The iPSC/Z communications module usesa Direct-Connectctm) routing module (DCM) on each node. The DCMs connect the hypercube backplane wires, creating a circuit switched network and also provide the interface between the network and the node processors. The important improvements that are provided by the DCM technology include hardware routing decisions, elimination of store and forward protocol, unlimited message length, bi-directional message traffic, concurrent
message paths within the router and a boost in bandwidth to 2.8 Mbytes/set in each direction. The full duplex bandwidth is ten times the bandwidth of the iPSC/l. The target latency (time it takes to send a zero byte message between two nodes) is set at 350 microseconds (the examples quoted in this paper were run with the beta release software which had a latency of 490 microseconds). This represents an improvement in latency over the iPSC/l of a factor of three for nearest nei hbor communications and up to a factor of twenty for multihop messages. The total % enefit of the DCM routing in the iPSC/2 can combine to give as much as 30 times the performance of the iPSC/l.