# Ternary computer

Ternary computer

Ternary computers (also sometimes referred to as trinary) use three-valued logic in their calculations.

History

One of the earliest calculating machines, built by Thomas Fowler entirely from wood in 1840, was a ternary computer. The only modern ternary computer Setun was built in the late 1950s in the Soviet Union at the Moscow State University, and it had notable advantages over the binary computers (such as lower electricity consumption and lower production cost) which eventually replaced it.

Balanced ternary

Ternary computing is commonly implemented in terms of balanced ternary, which uses the three digits -1, 0, and +1. The negative value of any balanced ternary digit can be obtained by replacing every + with a – and vice versa. It is easy to subtract a number by inverting the + and – digits and then using normal addition. Balanced ternary can express negative values as easily as positive ones, without the need for a leading negative sign as with decimal numbers. These advantages make some calculations more efficient in ternary than binary.

:"I often reflect that had the Ternary instead of the denary Notation been adopted in the Infancy of Society, machines something like the present would long ere this have been common, as the transition from mental to mechanical calculation would have been so very obvious and simple". ( [http://www.thomasfowler.org.uk/ Fowler, 1840] )

The future

With the advent of mass-produced binary components for computers, ternary computers have diminished to a small footnote in the history of computing. However, ternary logic's elegance and efficiency is predicted by Donald Knuth to bring them back into development in the future [D.E. Knuth, The Art of Computer Programming - Volume 2: Seminumerical Algorithms, pp. 190-192. Addison-Wesley, 2nd ed., 1980. ISBN 0-201-03822-6.] . Possible ways on how this can happen is by the combination of an optic computer with the ternary logic system [ [http://www.iop.org/EJ/abstract/1402-4896/2005/T118/025/ Ternary Optical Computer] ] The simple way to explain this is to compare it to binary. In binary computer, normally electronic computing, there are two values 1 or ON and 0 or OFF. A ternary computer using fiber optics could use three values: 0 or OFF, 1 or low, 2 or high. This future potential has also been remarked by certain companies as Hypres which is actively engaged in ternary computing. IBM also reports infrequently on ternary computing topics (in its papers), but it is not actively engaged in it.

Ternary computers in popular culture

* In Robert A. Heinlein's novel "Time Enough for Love", the sentient computers of Secundus, the planet on which part of the framing story is set, including Minerva, use an unbalanced ternary system. Minerva, in reporting a calculation result, says "three hundred forty one thousand six hundred forty... the original trinary readout is unit pair pair comma unit nil nil comma unit pair pair comma unit nil nil point nil (Chapter "Variations on a Theme III: Domestic Problems", Berkley books 19th printing [1982] page 99)

Literature

Hunger, Francis: SETUN. An Inquiry into the Soviet Ternary Computer. Institut für Buchkunst Leipzig, 2008, ISBN 3-932865-48-0 (English, German)

ee also

*Ternary numeral system

References

* [http://www.computer-museum.ru/english/setun.htm Development of ternary computers at Moscow State University]
* [http://www.mortati.com/glusker/fowler/ The ternary calculating machine of Thomas Fowler]
* [http://www.iop.org/EJ/abstract/1402-4896/2005/T118/025/ Ternary Optical computer]
* [http://www.trinary.cc/ Trinary.cc - logic gates used to build a ternary computer]

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