It was a well-known information Microsoft will deliver its new virtualization platform, Windows Server Virtualization (WSV or codename Viridian), 180 days after Windows Server 2008 (formerly codename Longhorn) RTM. It was also known the new hypervisor will appear as new server role among ones available in the Server Core edition of Windows, a thin version of the operating system with just kernel and few subsystems on top (and GUI will not be one of them).
What was unknown is the delivery method to be used to distribute Vidirian inside Windows Server 2008. At WinHEC 2007 Microsoft clarified the new hypervisor will come through Windows Update, as reported by Bink.nu.