In such switchboards an operator at one of the boards or positions may complete the connection herself between any two lines terminating at her own board.  If, however, the line called for terminates at another one of the boards, the operator makes use of the transfer or trunk line extending to that board, and the operator at this latter board completes the connection, so that the two subscribers’ lines are connected through the trunk or transfer line.  A distinguishing feature, therefore, in the operation of so-called transfer switchboards, is that an operator can not always complete a connection herself, the connection frequently requiring the attention of two operators.

Transfer systems are not now largely used, the multiple switchboard having almost entirely supplanted them in manual exchanges of such size as to be beyond the limitation of the simple switchboard.  At multi-office manual exchanges, however, where there are a number of multiple switchboards employed at various central offices, the same sort of a requirement exists as that which was met by the provision of trunk lines between the various simple switchboards in a transfer system.  Obviously, the lines in one central office must be connected to those of another in order to give universal service in the community in which the exchange operates.  For this purpose inter-office trunk lines are used, the arrangement being such that when an operator at one office receives a call for a subscriber in another office, she will proceed to connect the calling subscriber’s line, not directly with the line of the called subscriber because that particular line is not within her reach, but rather with a trunk line leading to the office in which the called-for subscriber’s line terminates; having done this she will then inform an operator at that second office of the connection desired, usually by means of a so-called order-wire circuit.  The connection between the trunk line so used and the line of the called-for subscriber will then be completed by the connecting link or trunk line extending between the two offices.

In such cases the multiple switchboard at each office is divided into two portions, termed respectively the A board and the B board.  Each of these boards, with the exception that will be pointed out in a subsequent chapter, is provided with a full complement of multiple jacks for all of the lines entering that office.  At the A board are located operators, called A operators, who answer all the calls from the subscribers whose lines terminate in that office.  In the case of calls for lines in that same office, they complete the connection themselves without the assistance of the other operators.  On the other hand, the calls for lines in another office are handled through trunk lines leading to that other office, as before described, and these trunk lines always terminate in the B board at that office.  The B operators are, therefore, those operators who receive the calls over trunk lines and complete the connection with the line of the subscriber desired.