Video devices are the part of computers that users are most familiar with. A computer's video card renders the current state of the computer into a user interface displayed on a monitor. Because users don't interact with clusters in the same way, video cards on clusters are typically used for visualization. That is, a graphical representation is developed for the purposes of user interaction. Most video or graphics devices are currently connected with AGP (see Section 2.4.2). Previous generations of graphics adapters were connected with PCI (see Section 2.4.1), but the PCI bus did not adequately provide bandwidth for video-intensive applications.
The main usage scenario for graphics adapters in clusters is the driving of tiled displays. Tiled displays are large installations wherein the output of multiple video cards are used in parallel to provide higher resolution than would be possible with a single device. These displays are generally used for displaying regions of 3D visualizations, so a graphics adapter's performance in this area is important. Many gaming web sites post reviews of current video adapters. As this is an area where new hardware is released from week to week, these sites are the sources of the best, up to date information. In most clusters, where visualizations are not displayed on local hardware, the particular graphics adapter present in a system is not important; it is most likely used to debug hardware problems and update BIOS settings.