These release notes address the most critical issues and information about the Windows Server 2012 R2 or Windows 8.1 operating systems (two separate document files). For information about by-design changes, new features, and fixes in this release, see documentation and announcements from the specific feature teams. For information about important steps to take before installing this release, including issues that you may need to work around, see “System Requirements and Installation Options for Windows Server 2012 R2 Preview.” Unless otherwise specified, these notes apply to all editions and installation options of Windows Server 2012 R2 or Windows 8.1, respectively.
http://www.microsoft.com/en-us/download/details.aspx?id=40244