The central control is composed of thousands of relatively simple logic circuits, intricately interconnected to perform the primary data processing functions of the No. 1 electronic switching system. This paper discusses both the circuit development of the basic modules and their application to the logic design of some of the high‐speed arithmetic circuits required in the central control. Special electrical design features, wiring rules, and circuit pack assignment procedures are also described.

No. 1 ESS provides a greater variety of services than any prior complex switching system, in central offices of greater capacity, but with more highly standardized equipment of much smaller volume. Much of the credit for this achievement is due to the use of fast electronic circuits under control of a generic program. Apparatus and equipment development was aimed at accenting the benefits in this system, disciplining options to concentrate demands on a few standard frame building blocks, minimizing the varieties and codes of apparatus to take advantage of economies inherent in large volume production, and combining these with flexibility and versatility in a dependable, maintainable, compatible system that will provide all services wanted now and in the future.

The No. 2 ESS achieves a standardized modular design that is easy to engineer, manufacture, install, operate, maintain, and administer. The use of much existing standard ESS hardware combined with thin film integrated circuits, plug‐in growth units, and judicious interframe connectors, has contributed to the development of an economically attractive system for the small central office market.