One early calculating machine, built by Thomas Fowler entirely from wood in 1840, operated in balanced ternary. The first modern, electronic ternary computer Setun was built in 1958 in the Soviet Union at the Moscow State University by Nikolay Brusentsov, and it had notable advantages over the binary computers which eventually replaced it (such as lower electricity consumption and lower production cost). In 1970 Brusentsov built an enhanced version of the computer, which he called Setun-70. In the USA, the ternary computer Ternac was developed in 1973.
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 binary 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.
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. One possible way this could happen is by combining an optical computer with the ternary logic system. A ternary computer using fiber optics could use dark as 0 and two orthogonal polarizations of light as 1 and −1. IBM also reports infrequently on ternary computing topics (in its papers), but it is not actively engaged in it.
The Josephson junction has been proposed as a balanced ternary memory cell, using circulating superconducting currents, either clockwise, counterclockwise, or off. "The advantages of the proposed memory circuit are capability of high speed computation, low power consumption and very simple construction with less number of elements due to the ternary operation."
Ternary computers in popular culture
In Robert A. Heinlein's novel Time Enough for Love, the sapient 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 ternary readout is unit pair pair comma unit nil nil comma unit pair pair comma unit nil nil point nil".
Virtual Adepts in Mage: The Ascension use ternary computers.
In the webcomic Schlock Mercenary (by Howard Tayler), every modern computer is a ternary computer. AIs use the extra digit as "maybe" in boolean (true/false) operations, thus having a much more intimate understanding of fuzzy logic than is possible with binary computers.
Hunger, Francis: SETUN. An Inquiry into the Soviet Ternary Computer. Institut für Buchkunst Leipzig, 2008, ISBN 3-932865-48-0 (English, German)
- Ternary numeral system
- Balanced ternary
- Skew binary number system
- Ternary logic
- Ternary signal
- Ternary flip-flap-flop
- Ternary SRAM
- Thomas Fowler biography
- Mark Glusker, David M. Hogan, Pamela Vass. "The Ternary Calculating Machine of Thomas Fowler," IEEE Annals of the History of Computing, vol. 27, no. 3, pp. 4-22, July-September 2005.
- Russian Virtual Computer Museum – Hall of Fame – Nikolay Petrovich Brusentsov, retrieved 2010-01-25.
- Trogemann, Georg; Nitussov, Alexander Y.; Ernst, Wolfgang (2001), Computing in Russia: the history of computer devices and information technology revealed, Vieweg+Teubner Verlag, pp. 19, 55, 57, 91, 104–107, ISBN 978-3-528-05757-2.
- 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.
- Ternary Optical Computer
- Chapter "Variations on a Theme III: Domestic Problems", Berkley books 19th printing  page 99
- Ternary "flip-flap-flop"
- Tunguska - Ternary Operating System emulator
- 3niti - Collaboration for Open Ternary Computer Development
- Development of ternary computers at Moscow State University
- The ternary calculating machine of Thomas Fowler
- Ternary Optical computer
- Trinary.cc – logic gates used to build a ternary computer
- PDF (6.6 MB)