Microsoft has not announced a ship date for Windows Server 8, although roadmap documents released some time ago pegged it for 2012 (earning it the nickname of Windows Server 2012). A developer's preview of Windows Server 8, including Hyper-V, was made available during Microsoft's BUILD conference in Anaheim, Calif., in September.
Much more than a minor upgrade, Windows Server 8 brings many new features and functionality. The software is currently a Developer Preview release. This means Windows Server 8 isn't even available for beta testing yet.
Windows Server 8 is a much more significant release than Windows Server 2003 or Windows Server 2008. Both of those products were good, but they were mostly evolutionary. In Windows Server 8, Microsoft has taken a much bolder approach and is creating an OS that's by far the most innovative since Windows 2000 Server.