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 50–70%. Measurements of the Institute for Occupational Safety and Health of the German Social Accident Insurance showed that the quality and quantity of worker performance varies according to the screen setup and type of task. Overall, the results of physiological studies and the preferences of the test persons favour a dual-monitor rather than single-monitor setup. Physiologically limiting factors observed during work on dual monitors were minor and not generally significant. There is no evidence that office work with dual-monitor setups presents a possible hazard to workers. Implementation Multiple computers can be connected to provide a single display, e.g. over Gigabit Ethernet/Ethernet to drive a large video wall. Display modes USB One 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 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. In video gaming 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 monitors 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 addition