Multi-monitor

Multi-Monitor, also called Multi-Display, Multi-Head, Dual-Display, and Dual-Monitor, 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. Microsoft describes this setup as "one of the best ways to improve your productivity". Randy Pausch recommended multiple monitors for improving personal productivity in his Time Management lecture.

History

Contemporary versions of Microsoft Windows, Mac OS, and X Window System (used by GNU/Linux) all support simultaneous use of multiple monitors. Multi-monitor support once depended on specialized proprietary video drivers supplied with few video cards, along with a multi-display-supporting GUI system. Support for multiple monitor configurations was added as a standard feature in Microsoft Windows in Windows 98. It has been a standard feature in all versions of Apple's Mac OS X (introduced in March 2001), and was a standard feature of the first color Macintosh II introduced in 1987.

By adding up to two additional video cards, the Mac supported up to three monitors, although operating system support for multiple monitors wasn't introduced in Windows until the mid 1990s. The all-in-one Mac SE/30 featured a small black & white screen, but could drive an external color monitor.

Configuration and placement

In a multi-monitor configuration, an optimal layout is for each screen to be facing the viewer at the same distance.

Single PC multi-monitor

A multiple monitor setup increases the net display area of a system and can be an inexpensive way of improving computer usage. Resulting display area after upgrading to a multi-monitor configuration is limited by the size, resolution and number of monitors. The monitors used for multi-monitor can be different types (LCD or CRT) and sizes. The operating system manages the monitors' resolutions independently.

Video output on a computer is generated by a video graphics device, typically on a removable card but which may also be integrated into the motherboard as a discrete device or as part of the chipset logic. The output is interpreted and displayed by a variety of devices. Video outputs are generally connected to a monitor (of either the CRT or LCD type), however they are increasingly being connected to projection equipment or television sets. As a result of this trend, manufacturers have produced video cards which can connect to several types of display devices using the appropriate interface. A "Dual Head" configuration utilizes a video card that supports two discrete outputs. Users may also utilize two discrete video cards, and sometimes even an integrated motherboard video socket plus a second video card, though often the motherboard disables the integrated video when a discrete video card is used (a limitation that was common on older chipsets featuring integrated AGP graphics and an AGP upgrade slot).

More than two monitors

Prior to mainstream adoption of the PCIe bus, configurations of more than two monitors were either achieved with an AGP card with dual video outputs or by using an AGP graphics adapter as the primary device and a Conventional PCI graphics adapter as a secondary device. Given the bandwidth limitations of the older PCI bus, however, such setups were not common, and maximum overall graphics performance could be obtained only by using specialty solutions such as the Matrox G450, which features four outputs from one graphics adapter. Now that computers with two or more PCIe interfaces are popular, middle- and high-end computers are no longer limited to two monitors driven by a single main graphics adapter. If a dual PCIe interface is not available or is otherwise occupied, a standard PCI graphics card can still be used to provide additional video outputs, albeit with performance trade-offs. 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.

A Quad Monitor Digital Audio Workstation

Additional monitors can also be connected to PCs via a USB connection such as DisplayLink.

Multiple PC multi-monitor

Software such as Maxivista for Windows and ScreenRecycler for Mac OS X let you set up multiple PC multi-monitor mode through virtual display drivers and client-side software. Similarly, software such as InputDirector or Synergy allows one to use multiple PCs, each with their own monitor or monitors, and transition from one to the other on screen edges as if they were one machine. This allows each machine to be doing a different task, freeing up resources.

Linux users may use Xdmx, which is an X Window proxy. It is possible to have multiple monitors displaying as a single virtual desktop. Multiple university display wall projects use this capability, such as The LambdaVision display by the University of Illinois at Chicago's Electronic Visualization Laboratory, with 55 LCD monitors which are connected to 32 PCs. This results in a 17600 x 6000 pixel display. As long as the xinerama extension is enabled, GNOME can use the entire desktop.

An additional and different approach to multiple monitor systems involves using the monitors of networked computers to display the output of a central computer. By using the graphic cards of the networked computers, stability and speed are dramatically enhanced. This is often a preferred choice for systems in which adding additional graphics cards is problematic, such as laptops.

The additional monitors can be extensions of the desktop or mirrors of the central display. The arrangement of these monitors can be configured within the properties tab in the windows display dialog box, making horizontal, vertical, or other monitor configurations possible. Further, because the additional monitors are powered by networked computers, they can be located wherever the network reaches, both wireless and hardwired.

Display modes

Clone mode

Initially on PCs, the multiple output interface was designed to display the same image on all output interfaces (sometimes referred to as mirroring or cloning). This reflected the original use of these video cards in presentations where the user typically faced the audience and saw a duplicate of the projected image. Other modes have since become available.

Span or extended desktop mode

Some video cards are able to "span" the existing desktop area across two monitors rather than create additional desktop space. This is accomplished by doubling either the horizontal or vertical resolution. For example, when two 1024x768 displays are used, they could have a virtual resolution of either 2048x768 or 1024x1536. Both monitors may need to have the same color depth settings and refresh rate. When screen resolution or monitor placement within the virtual desktop is mismatched, the physical displays will not show all of the virtual desktop.

In "extended" mode, additional desktop area is created on additional monitors. Each monitor can use different settings (resolution, color, refresh rate). For example, a projector can show a presentation while the operator sees an advanced view of all slides. Macintosh computers have supported the "extended desktop" concept since the late 1980s, increasing the platform's utility for professional media and software developers such as graphic designers, video editors, and game developers.

The concept was further developed by PC manufacturers and led to the "extended" or "independent displays" mode and the "spanning" or "stretched" display mode. In both of these modes, display devices are positioned next to each other in order to create the illusion that the two displays are logically contiguous.

Hybrid Span mode

This is a technique that allows using multiple GPUs to create one single unified display. This is a driver feature which can overcome the 10 monitor limit in current Microsoft operating systems.

Commercial systems

Major players in the visual computing technologies currently include ATI Technologies (now a division of AMD), which supplies graphics hardware and supports its function via ATI's Hydravision Multi-Monitor Management Software; NVIDIA, also a hardware supplier, which includes software support under the moniker of nView Multi-Display Technology; and Matrox, a third hardware supplier providing both multi-display add-in boards and a series of external multi-display upgrade units known as DualHead2Go and TripleHead2Go. The technology provided by these companies was once limited to the professional graphics market, but has gradually become more widespread and affordable in the consumer market. The latest version of Microsoft Windows supports up to 64 monitors.

Disadvantages

The primary hardware disadvantage to multi-monitor use is that common resources of the video card are divided between each display's output duties. For example, if a user is showing a 2D widescreen desktop display at 1680x1050 resolution and 32-bit color depth on a second monitor while playing a game on the primary monitor, nearly 7MB of video memory (VRAM) will be consumed by the second display image, making it unavailable to the game. In some cases, the decreased processing power and VRAM available to each display may lead to unacceptable performance on both devices. When this situation is encountered, the common remedy is to install an additional video adapter and connect the additional display to the new device. Ongoing improvements in graphics technology have minimized this issue in recent years, with many mainstream graphics adapters now supporting 512MB or more of VRAM and a graphics core purpose-built around two or more video outputs.

Although multi-monitor configurations are increasing in number, single monitor PC users continue to dominate the market. Cost can be one problem for multi-monitor, as there is the cost of the second display and sometimes an additional video adapter as well. Furthermore, growth in 16:9 and 16:10 aspect ratio wide-screen LCD technologies has led to decreased cost for larger, wider displays, and some users may find that multi monitor does not add significant utility over a similarly-priced widescreen display.

Full-screen software can pose a problem on a multi-monitor configuration. Many full-screen applications make use of the absolute edge of the display to control view movement, and may not work properly on a multi-monitor PC, for example by failing to track the mouse cursor properly when it continues onto the next display of an extended desktop. "Edge-scrolling" can frequently be found in full-screen image viewers, 3D model editors, and RTS (RealTime Strategy) genre video games. Newer software is more likely to either be multi-monitor aware, or else not depend on the endpoints of the visual area as a fixed reference, albeit this does not solve all of the ergonomic problems a user may encounter.

For example, many full-screen applications, even when tolerant of multi-monitor displays, only cover one display area and relegate the other display to secondary use. This can create edge-scrolling problems when the cursor crosses between the display fields. One notable exception includes flight simulator software, which might take over all available displays, e.g. using one display to show a windshield view of the simulated flight and presenting simulated instrumentation and controls on another display.

Problems can also arise if the user clicks outside of the full-screen application's display area. Clicking in another display has a similar effect to hitting the Windows key or Alt-Tab, causing the desktop or another application to gain focus. The full-screen application loses focus, and may or may not pause any ongoing events in that application, depending on how the software is written.

When software is not multi-monitor aware, or the edge-scrolling problem is encountered, the user must adjust his or her computer usage to minimize it, or engage a work-around solution. One of the most common methods of overcoming the edge-scrolling problem is to set up a multi-monitor orientation on a diagonal. The diagonal orientation means there is no adjacent desktop space on any primary edge, generally preventing the mouse cursor from moving beyond the screen edge. As a downside, a diagonal orientation can make moving the mouse from monitor to monitor difficult, as the user must target a very narrow transition region in order to move the cursor between displays. A diagonal orientation also does not usually correspond to the physical arrangement of monitors, reducing the intuitiveness of the crossover point.

Another method is to temporarily disconnect the unused monitor(s). However it is not always desirable to disable all other displays, and on a Windows operating system platform, the OS will generally compensate for missing displays by reorganizing all desktop shortcuts onto the remaining active monitor(s). This can be overcome by using utilities that can store shortcut locations, such as ATT.

There are also some programs that provide full workarounds to the issue. One such utility is CSMMT.

Graphics cards

These display adapters are built with two or more outputs of various types. Typically these will be DVI ports and/or VGA. The older CRT monitors will usually use VGA, while higher-end CRTs may include BNC or DVI. LCDs - depending on the model - usually support either or both. Conventional or high-definition television outputs are also sometimes provided, although these will commonly disable one of the other display outputs when accessed and cannot be used to create a third display device.

Multi-display setups in the workplace

Office Worker with Dual Monitors

In many professions, including graphic design, architecture, communications, 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.

2×3 display setups are common in financial market making.

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 unknown. 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.

Programming

Programming multiple monitors is challenging because 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.

Available software

For a multiple monitor set-up, there is some software available.

• MurGeeMon (with tons of features and is cheap)
• Multimon (free version available)
• UltraMon
• Virtual Desktop manager
• DisplayFusion
• Monman (buggy)
• Actual Window Manager
• Actual Multiple Monitors (lesser version of previous - only multi-monitor functions)

Other uses

Older uses

At one time(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. 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. 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.

Multi-monitor support

• OS
  • Microsoft (not official): Virtual Display Manager
  • X Window: Xinerama and XRandR 1.2
  • Nvidia: nView (Windows) / TwinView (FreeBSD, Linux)
  • ATI: Hydravision, Eyefinity
  • Citrix Presentation Server (Citrix ICA Client)
  • Microsoft Terminal Services (RDP Client) value: RemoteApp
  • Multi Display QuadStations -2-12 Displays

Application support

• Adobe Photoshop Lightroom 2 can have images open on different displays and different viewing styles.
• Bloomberg Terminals use two or four monitors.
• Microsoft Office applications that do not employ the ribbon interface can have the toolbars moved to the second monitor. Some side panels can be moved to another screen even in recent versions.
• Microsoft Visual Studio 2010 supports multi-monitors, with support for multiple document windows and floating tool windows.
• Windows 7 introduces improved support for multiple monitors as compared to past releases of Microsoft Windows.

Games support

• Clear the Swarm is the first web game officially supporting multiple monitors.
• Microsoft Flight Simulator 2000
• Supreme Commander and World in Conflict (DX10 in multiplayer) both support multi-monitors in a dynamic manner of effectively displaying two aspects of the game simultaneously.
• Uplink (PC) features a multi-monitor option that utilizes the screens of two networked computers.
• Early versions of DOOM (1.0 and 1.1) permitted a three-monitor display mode, using three networked machines to show left, right, and center views.
• X²: The Threat (PC) often cited as one of the first video games to utilize a multiple monitor setup.
• Burnout Paradise the Ultimate Box for PC multi-monitor support can be accessed through the BurnoutConfigTool.exe in the directory where Burnout Paradise is located.
• DiRT 2

(Other games such as World of Warcraft and Team Fortress 2 can also be made to run in multi-monitor set-ups, with the addition of third party software to enable the ability.)

See also

• Multiseat configuration
• UltraMon
• Two-screen solutions
• Video wall
• Xinerama