Stored Program Control exchange (SPC) is the technical name used for telephone exchanges controlled by a computer program stored in the memory of the system. Early exchanges such as Strowger, panel, rotary, and crossbar switches were electromechanical and had no software control. SPC was introduced on a small scale in so called electronic switching systems in the 1960s (the 101ESS PBX was a minor Bell System example) and on a large scale in the 1970s (1ESS switch from Bell System, AXE telephone exchange from Ericsson). SPC allowed more sophisticated calling features. As SPC exchanges evolved, reliability and versatility increased. In the 1980s SPC completely took over the industry, making the term redundant except for historical interest.
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