Setun () was a computer developed in 1958 at Moscow State University. It was built under the leadership of Sergei Sobolev and Nikolay Brusentsov. It was the first modern ternary computer, using the balanced ternary numeral system and three-valued ternary logic instead of the two-valued binary logic prevalent in other computers.
Overview
The computer was built to fulfill the needs of Moscow State University. It was manufactured at the Kazan Mathematical plant. Fifty computers were built from 1959 until 1965, when production was halted. The characteristic operating memory consisted of 81 words of memory, each word composed of 18 trits (ternary digits) with additional 1944 words on magnetic drum (total of about 7 KB). Between 1965 and 1970, a regular binary computer was used at Moscow State University to replace it. Although this replacement binary computer performed equally well, it was 2.5 times the cost of the Setun.
In 1970, a new ternary computer architecture, the Setun-70, was developed. Edsger W. Dijkstra's ideas of structured programming were implemented in the hardware of this computer. The short instructions set was developed and implemented by Nikolay Brusentsov independently from RISC architecture principles.
At the time, Brusentsov was a graduate (equivalent to a master degree, see Education in Russia, traditional model) at Moscow State University, who was graduated from the Moscow Energy Institute. Before appointing Brusentsov as the executive designer of Setun computer, Sobolev transferred Brusentsov to the Mechanics-Mathematics department and sent him to Gutenmakher's laboratory at the Institute for Precision Mechanics to gain relevant experience. To Brusentsov, this was an invaluable experience. In the lab, he had access to the lab's computers and their supporting documentation, which Brusentsov found being "technically weak". Brusentsov then decided to use a ternary number system.
Setun computer
Sobolev continued to support the project both by finding assistants and participating in the discussions. In 1956, Brusentsov started the design with four engineers and five technicians plus himself. The whole team worked in a 60-square-meter room with laboratory tables, where they designed and assembled the machine by hand. Zhogolev worked as the main programmer, and together with him, Brusentsov developed the computer architecture of Setun. In 1958, the team grew to 20 people, and the first model of the Setun computer was assembled. The name Setun comes from a river near the University.
At user seminars on the Setun computers—held at Moscow State University (1965), the Lyudinovo Diesel-Locomotive Plant (1968), and Irkutsk Polytechnic Institute (1969)—dozens of reports were presented on successful real-world applications for the national economy. Owing to its balanced ternary code, Setun turned out to be a truly universal, easily programmable, and highly efficient computing instrument. It earned a strong reputation, notably as an educational tool for teaching computational mathematics in more than thirty universities. At the Zhukovsky Air Force Engineering Academy, Setun even became the platform for the first automated computer-based learning system.
Critics
Brian Hayes argues in his article Third Base that Brusentsov did not realize the theoretical advantage of the base 3 system:
Ternary compared to binary
Balanced ternary systems and ternary computers are not unprecedented in history. Thomas Fowler built a mechanical computer in 1840 using balanced ternary system. The balanced ternary representation of numbers and its related arithmetics was applied in number theory back to Leonhard Euler and was briefly discussed by Claude Shannon in his paper "A Symmetrical Notation for Numbers" published in 1950.
Despite the ternary design never becoming massively produced, there have been discussions on the advantages of the ternary system over the binary system, and great interest was present on the ternary and more generally on the multi-valued logic systems in the academy.
Advantages
Brusentsov found the ternary number system superior to the binary number system: it allowed him to create very simple and reliable elements, and he needed only one seventh as many elements as Gutenmakher's computers. The power source requirements were also significantly reduced because fewer magnetic rods and diodes were used. He also found the natural number-coding system used in the ternary system superior over the direct, reciprocal and supplementary number coding used in the binary system. He maintained that the ternary system is superior to binary in most aspects and published several papers advocating the ternary system from 1985 to 2014.
The symmetric nature of balanced ternary logic allows for natural representation of negative numbers.
The ternary system is also more efficient from an information theory perspective. Donald Knuth wrote in his book The art of Computer Programming that "Perhaps the symmetric properties and simple arithmetic of this number system will prove to be quite important some day," noting that,