"xscreen" refers to the graphical context for a display image. Although initially xscreen and display were synonymous - there being one display (device) per xscreen - nowadays the image defined by an xscreen can be displayed across a number of CRTs or LCD panels, each of which may be (erronously) referred to as a display, (instead of a display device). Thus the single image can be "stretched" across any number of display devices to make the displayed image associated with a single xscreen very large.

When an xscreen is divided between or among more than one display device, it may be referred to as a "stretched desktop," "Xinerama," "multi-view" or "single logical screen" display. In Summit, we usually refer to this display method as SingleLogicalScreen, or "SLS".

Many graphics cards with a single graphics chip have "back-end" hardware that allows more than one display to be driven by the card. A card with two display "channels," or paths, for example, can be set up to have each channel display a different half of the contents of the FrameBuffer that contains the image associated with an xscreen. Because the entire image is contained in a single FrameBuffer that is serviced by two output channels on the card, "stretching" the image across two displays is painless from a graphics driver point of view, and SLS is basically available by default. This is also true if the card has the ability to drive three or even four display devices from a single chip/FrameBuffer. All monitor views are hardware accelerated in Summit Series.

A system with a single graphics card with multiple graphics chips and output channels - or a system with multiple cards - requires a bit more software work to stretch a single xscreen across multiple displays that are serviced by different FrameBuffers. A "simple" case of a single card with four graphics chips each serviced by its own single output channel is the Matrox G450MMS. To make the four chips (FrameBuffers) work together to produce one xscreen covering four monitors is non-trivial and is only available in Summit in the WallDisplay (HX) series. For a more complete treatment of SLS in Summit, see the (13MB PDF) Intro to SLS.