In a network, a cross-bar switch is a device that is capable of channeling data between any two devices that are attached to it up to its maximum number of ports. The paths set up between devices can be fixed for some duration or changed when desired and each device-to-device path (going through the switch) is usually fixed for some period.
Cross-bar topology can be contrasted with bus topology, an arrangement in which there is only one path that all devices share. Traditionally, computers have been connected to storage devices with a large bus. A major advantage of cross-bar switching is that, as the traffic between any two devices increases, it does not affect traffic between other devices. In addition to offering more flexibility, a cross-bar switch environment offers greater scalability than a bus environment.