TRANSLATORS AND mENTIFIERS IN SWITCHING SYSTEMS 601 



There are some cases dealing with the charges for telephone calls where 

 use is made of devices in which the input codes consist of two or more 

 factors, the arithmetical combination of which determines the output code. 

 Small scale electrical or clock-like mechanical computers are sometimes 

 used here; but in other cases the devices, because of the limited number of 

 possible outputs, are in reality systematic translators furnishing a limited 

 reference table, although there is a tendency to call them computers. 



Automatic computers could, of course, theoretically be used in many 

 cases to provide the translation afforded by systematic translators; and it 

 would also be possible to use one of the arbitrary translators mentioned in 

 the foregoing section. We would then be in a position to say that the proc- 

 esses of systematic translation would follow a pattern for various types of 

 appUcations. However, such arrangements could conceivably be economical 

 only in cases requiring a large variety of fixed translations or in cases 

 where the relationships between input and output codes were very compli- 

 cated. It seems to the writer most likely that, for the simple types of syste- 

 matic translation required in switching, special designs, each based on 

 well-known principles of efficient switching network circuitry arranged to 

 fit the special function, will continue to be the most economical. 



Arbitrary Changeable Translators 



Where there is no uniform relationship between the various possible 

 input and output codes of a translator, and in particular where the output 

 code associated with any given input code is subject to change, we can, in 

 general, resort to one of two things. We can provide a separate translator 

 for each input code, arranged so that it can be modified as the code associ- 

 ations are changed. This is seldom done in practice, and is economical only 

 where there are very few codes and the changes are infrequent. The usual 

 procedure is to provide a translator which can handle all or a substantial 

 portion of the required codes in a uniform manner without regard in its 

 detailed operation to the arbitrary and changeable relationship between the 

 input and output codes, but providing facilities for the changes required. 



The two changeable translators shown in Figs. 4 and 5, not only illustrate 

 methods of doing this with switches and relays, but also illustrate the 

 general principles used in all working translators of this type now in use. 

 The main variations are improvements to reduce costs, either of the translator 

 or elsewhere in the system, or to provide better tractabihty for changes. 



The general principle is that the over-all translation operation consists in 

 causing the input code to select a coding element which is capable of pro- 

 ducing the required output code. Changes in the output code associated 

 with the input code are made by wiring or other changes causing different 



