1138 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



and mechanisms involved, have returned to other semiconductors — 

 particularly to silicon and germanium to obtain great improvements. 

 The interest in diodes was undoubtedly a factor in the chain of in- 

 vestigations which culminated in the invention of the transistor and the 

 development of the transistor has in turn accelerated the improvement 

 of the diode. The development of the transistor also has greatly increased 

 the demand for diodes. Replacing vacuum tubes by transistors, in 

 modem pulse communication and computer system design can expand 

 the potentialities of such systems since such systems, even more than 

 the telephone carrier, use large numbers of elements and the increments 

 of cost (initial unit cost, power consumption, space requirements, main- 

 tenance) all become vital. In a typical system there may be a dozen 

 diodes to every transistor or vacuum tube. In a vacuum tube system 

 the use of tube diodes is generally undesirable. In a transistor system 

 is is absurd. 



FIELD OF APPLICATION 



These two new and rapidly expanding applications of diodes (pulse 

 communication and computing) are amazingly simple in their basic 

 ideas and circuit building blocks. Practically all they do is: 



1 . Generate pulses or accept them from another source and regenerate 

 them. 



2. Store pulses. 



3. Route pulses to a desired output. 



The complexity of the modern computer with its thousands of tubes 

 or transistors and diodes lies in the number of operations, not in the 

 individual operation itself. The modern computer is capable of solving 

 compex mathematical problems involving any of the normal mathe- 

 matical operations and may do it primarily with diode networks — aided 

 by amplifiers to compensate for losses, and delay networks, or timing 

 devices, to insure that processes take place in the proper sequence\ The 

 diode networks, which are the body of a modern computer or pulse 

 communication system, are "gates" and routing circuits which, by con- 

 trolling and guiding the passage of pulses, are capable of performing all 

 the logical processes required. 



TYPES OF DIODE GATES 



A "gate", for our purposes, is an electrical device with an input, an 

 output, and one or more control inputs. The control inputs and the other 



^ Felker, Regenerative Amplifier for Digital Computer Applications, Proc. 

 I.Il.E., 40, Nov., 1952. Chen, Diode Coincidence and Mixing circuits, Proc, 38, 

 May, 1950. 



