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An immediate consequence of stored program control is automation of exchange functions and introduction of a variety of new telephony features to subscribers.
A telephone exchange must run continuously without interruption at all times, by implementing a [[fault-tolerant design]]. Early trials of electronics and computers in the control sub systems of an exchange were successful and resulted in the development of fully electronic systems, in which the switching network was also electronic. A trial system with stored program control was installed in [[Morris, Illinois]] in 1960. It used a [[flying-spot store]] with a word size of 18 bits for semi-permanent program and parameter storage, and a barrier-grid memory for random access working memory.<ref>A. E. Joel, ''An Experimental Electronic Switching System'', Bell Laboratory Record, October 1958 p.359</ref> The world’s first electronic switching system for permanent production use, the [[No.1 ESS]], was commissioned by AT&T at [[Succasunna, New Jersey]], in May 1965. By 1974, AT&T had installed 475 No. 1ESS systems. In the 1980s SPC displaced electromechanical switching in the telecommunication industry, hence the term lost all but historical interest. Today SPC is
The attempts to replace the electromechanical switching matrices by semiconductor cross point switches were not immediately successful, particularly in large exchanges. As a result, many space division switching systems used electromechanical switching networks with SPC
==Types==
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