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The system under discussion is a 4-wire pulse amplitude modulation system in which each subscriber is permanently allocated to one of 30 time-separated 10-kc/s pulse channels. Groups of 30 subscribers are connected to multiplex highways constituting inlets to an interhighway switch. The electronic crosspoints are operated at channel times by ferrite stores; ferrite stores also control supervisory and register functions, and a wires store is used for semipermanent line information. Marking wires, which parallel the speed highways, are used to select free paths through the network.