Automatic private branch exchange development in San Francisco

A few years ago, the majority, in fact a very large majority, of those interested in the technical aspect of the telephone, considered what is now well known as the automatic telephone, impracticable for central office service, even in single office districts. This erroneous idea has long since been dispelled by the installation and subsequent satisfactory operation of numerous extensive automatic systems, many of which each include a number of large central offices. Following the satisfactory development of the central office, it was soon realized that a great saving could be made in the exterior cable plant, if small unattended or partially attended sub-offices, as they are now called, could be built, to give efficient and economical service. It will suffice here to say that the experiment was tried with the result that the sub-office is now considered a necessary adjunct to the automatic central office. The purpose of this paper, is to show that the unattended sub-office is by no means the limit of sub-division and that such sub-division has now been successfully extended to include two somewhat distinct types of private branch exchanges, one adapted to meet the requirements of apartment houses and family hotels and the other the more exacting requirements of all classes of commercial organizations and business houses. The most noticeable difference between the two is that the former is arranged, apart from some minor features, to give “in” and “out” exchange service only, while the latter is arranged to give “local inter-communication” as well. The automatic system has not as yet been applied to the larger commercial hotels where the total annual cost of the equipment involved is great in comparison with the average revenue derived per telephone. At the present time, the first cost of automatic apparatus prohibits its general use in such places.