Fast user switching is a feature on some moern multi-user operating systems such as Windows XP, Windows Vista, Mac OS X, OpenSUSE, Ubuntu and Fedora. It allows users to switch between user accounts on a single PC without quitting applications and logging out. Analogous functionality was first developed on consumer level hardware by the Xenix operating system which supported multiple virtual consoles. Linux, BSD, and most other PC Unixes adopted virtual terminals and further developed the user interfaces, including allowing users to optionally run separate graphical X Window System sessions.