MAGNETIC DRUM TRANSLATOR FOR TOLL SAVITCHING OFFICES 717 



ertoire of translations between destination codes and routing instruc- 

 tions, and it must be possible to change the routing instructions with 

 ease. The card translator fulfills these requirements. Each individual 

 translation item is contained on a metallic card; the output code of rout- 

 ing instructions is in the form of selectively enlarged perforations in the 

 perforated field of the card, arranged so as to be read by photoelectric 

 means, and the input code, which identifies the card for purposes of selec- 

 tion, appears in the form of tabs projecting downward from the bottom 

 edge. Each card is capable of holding a total of 154 bits of information, 

 input and output, and somewhat over 1,000 cards are stacked in a bin in 

 each card translator mechanism. 



It is possible to classify the elements of any translator into three broad 

 categories: the memory unit, the translation selecting unit, and the trans- 

 lation delivery unit. In the card translator the memory unit is, of course, 

 I the group of cards; the translation selecting unit consists of code bars, 

 ' electro-mechanically actuated, for displacing a selected card sufficiently 

 ' so that it may be "read." It also contains a network of relays which per- 

 form the function of checking the authenticity of the input codes applied 

 I to the code bars. The translation delivery unit consists, in the main, of a 

 number of output channels, each originating with a light beam for prob- 

 I iiig one of the code elements (a bit of output information) on the card. 

 [ Each output channel contains a photo-transistor, a transistor amplifier, 

 a cold cathode gas tube circuit which has been designated a "channel 

 output detector" and a register relay. The register relays perform work 

 ' functions and therefore are located separately from the translator; some 



are in the decoders, others in the markers. 



! In the 4A office, the card translator is one of several items of common 



I control ecjuipment which cooperate to establish the talking connections. 



( )ther items are the sender, the decoder, and the marker. The sender re- 



I ceives and registers and subsequently transmits the decimal digits of the 



! called designation; the decoder receives the code digits (from 3 to in 



' number) from the sender and submits them to the translator for con- 



; \ersion into information needed for the proper routing of the call; and 



1 the marker selects an outgoing trunk and establishes a transmission path 



by operating the crossbar switches. Since this common control equipment 



is associated with any one call for only the short interval necessary to 



j establish the talking-circuit connection, its speed of operation is a matter 



of considerable importance. 



It is ob\^ious that the decoder is the intermediary between the trans- 



I lator and the remainder of the office. Each decoder, of which there are a 



maximum of 18 in a large office, has exclusively associated with itself a 



