How to connect to a program-controlled exchange

Stored program control (SPC) is a telecommunications technology for. Its characteristic is that the switching system is controlled by a computer program stored in a memory in the switching system. SPC was the enabling technology of (ESS) developed in the in the 1950s, and may be considered the third generation of switching technology. Stored program control was invented in 1954 by scientist, who reasoned that. [pdf]