1. A crossbar which is operable to route data from any of a first number of input channels to any of a second number of output channels according to routing control information, each combination of an input channel and an output channel comprising one of a plurality of links, the crossbar comprising crossbar circuitry which is operable to route the data in a deterministic manner on each of the links thereby preserving a partial ordering represented by the routing control information, wherein events on different links are uncorrelated.