The X Window System (commonly X or X11) is a computer software system and network protocol that provides a graphical user interface (GUI) for networked computers. It implements the X display protocol (invented by Hewlett Packard)[citation needed] and provides windowing on raster graphics (bitmap) computer displays and manages keyboard and pointing device control functions. In its standard distribution, it is a complete, albeit simple, display and human interface solution, but also delivers a standard toolkit and protocol stack for building graphical user interfaces on most Unix-like operating systems and OpenVMS, and has been ported to many other contemporary general purpose operating systems. Most modern GUIs developed for Linux and other UNIX-like systems, such as GNOME, KDE, and Xfce, use the X Window System as a foundation.
X provides the basic framework, or primitives, for building such GUI environments: drawing and moving windows on the screen and interacting with a mouse and/or keyboard. X does not mandate the user interface — individual client programs handle this. As such, the visual styling of X-based environments varies greatly; different programs may present radically different interfaces. X is built as an additional application layer on top of the operating system kernel.
Unlike previous display protocols, X was specifically designed to be used over network connections rather than on an integral or attached display device. X features network transparency: the machine where an application program (the client application) runs can differ from the user's local machine (the display server).
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