A Laboratory Model Magnetic 



Drum Translator for Toll 



Switching Offices 



By F. G. BUHRENDORF, H. A. HENNING and O. J. MURPHY 



(Manuscript received January 24, 1956) 



A lahoratory model magnetic drum translator, capable of serving as a one- 

 to-one alternative to the card translator, has been built to study the problems 

 arising from the prospective use of microsecond pulse apparatus in a tele- 

 phone office environment. Electron tube amplifiers and, germanium diode 

 logic circuits supplement the drum information storage unit to provide the 

 functional operations required. Results of preliminary laboratory tests indi- 

 cate the feasibility of equipment of this kind for telephone switching control. 



INTRODUCTION 



The magnetic drum is one of the most widely used of the modern large- 

 capacity digital-data storage devices. It is used as a memory unit in many 

 of the present-day large-scale digital computers and in other applica- 

 tions such as inventory control of airline ticket reservations and traffic 

 control of airplanes in flight. Two of the properties of drums as storage 

 media have been considered particularly advantageous. One is the capac- 

 ity to store up to several hundred thousand bits of information in a com- 

 pact space at a low cost per bit; the other is the ability to keep the in- 

 formation in an easily alterable but nonvolatile form unaffected by power 

 failure or other interruptions of operation. In terms of the speed with 

 which information may be stored or i-(V'Overed, drum memories fall near 

 the middle of the present-day spectrum; they are very much faster than 

 punched paper tape or groups of telephone relays but are considerably 

 slower than cathode-ray tube or ferromagnetic-core storage devices. All 

 of the information stored on a drum may be read out during the course 

 of one complete revolution and, similarly, new information may be en- 

 tered anywhere in the storage space within the time of one revolution; 

 tlius the access time is ordinarily of the order of a few tens of milliseconds. 



It has already been pointed out^ that automatic telephone switching 



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