1006 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



Fig. 15 — No. 4A card translator. 



cig.bly in physical form, each taking advantage of the phenomenon of 

 some different area of the physical sciences — electrostatic, electromag- 

 netic, optic. Magnetic tapes" and drums^^ (Fig. 17), cores^^ (Fig. 18), 

 electrostatic storage in tubes^^' ^"^ (Fig. 19) and ferroelectrics^^' 2" 

 (Fig. 20) and photographic storage^' (Fig. 21) are available. 



Several properites of these memory devices are of interest. Being 

 electronic, the speed with which stored information may be read is of 

 primary interest. This is known as "access speed". Another property 

 of these common medium memory systems or devices is the ability to 

 change what has been written. If the changes can be made rapidly 

 enough they may be used in electronic systems in much the same man- 

 ner as relays are used in electromechanical systems to process informa- 

 tion. If the change must be made relatively infrequently, such as 

 changing photographic plates, they may be used as substitutes for the 

 type of memory in these systems which are provided by cross connec- 

 tions and wiring. The required fixed or semipermanent electronic mem- 

 ory may be characterized primarily b}^ a high reading speed, large 

 capacity, and the ability to hold stored information even during pro- 



