Windows Vista, abbreviated WinVI, is Microsoft's next version of its Windows operating system, succeeding to Windows XP. It was previously known by its codename Longhorn. See the Microsoft codenames list for the names of others. The name "Vista" was unveiled on July 22, 2005. Longhorn Server, the successor of Windows Server 2003, is yet to be named. Windows Vista will carry the version number 6.0 (Windows 2000, Windows XP and Windows Server 2003 being Windows NT versions 5.0, 5.1 and 5.2, respectively).