Setun (Russian: Сетунь) 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 most 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. 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 and production was halted in 1965. The characteristic operating memory consisted of 162 trits (ternary bits) with an additional 1944 trits on magnetic drum (total of about 3.3 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 model of the ternary computer, the Setun-70, was developed.
Setun was named after the Setun River, which ends near Moscow University.
DSSP (Dialog System for Structured Programming) is a programming language designed for Setun. It was created by students in the laboratory of Nikolay Brusentsov at the Computer Science department of the Moscow State University in 1980. The 32-bit version was created in 1989.
DSSP is similar to the Forth programming language; both are examples of stack-based languages.
The underlying ideology of DSSP was to reduce the semantic gaps between the human interface and the computer system. One principle was that there should only be one language to control and use the computer. Another was the principle of "one word of text – one word of machine code". DSSP's structure stays very close to the actual machine. It uses reverse Polish notation, a stack-oriented form of calculation.
The first document in English regarding this obscure language distinguishes DSSP from Forth in the following manner: "DSSP was not invented. It was found. That is why DSSP has not versions, but only extensions. Forth is created by practice. DSSP is created by theory. But they are similar and it is a fact of great importance."