716 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1956 



from the "^" which was originally written in cell 4. In many applica 

 tions a much larger "influence factor" may be tolerable, but this usually] 

 requires greater elaboration of the signal detecting devices. The cell size 

 is also influenced by physical constants such as design of the head, prop- 

 erties of the medium, and dimensional clearances. A discussion of suchj 

 factors is outside the scope of this paper but it is not unreasonable to i 

 hope for an improvement of two-to-one in packing factor in future de-» 

 signs. 



Reading Synchronization 



The magnetic drum used for the translator provides 80 tracks. About 

 sixteen microseconds is required for each cell in a track to pass under its 

 head. Information occupying the same slot on the drum (so-called be- J 

 cause of its obvious relationship to the term "time-slot" commonly used 

 in the digital computer field) is presented at the various heads essenti- 

 ally, but not exactly, simultaneously. Departure from exact simultaneity 

 is occasioned by small variations in the shapes and amplitudes of the 

 output waves shown typically as line C in Fig. 3, and by small time-vari- 

 ations occurring in the writing process, as applied to the ^^arious tracks. 



To achieve exact simultaneity, as required for certain subsequent op- 

 erations of the translator circuitry, narrow "Read Synchronizing" pulses 

 are produced by the synchronizing circuit previously mentioned. These 

 pulses are located, within the time boundaries of the cells, so that they 

 fall approximately at the center of the broad output pulses from the 

 reading amplifiers and thus permit the latter to be sampled. This rela- 

 tionship is indicated in lines D'and E of Fig. 3. Similar pulses, slightly 

 displaced in time, are used to control the writing operations, and are des- 

 ignated "Write Synchronizing" pulses. The necessity for the time-shift 

 is apparent from an examination of lines A and E of Fig. 3. 



This condensed explanation of the technology of magnetic drum digi- 

 tal data storage devices, particularly as applied to the translator drum, 

 should serve as sufficient background for the description of the translator 

 wherein the drum is but one part of a large ensemble of apparatus. 



THE JOH WHICH THE CAKD TRANSLATOR NOW DOES 



It will be advantageous to examine very briefly the card translator and 

 its functions in the No. 4A toll switching system so that the analogous 

 operation of the magnetic di'um equivalent may be more readil,y ex- 

 plained. A more detailed description is given in Reference 4. 



'l'li(> (I'Munnds of nation wid(> toll dialing rcniuire a \'ery extonsi\-c vvp- 







