COMMON' CONTROL SWITCHING SYSTEMS 1087 



portaiii about the future of this method of operation. It appeared to 

 them that the greatest promise in tlie use of automatic api)aratus was 

 ill distributing calls to manual "A" operators and in the elimination of 

 tiie "B" operators. Consideration was being given to systems capable of 

 operating on either a semi-mechanical or a full mechanical basis depend- 

 ing on whether the dial was located at the "A" board or at the sub- 

 scriber's station. Development was also under way to provide arrange- 

 ments for trunking calls between dial offices and to overcome the numerous 

 weaknesses and deficiencies of existing dial systems. 



The Strowger Company, the Bell System, and several other companies 

 were plaiming or developing automatic and semiautomatic systems at 

 that time. These included the full automatic, the network automatic, 

 the automatic operator, and the semiautomatic. Short descriptions of 

 some of them follow. 



EARLY FULL AUTOMATIC SYSTEMS 



The full automatic systems were mostly direct dial control. They 

 included the Strowger, the Western Electric 100-line and 20-line, the 

 Clark, the Faller* and the Lorimer systems. 



The Strowger system of the middle 1890's provided 100-point two- 

 digit selectors, one for each line. For each group of 100 lines the 100 

 outlets of each selector were multipled to the corresponding outlets of 

 the other selectors serving the group. Each outlet of the group ran to a 

 two-digit connector, each connector having access to 100 lines. Thus 

 every group of 100 lines had 100 selectors and a maximum of 100 con- 

 nectors and could reach 10,000 lines in a full office. Each group of con- 

 nectors, up to the maximum of 100 connectors per group, had a multiple 

 of 100 terminating lines. This was therefore a 4-digit single-office system 

 theoretically of 10,000 lines capacity, requiring 1 selector and 1 connector 

 per line. Subscribers in a given originating group of 100 lines had only 

 one path to a particular terminating group of 100 lines. Since a selector 

 was pro\'ided for each line, no dial tone was necessary. The switches used 

 the familiar up and around motion. The exchanges of this type that 

 were installed were small, the largest being in the order of 1000-line 

 capacity. This type was followed by a new arrangement when automatic 

 trinik selection was introduced. This provided multiple paths to each 

 terminating group of 100 lines; the selector at this stage became a single- 

 digit switch. 



The Western Electric 100-line system could actually serve onl}- 99 



*U. S. Patent 686,892— Ernest A. Faller— Nov. 19, 1901. 



