Multi-monitor

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%.

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.

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).

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Wikipedia