Dual Head Video Cards

Multi-monitor , also called Multi-display , Multi-head , 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 multiple monitors. Dual 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 video card that supports two discrete outputs is referred to as Dual Head. Two separate video cards are just as acceptable, and so is using an integrated motherboard video socket plus a second video card, provided the integrated graphics are not automatically disabled by the installation of the peripheral card (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.

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

Multiple PC multi-monitor

Using 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.

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.

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 mode

Alternatively, some video cards are able to "span" the existing desktop area across two monitors rather than create additional desktop space. This is accomplished by using a resolution such as 2048x768, with each monitor at a resolution of 1024x768. Both monitors need to have the same color depth settings, and often the same refresh rate. Differing resolutions may result in some screen space not being assigned to either monitor.

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.

Extended mode

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.

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 DualHead 2Go and TripleHead 2Go . 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 dual 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 unavailab

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Re: Recomended dual head video card

On Thursday 07 October 2004 15:42, Bill Carlson wrote: >I run a G450 dual head, be warned there is a problem with gamma >correction on the second head.

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Dual head video card questions System Hardware ... Hi all, Hopefully this post isnt too much of a mess, but I can only work from my phone until I get my DSL here, didn't have any ...

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Re: Recomended dual head video card

On Tue, 5 Oct 2004 14:44:49 +0900, Nick Hastings wrote: >>Hi all, >>for reasons I won't bother going into I'm about turn a server >machine into a ...

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using the dual-head functionality on two separate video cards | Gas ...

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Re: Dual Head Video Cards

From: Guy Fraser To: For users of Fedora Core releases Subject: Re: Dual Head Video Cards; Date: Wed, 13 Oct 2004 13:48:42 -0600

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Dual-Head Video Cards? : Windows Hardware & Software

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RE: Dual head AGP video card recommendations

From: "Chris Manning" To: "'For users of Fedora Core releases'" Subject: RE: Dual head AGP video card recommendations

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Re: Dual Head Video Cards

From: Graham Leggett To: For users of Fedora Core releases Subject: Re: Dual Head Video Cards; Date: Wed, 13 Oct 2004 20:36:12 +0200

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