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Discussing 'non-standard byte sizes' with co-workers today, one mentioned hearing of soviet experiments with computers that used three-state bytes - and not just what is common today, 0, 1 and High Impedance meaning "absent on the bus", but actual trinary system, where the bits could achieve three logical values. Unfortunately, he was unable to provide any more details - nothing beyond "hearing about it."

Could someone provide more detail? Was there a computer system that was based on the trinary system? What was it? How did it work?

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    Could he be thinking of tri-state drivers? For example in the Commodor 64 the 6510 processor's address bus drivers are switched to a third "high impedance" state when the video chip needs to read memory. – David42 May 16 '16 at 14:58
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    en.wikipedia.org/wiki/Three-valued_logic and en.wikipedia.org/wiki/Ternary_computer cover much of this history and implementation. Not really retro, other than some old computers may have implemented logic in this manner. Modern computers and languages (i.e., SQL) can also implement trinary systems. – user12 May 16 '16 at 16:49
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    Furthermore, we should not be duplicating effort and results found on wikipedia and the usual vintage computer sites unless we have something significant to add. If the question can be edited to ask a specific, answerable question about trinary/ternary design as it applies to vintage systems, then it will be on-topic. – user12 May 17 '16 at 14:55
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    @jdv: I can concede the "general reference" point: I rushed here instead of doing my homework first. But I definitely disagree with your "off-topic" allegations. Reverse lookups like "Identify a system by unique set of features" is precisely the kind of question where Google is usually poor at providing answers, while Q&A sites give these answers quickly and painlessly. – SF. May 17 '16 at 18:01
  • This is a bad question, no matter if it's on topic or not. Simply typing (both) of your topics into Google leads straight to the Wikipedia article about the computer in question, making it obvious that you didn't do any preliminary research. See retrocomputing.stackexchange.com/help/how-to-ask and read the first guideline: "Have you thoroughly searched for an answer before asking your question?". – pipe May 19 '16 at 0:43
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These were probably the Setun computers, built in the Soviet Union between 1959 and 1965. It used balanced ternary (with the digits 1, 0, and -1) for computations, and a three-valued logic (I haven't been able to find which one) for operations. Electrically, it almost certainly used "ground", "positive voltage", and "negative voltage" as its signaling levels.

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    It didn't use negative voltage to represent -1. It used binary-coded trinary values, and both (0,0) and (1,1) meant trinary 0. It's explained in the Russian version of the Wikipedia page you link (you may be able to get some understanding of it via Google Translate). – Ruslan Oct 29 '16 at 14:25

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