Implementations
Historically, a crossbar switch consisted of metal bars associated with each input and output, together with some means of controlling movable contacts at each cross-point. In the later part of the 20th Century these literal crossbar switches declined and the term came to be used figuratively for rectangular array switches in general. Modern "crossbar switches" are usually implemented with semiconductor technology. An important emerging class of optical crossbars is being implemented with MEMS technology.
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