In computing, a windowing system (or window system) is software that manages separately different parts of display screens. It is a type of graphical user interface (GUI) which implements the

WIMP Wimp, WIMP, or Wimps may refer to: Science and technology * Weakly interacting massive particle, a hypothetical particle of dark matter * WIMP (computing), the "window, icon, menu, pointer" paradigm * WIMP (software bundle), the web stack of Windo ...

( windows,

icon An icon () is a religious work of art, most commonly a painting, in the cultures of the Eastern Orthodox, Oriental Orthodox, and Catholic churches. They are not simply artworks; "an icon is a sacred image used in religious devotion". The most c ...

menu In a restaurant, the menu is a list of food and beverages offered to customers and the prices. A menu may be à la carte – which presents a list of options from which customers choose – or table d'hôte, in which case a pre-established seque ...

s, pointer) paradigm for a

user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine fr ...

. Each currently running application is assigned a usually resizable and usually rectangular surface of the display to present its GUI to the user; these windows may overlap each other, as opposed to a tiling interface where they are not allowed to overlap. Usually a

window decoration In computing, a window is a graphical control element. It consists of a visual area containing some of the graphical user interface of the program it belongs to and is framed by a window decoration. It usually has a rectangular shape that can ...

is drawn around each window. The programming of both the window decoration and of available widgets inside of the window, which are graphical elements for direct user interaction, such as sliders, buttons, etc., is eased and simplified through the use of

widget toolkit A widget toolkit, widget library, GUI toolkit, or UX library is a library or a collection of libraries containing a set of graphical control elements (called ''widgets'') used to construct the graphical user interface (GUI) of programs. Most widge ...

Technical details

The main component of any windowing system is usually called the

display server In computing, a windowing system (or window system) is software that manages separately different parts of display screens. It is a type of graphical user interface (GUI) which implements the WIMP ( windows, icons, menus, pointer) paradigm ...

, although alternative denominations such as window server or compositor are also in use. Any application that runs and presents its GUI in a window, is a client of the display server. The display server and its clients communicate with each other over a

communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchron ...

, which is usually called display server protocol, the display server being the mediator between the clients and the user. It receives all the input from the

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learni ...

, that the kernel receives from all attached

input device In computing, an input device is a piece of equipment used to provide data and control signals to an information processing system, such as a computer or information appliance. Examples of input devices include keyboards, mouse, scanners, cameras ...

s, such as

keyboard Keyboard may refer to: Text input * Keyboard, part of a typewriter * Computer keyboard ** Keyboard layout, the software control of computer keyboards and their mapping ** Keyboard technology, computer keyboard hardware and firmware Music * Mu ...

, pointing devices, or touchscreen and transmits it to the correct client. The display server is also responsible for the output of the clients to the

computer monitor A computer monitor is an output device that displays information in pictorial or textual form. A discrete monitor comprises a visual display, support electronics, power supply, housing, electrical connectors, and external user controls. The d ...

. The output of sound is usually not managed by the display server, but the sound volume is usually handled through GUI applets and it is the display server who decides which applications are on top. A windowing system enables the computer user to work with several programs at the same time. Each program presents its GUI in its own window, which is generally a rectangular area of the screen. From a

programmer A computer programmer, sometimes referred to as a software developer, a software engineer, a programmer or a coder, is a person who creates computer programs — often for larger computer software. A programmer is someone who writes/creates ...

's point of view, a windowing system implements graphical primitives. For example: rendering

fonts In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design. In mode ...

or drawing a line on the screen. It provides an abstraction of the graphics hardware for use by higher-level elements of the graphical interface such as a window manager. A display server protocol can be network capable or even network transparent, facilitating the implementation of thin clients.

Display server

Schema of the layers of the graphical user interface

A display server or window server is a program whose primary task is to coordinate the input and output of its clients to and from the rest of the operating system, the hardware, and each other. The display server communicates with its clients over the display server protocol, a

, which can be network-transparent or simply network-capable. The display server is a key component in any graphical user interface, specifically the windowing system.

Display server communications protocols

X11

One example of a display server is the

X.Org Server X.Org Server is the free and open-source implementation of the X Window System display server stewarded by the X.Org Foundation. Implementations of the client-side X Window System protocol exist in the form of ''X11 libraries'', which serve ...

, which runs on top of the kernel (usually a Unix-like kernel, such as Linux or

BSD The Berkeley Software Distribution or Berkeley Standard Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berke ...

). It receives user input data (e.g. from

evdev evdev (short for 'event device') is a generic input event interface in the Linux kernel and FreeBSD. It generalizes raw input events from device drivers and makes them available through character devices in the /dev/input/ directory. The user-s ...

on Linux) and passes it to one of its clients. The display server also receives data from its clients; it processes the data, it does the compositing and on Linux it passes the data to one of three kernel components –

DRM DRM may refer to: Government, military and politics * Defense reform movement, U.S. campaign inspired by Col. John Boyd * Democratic Republic of Madagascar, a former socialist state (1975–1992) on Madagascar * Direction du renseignement milita ...

gem A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, an ...

KMS driver The Direct Rendering Manager (DRM) is a subsystem of the Linux kernel responsible for interfacing with GPUs of modern video cards. DRM exposes an API that user-space programs can use to send commands and data to the GPU and perform operations ...

. The component writes the data into the framebuffer and content of the framebuffer is transmitted to the connected screen and displayed. X relies on

GLX GLX (initialism for "OpenGL Extension to the X Window System") is an extension to the X Window System core protocol providing an interface between OpenGL and the X Window System as well as extensions to OpenGL itself. It enables programs wishi ...

. One of the implementations of display server concept is

X Window System The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wi ...

, in particular its actually used version –

and

Xlib Xlib (also known as libX11) is an X Window System protocol client library written in the C programming language. It contains functions for interacting with an X server. These functions allow programmers to write programs without knowing the d ...

and

XCB XCB (''X protocol C-language Binding'') is a library implementing the client-side of the X11 display server protocol. XCB is written in the C programming language and distributed under the MIT License. The project was started in 2001 by ...

client libraries. The X.Org Server is a display server, but in its current implementation it relies on a second program, the

compositing window manager A compositing window manager, or compositor, is a window manager that provides applications with an off-screen data buffer, buffer for each window. The window manager Compositing, composites the window buffers into an image representing the screen ...

, to do the compositing. Examples are Mutter or

KWin KWin is a window manager for the X Window System and a Wayland compositor. It is released as a part of KDE Plasma 5, for which it is the default window manager. KWin can also be used on its own or with other desktop environments. KWin can be ...

. Notable examples of display servers implementing the X11 display server protocol are

, XFree86,

XQuartz XQuartz is an open-source version of the X.Org X server, a component of the X Window System (X11, or shortened to simply X, and sometimes informally X-Windows) that runs on macOS. It formally replaced Apple's internal X11 app. The name "XQuart ...

and Cygwin/X, while client libraries implementing the X11 display server protocol are

and

Wayland

Display servers that implement the Wayland display server protocol are called

Wayland compositor Wayland is a communication protocol that specifies the communication between a display server and its clients, as well as a C library implementation of that protocol. A display server using the Wayland protocol is called a '' Wayland compositor ...

s. Like any display server, a Wayland compositor is responsible for handling input and output for its clients and – in contrast to X11 – additionally for the

compositing Compositing is the process or technique of combining visual elements from separate sources into single images, often to create the illusion that all those elements are parts of the same scene. Live-action shooting for compositing is variously ca ...

. Examples are

Weston Weston may refer to: Places Australia * Weston, Australian Capital Territory, a suburb of Canberra * Weston, New South Wales * Weston Creek, a residential district of Canberra * Weston Park, Canberra, a park Canada * Weston, Nova Scotia ...

, Mutter,

or Enlightenment. Wayland compositors communicate with Wayland clients over the

Wayland display server protocol Wayland may refer to: Computers * Wayland (display server protocol), a graphical display system for Unix-like computers Fiction * Jace Wayland, a character in the ''Mortal Instruments'' book series * Wayland (''Star Wars''), a planet in the '' ...

. This protocol defines that clients can directly write data into the framebuffer using the EGL rendering API. The display server still gets to decide which window is on top and thus visible to the user and also still is responsible for passing data regarding to input devices from

to its clients. Wayland is used to a certain degree in some Linux desktop distributions, such as

Fedora A fedora () is a hat with a soft brim and indented crown.Kilgour, Ruth Edwards (1958). ''A Pageant of Hats Ancient and Modern''. R. M. McBride Company. It is typically creased lengthwise down the crown and "pinched" near the front on both sides ...

. It is also well suited for mobile computing and has been adopted, for example, by the smartphone- and tablet-focused projects Tizen,

Sailfish OS Sailfish OS is a Linux-based operating system based on free software, and open source projects such as Mer as well as including a closed source UI. The project is being developed by the Finnish company Jolla. The OS first shipped with the ...

and

AsteroidOS AsteroidOS is an open source operating system designed for smartwatches. It is available as a firmware replacement for some Android Wear devices. The motto for the AsteroidOS project is "Hack your wrist." Wareable.com reviewed version 1.0 and ga ...

. An implementation of Wayland is available under the MIT License, the libwayland-client and libwayland-server libraries. There is an ongoing effort to add Wayland support to

ChromeOS ChromeOS, sometimes stylized as chromeOS and formerly styled as Chrome OS, is a Linux-based operating system designed by Google. It is derived from the open-source ChromiumOS and uses the Google Chrome web browser as its principal user interfac ...

Mir

The Mir display server comes with its own Mir display server protocol which is different from those used by X11 and Wayland. Mir additionally supports the X11 protocol. It was developed by

Canonical The adjective canonical is applied in many contexts to mean "according to the canon" the standard, rule or primary source that is accepted as authoritative for the body of knowledge or literature in that context. In mathematics, "canonical exampl ...

and was intended to be the display server of choice for

Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: '' Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All the ...

. As of 2017, it has been replaced with the Wayland display server for desktop editions of Ubuntu. There are implementations of the Mir display server, the libmir-server and the libmir-client libraries available under the

GPLv3 The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general u ...

SurfaceFlinger

Google developed a display server called SurfaceFlinger for Android (another Linux kernel-based operating system primarily for mobile devices): Everything in Android is rendered to a "surface"; "surfaces" are produced by applications and placed into a queue that is managed by SurfaceFlinger. Yet another Android-specific solution is "Gralloc". Gralloc handles device memory i.e. it does allocation, arbitration, it handles synchronization via Android/Linux fence file descriptors. Gralloc competes with other solutions like e.g. Mesa's

Generic Buffer Management Mesa, also called Mesa3D and The Mesa 3D Graphics Library, is an open-source software, open source implementation of OpenGL, Vulkan, and other computer graphics, graphics Application programming interface, API specifications. Mesa translates the ...

(GBM) or Nvidia's EGLStreams. The Gralloc hardware abstraction layer (HAL) is used to allocate the buffers that underlie "surfaces". For compositing in Android, Surfaces are sent to SurfaceFlinger, which uses OpenGL ES to do the compositing. Hardware Composer HAL (HWC) was introduced in Android 3.0 and has evolved steadily over the years. Its primary purpose is to determine the most efficient way to composite buffers with the available hardware. As a HAL, its implementation is device-specific and usually done by the display hardware OEM.

Quartz Compositor

For Apple's macOS family of operating systems,

Quartz Compositor Quartz Compositor is the display server (and at the same time the compositing window manager) in macOS. It is responsible for presenting and maintaining rasterized, rendered graphics from the rest of the Core Graphics framework and other rend ...

fulfils the tasks of a display server and of a window manager in the windowing system.

Desktop Window Manager

For Microsoft Windows, from Windows Vista onward,

Desktop Window Manager Desktop Window Manager (DWM, previously Desktop Compositing Engine or DCE) is the compositing window manager in Microsoft Windows since Windows Vista that enables the use of hardware acceleration to render the graphical user interface of Windows ...

enables the use of hardware acceleration to render the graphical user interface. It was originally created to enable portions of the new "Windows Aero" user experience, which allowed for effects such as transparency, 3D window switching and more. It is also included with Windows Server 2008, but requires the "Desktop Experience" feature and compatible graphics drivers to be installed. From Windows 8 onwards DWM can't be disabled and is software rendered if no suitable graphics card is installed.

List of windowing systems

For Unix-like operating systems

8½ ' (Italian title: , ) is a 1963 surrealist comedy-drama film directed and co-written (with Tullio Pinelli, Ennio Flaiano and Brunello Rondi) by Italian filmmaker Federico Fellini. The metafictional narrative centers on Guido Anselmi, played by ...

and

rio Rio or Río is the Portuguese, Spanish, Italian, and Maltese word for "river". When spoken on its own, the word often means Rio de Janeiro, a major city in Brazil. Rio or Río may also refer to: Geography Brazil * Rio de Janeiro * Rio do Sul, a ...

for Plan 9 * FramebufferUI in-kernel windowing system * ''HP Windows/9000'' (on early versions of HP-UX) * Sapphire for the PERQ *

ManaGeR Management (or managing) is the administration of an organization, whether it is a business, a nonprofit organization, or a government body. It is the art and science of managing resources of the business. Management includes the activities o ...

(MGR) *

Metisse Metisse is a 2.5D X window manager with many features that set it apart from the traditional 3D "cube" workspace. Windows can be turned three-dimensionally in any direction, enabling the user to fit more windows onto a screen, and they can be sc ...

Mir ''Mir'' (russian: Мир, ; ) was a space station that operated in low Earth orbit from 1986 to 2001, operated by the Soviet Union and later by Russia. ''Mir'' was the first modular space station and was assembled in orbit from 1986 to& ...

* NeWS /

OpenWindows OpenWindows is a discontinued desktop environment for Sun Microsystems workstations which combined SunView, NeWS, and X Window System protocols. OpenWindows was included in later releases of the SunOS 4 and Solaris operating systems, until its r ...

* NeXT DPS * Orbital ( Redox) *

Qt Extended Qt Extended (named Qtopia before September 30, 2008) is an application platform for embedded Linux-based mobile computing devices such as personal digital assistants, video projectors and mobile phones. It was initially developed by Qt Software, ...

( Mac OS X) *

SunView SunView (Sun Visual Integrated Environment for Workstations, originally SunTools) is a discontinued windowing system from Sun Microsystems developed in the early 1980s. It was included as part of SunOS, Sun's UNIX implementation; unlike lat ...

* Twin (Text WINdows) * W Window System * Wayland *

XFast XFast is a lightweight desktop environment that incorporates a display manager and a window manager within the same process. It is portable and works on many devices (embedded devices, handhelds, set-top boxes,...). Here the communication betwee ...

Xynth Xynth is an embedded windowing system, released under LGPL, developed for systems with low resources, is an alternative for X Window System. The goal of the project is to release a soft but portable and powered Window Environment. The source lan ...

For Windows NT-family operating systems

(DWM) in Microsoft Windows ( Vista and later) * ReactOS Explorer *

Classic Shell Classic Shell is a computer program for Microsoft Windows that provides user interface elements intended to restore familiar features from past versions of Windows. It focuses on the Start menu, File Explorer and Internet Explorer — three maj ...

* Pokki * RetroUI *

Talisman Desktop Talisman Desktop is a Windows shell replacement introduced in 1997 by Lighttek Software, designed to allow the user to configure its interface. It is available in a number of languages including English, French, Spanish, Swedish, Portuguese, Russi ...

Web Web most often refers to: * Spider web, a silken structure created by the animal * World Wide Web or the Web, an Internet-based hypertext system Web, WEB, or the Web may also refer to: Computing * WEB, a literate programming system created by ...
windowing systems

* Dojo *

ExtJS Ext JS is a JavaScript application framework for building interactive cross-platform web applications using techniques such as Ajax, DHTML and DOM scripting. It can be used as a simple component framework (for example, to create dynamic grids on ...

* TIBCO General Interface * Web Window Manager

Other

* DM *

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Intuition Intuition is the ability to acquire knowledge without recourse to conscious reasoning. Different fields use the word "intuition" in very different ways, including but not limited to: direct access to unconscious knowledge; unconscious cognition; ...

* Microwindows * MiniGUI * OOHG * Visi On * VWS (VAX Workstation Software) Some systems such as Microsoft Windows ( XP, 9x and earlier), the

classic Mac OS Mac OS (originally System Software; retronym: Classic Mac OS) is the series of operating systems developed for the Macintosh family of personal computers by Apple Computer from 1984 to 2001, starting with System 1 and ending with Mac OS 9. Th ...

(version 9 and earlier), and

Palm OS Palm OS (also known as Garnet OS) was a mobile operating system initially developed by Palm, Inc., for personal digital assistants (PDAs) in 1996. Palm OS was designed for ease of use with a touchscreen-based graphical user interface. It is provi ...

, contain a windowing system which is integrated with the OS.

References

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