Wikipedia
A "powerwall" is a large, ultra-high-resolution display that is constructed of a matrix of other displays, which may be either monitors or projectors. It is important to differentiate between Powerwalls and displays that are just large, for example, the single projector display used in many lecture theatres. These displays rarely have a resolution higher than 1920x1080 pixels, and so present the same amount of information as on a standard desktop display. With Powerwall displays, users can view the display from a distance and see an overview of the data (context), but can also move to within arm’s length and see data in great detail (focus). This technique of moving around the display is known as physical navigation, and can help users to better understand their data.
The first Powerwall display was installed at the University of Minnesota in 1994. It was made of four rear-projection displays, providing a resolution of 7.8 million pixels (3200x2400 pixels). Increases in graphic display power, combined with decreases in hardware costs, means that less hardware is required to drive such displays. In 2006, a 50-60 mega-pixel Powerwall display required a cluster of seven machines to drive it, in 2012 the same display could be driven by a single machine with three graphics cards, and in 2015 it could be driven by a single graphics card alone. Rather than seeing a decrease in the use of PC clusters as a result of this, we are instead seeing cluster-driven Powerwall displays with even higher resolutions. Currently, the highest resolution display in the world is the Reality Deck, running at 1.5 billion pixels, powered by a cluster of 18 nodes.