiki/Windows_Server_2008#Windows_Server_2008_R2 said:
Microsoft introduced Windows Server 2008 R2 at the 2008 Professional Developers Conference as the server variant of Windows 7. A reviewer guide published by the company describes several areas of improvement,[22] notably the inclusion of a number of new virtualization capabilities, reduced power consumption, a new set of management tools, new Active Directory capabilities such as a "recycle bin" for deleted AD objects, a new FTP server, DNSSEC support, and an increase in the number of supported processing cores from 64 to 256. 32-bit processors are no longer supported.