Multi-monitor, also called multi-display and multi-head, is the use of multiple physical display devices, such as monitors, televisions, and projectors, in order to increase the area available for computer programs running on a single computer system. Research studies show that, depending on the type of work, multi-head may increase the productivity by up to 50-70%.
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Implementation
Support for a multi-monitor setup is either achieved by installing multiple graphics cards into one computer or by special display controllers, that have the ability to feed multiple monitors independently with a signal. Monitors supporting DisplayPort allow to drive multiple monitors from only one external clock. DisplayPort version 1.2 supports Multi-Stream Transport; this makes it possible to drive multiple displays on one single DisplayPort connector using a multi-head cable or loop through.
Furthermore, multiple computers can be connected to provide a single display, e.g. over Gigabit Ethernet/Ethernet to drive a large video wall.
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Display modes
Clone mode
Since before personal computers existed, video signals have been split with simple Y-adapters to provide duplicate signals to multiple monitors for various reasons. When personal computers came to have video outputs, this naturally carried over--sometimes for presentations, and sometimes to provide a different representation of the same output (for example color alongside the higher resolution monochrome interpretation of the output of an Apple II). Later systems - particularly portable machines with built-in displays -- provided built-in redundant outputs for this. Even later systems, in addition to being capable of the discrete modes described below, are able to mimic this "cloning" or "mirroring" behavior (typically defaulting to it upon power-up/reset).
Extended mode
Extended mode creates one virtual display with the resolution of all participating monitors. Depending on the employed hardware and software, the monitors must be driven all with the same resolution or each monitor can participate with a different resolution.
Both of these modes present the display space to the user as a contiguous area, allowing objects to be moved between, or even straddled across displays as if they are one.
Graphics devices
The biggest manufacturers of graphics card or on-board graphics products support multiple monitor configurations. This includes Nvidia, AMD, Matrox and Intel. Limiting factors are now the number of physical ports than can be supplied rather than the abilities of the devices themselves.
USB
Another way to extend the number of displays on one computer is to add displays via USB. Starting in 2006, DisplayLink released several chips for USB support on VGA/DVI/LVDS and other interfaces.
Adoption
In the office
Specialized application environments such as CAD, day trading of corporate stocks, and software development are increasingly using six or more monitors on one production system.
In many professions, including graphic design, architecture, communications, accounting, engineering and video editing, the idea of two or more monitors being driven from one machine is not a new one. While in the past, it has meant multiple graphics adapters and specialized software, it was common for engineers to have at least two, if not more, displays to enhance productivity.
Multi-display setups are also very common in investment banks, particularly in market making, where they allow the simultaneous display of several screens of prices as reference data, allowing the trader to keep an eye on the market. Setups of 6 displays (2×3: 2 rows of 3) are common on interest rate trading desks, which involve many numbers, while 8 displays (2×4: 2 rows of 4) are not uncommon. Financial multi-display setups may also incorporate Bloomberg Terminals, or these may be adjunct to the main display.
Now that multi-monitor setups are more budget-friendly, it is not uncommon to see a wide range of business professionals using multiple monitors to increase visual area. This advantage helps promote the concept of a paperless office by increasing the quantity of simultaneous media that can be viewed digitally, although the advantage of viewing two documents simultaneously is also feasible on many larger widescreen monitors.
Professional audio production
Digital audio workstation are known to rely on multi-monitor setups to increase the available area for the user interface.
In video gaming
Multi-monitor gaming/simulation is also becoming more common; however, the hardware expense can be a limiting factor.
Video games that support multi-monitor set-ups
Early versions of DOOM permitted a three-monitor display mode, using three networked machines to show left, right, and center views.
More recently, games have used multiple monitor to show a more absorbing interface to the player or to display game information . Various flight simulators can use these monitor setups to create an artificial cockpit with more realistic interfaces. Others such as Supreme Commander and World in Conflict can use an additional monitor for a large scale map of the battlefield.
A large number of older games support multi-monitor set-ups by treating the total screen space as effectively a single monitor to the game, a technique known as spanning. Many games without inherent multi-monitor support such as Guild Wars and World of Warcraft can also be made to run in multi-monitor set-ups, with this technique or in conjunction with additional of third party software A larger list of games that support dual/multi screen modes is available at WSGF.
Other uses
Older uses
From the mid-1980s through 1990s, a popular configuration for software developers was to employ a general-purpose VGA, EGA, or CGA display for managing the program under development and an independent monochrome Hercules or MDA card driving a second monitor for displaying debugging information. Many DOS debugging applications supported this configuation. It was possible to operate two display cards in this fashion, even with operating systems such as MS-DOS which did not support multi-monitor natively, because the Hercules and MDA cards used a different hardware memory address than conventional graphics cards and could operate concurrently without creating hardware conflicts. Modern hardware is not affected by the limitations of earlier systems like these when running modern operating systems, because the hardware and software are both designed such that the operating system can abstract the various hardware devices from each other and then manage them appropriately. The first Macintosh computer to support multiple monitors was the Macintosh II. The Macintosh SE/30, which had one slot in it, also supported a second monitor which could be color even though the main monitor was monochrome.
Interactive television sometimes coordinates the use of a television screen and a computer display.
Arcade machines
Arcade games were released in the 1980s and 1990s which used a multi-monitor configuration. The earliest of these is the game TX-1, a 1983 driving game developed by Tatsumi and published by Namco/Atari, which used a cockpit cabinet with 3 19" CRT monitors side-by-side to give a wide viewing area. Its successor, TX-1 V8, released in 1984, also used the same 3 monitor configuration. Tatsumi released Buggy Boy in 1985, in both cockpit 3 monitor and upright single monitor cabinets. Darius from 1986 used an upright cabinet which was around half as wide again than a standard arcade cabinet of the time. It used 3 14" FST (flatter squarer tube) monitors but in this case, 2 monitors were mounted on the left and right with the screens pointing upwards and one was mounted in a box at the centre rear of the cabinet, and using a two way mirror a seamless wide image was obtained. A similar effect was seen in Darius II, also known as Sagaia (which was also released in twin larger monitor format) and The Ninja Warriors. The original 1987 arcade version of Tecmo Bowl also used a dual-monitor setup. In 1990, Galaxian 3 used up to 16 projected screens.
As arcade technology entered the 1990s, larger cabinets were being built which in turn also housed larger monitors such as the 3 28" screen version of Namco's Ridge Racer from 1993. Although large screen technology such as CRT rear projection was beginning to be used more often, multi-monitor games were still occasionally released, such as Sega's F355 Challenge from 1999 which again used 3 28" monitors for the sit-down cockpit version. The most recent use of a multi-monitor setup in arcades occurred with Taito's Dariusburst: Another Chronicle game, released in Japan in December 2010 and worldwide the following year. It uses 2 32" LCD screens and an angled mirror to create a seamless widescreen effect.
Developing software for multiple monitor workstations
Ordinary software does not need special support for multiple screens even if it uses graphic accelerator. At the usual application level multihead is presented just as a single larger monitor spanning over all screens. However some special approaches may increase the multihead performance.
With multiple monitors present, each screen will have its own graphics buffer. One possible scenario for programming is to present to OpenGL or DirectX a continuous, virtual frame buffer in which the OS or graphics driver writes out to each individual buffer. With some graphics cards, its possible to enable a mode called "horizontal span" which accomplishes this. The OpenGL/DirectX programmer then renders to a very large frame buffer for output. In practice, and with recent cards, this mode is being phased out because it does not make very good use of GPU parallelism, and does not support arbitrary arrangements of monitors (they must all be horizontal). A more recent technique uses the wglShareLists feature of OpenGL to share data across multiple GPUs, and then render to each individual monitor's frame buffer.
In Android
Android supports an additional monitor as of version 4.2 but additional software is needed to multi-task/use both at once.
Source of the article : Wikipedia
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