STORED PROGRAM CONTROL
Conrol in telephone exchanges developed from individual control of each switch on step-by-step exchanges to the use of a small number of complex centralised units in so called common control exchanges, which were mainly crossbar or reed. Common control units were originally completely electromechanical, using the same basic type of relay which had been used for many years in earlier exchanges. Electronic common control had to wait for the popularisation of the transistor and the printed circuit board before it became truly economic.
The use of computers to conrol telephone exchange switching is called Stored Program Control or SPC. This has been defined as the control of an automatic switching arrangement in which call ...
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