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This paper describes a system using an electronic stored program processor and ferrite core data memories to implement the routing control functions of a common control crossbar telephone central office. Of central importance to the design is provision for the system to be applicable both for new installations and for expanding existing offices without obsoleting equipment already in service. Processor hardware characteristics and maintenance features are discussed along with interface circuits, inputoutput equipment, and relay adapters. Operation of the system for routing of calls through the network is explained. Modularity of the system is such that it can be economically configured to encompass a wide range of office sizes. Provisions for achieving this modularity are discussed. Reliability considerations and switchover philosophy are explained for the system which has internal redundancy with duplicated processors.