Abstract: A private automatic branch telephone exchange system which includes an integral system for maintaining and updating selected data information. Interconnections between subscriber lines and trunk lines are accomplished with a unique non-blocking switching matrix which allows switching interconnections to be independently made and terminated without blocking subsequent interconnections on the same circuits. Various information signal functions, such as dial tone and ring-back, are selected by multiplex circuitry which is external of the switching matrix, so that all switching matrix trunks are available for voice and ring signal connections. The switching matrix is operated by a circuitry including a programmed digital computer, and provides substantial flexibility of control and service functions. Subscriber line status is monitored at all times, so that available special services can be accomplished by a subscriber in response to dialing selected digits.