1092 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



A necessary feature of systems employing translation of a series of 

 digits such as an office code is digit storage. It was only a small step 

 from the concepts of translation and digit storage to arrangements which 

 provided these features in common circuits. Common controls with 

 translation were first employed in the rotary system. 



THE ROTARY AND PANEL SYSTEM DEVELOPMENTS 



The rotary system was a full-fledged common-control system using 

 register-senders to store the dialed information, to translate it to control 

 the two-hundred point ten-level power-driven switches in selecting out- 

 going trunks from the originating office and in making line selections in 

 the terminating office. The translation of the digits used for selecting 

 trunks was changeable, but the translation of the numerical digits was 

 fixed in permanent wiring of the register-senders. 



In a search for less expensive cabling arrangements than those required 

 by the rotary system, the panel bank employing punched metallic strips 

 was developed. Each bank in the selectors of this system can accommo- 

 date 100 outlets with three wires per outlet, and five banks are stacked 

 into a frame over which 60 power-driven selectors can hunt. For several 

 years, starting in 1907, parallel development of the rotary and panel 

 systems was carried on and desirable features of one were incorporated 

 in the other. The panel system also has register-senders with changeable 

 translation for selecting trunks and fixed translation for controlling 

 selections in the terminating equipment. The major differences in the 

 early designs of rotary and panel were due to the different access of the 

 two systems and to differencesin the methods of controlling the selectors. 

 Both panel and rotary use revertive pulsing to control the selections. 

 With revertive pulsing as the selectors progress they send back pulses 

 which the sender counts. When a selector reaches the desired position, 

 the sender stops it by opening the pulsing circuit. Both panel and rotary, 

 like the Lorimer system, use a continuously operated power dri^'e com- 

 mon to a number of switches because the increased size of switch which 

 the greater access of these systems required, made a separate power 

 drive economical. 



The panel and rotary systems were originally designed for semi- 

 mechanical operation with automatic distribution of calls to operators 

 as a possible adjunct and with provision for full automatic operation if 

 it proved desirable, by locating the dial or some other calling device at 

 the subscriber's station rather than at the operator's position. This was a 

 reasonable plan when development of these systems was started. Studies 

 indicated that semi-mechanical systems could reduce the number of 



