Building The First Ternary Microprocessor

Your computer uses ones and zeros to represent data. There’s no real reason for be the basic unit of information in a computer to be only a one or zero, though. It’s a historical choice that is common because of convention, like driving on one side of the road or having right-hand threads on bolts and screws. In fact, computers can be more efficient if they’re built using different number systems. Base 3, or ternary, computing is more efficient at computation and actually makes the design of the computer easier.

For the 2016 Hackaday Superconference, Jessie Tank gave a talk on what she’s been working on for the past few years. It’s a ternary computer, built with ones, zeros, and negative ones. This balanced ternary system is, ‘Perhaps the prettiest number system of all,’ writes Donald Knuth, and now this number system has made it into silicon as a real microprocessor.

After sixty or seventy years of computing with only ones and zeros, why would anyone want to move from bits to trits? Radix economy, or the number of digits required to express a number in a particular base, plays a big part. The most efficient number system isn’t binary or ternary – it’s base e, or 2.718. Barring the invention of an irrational number of transistors, base three is the most efficient way to store numbers in memory.

Given that ternary computing is so efficient, why hasn’t it ever been done before? Well, it has. The SETUN was a ternary computer built by a Soviet university in the late 1950s. Like Jessie’s computer, it used a balanced ternary design using vacuum tubes. The SETUN is the most modern ternary computer that has ever made it to production, until now.

For the last few years Jessie has been working on a ternary computer based on ICs and integrated circuits, making it much smaller than its vacuum tube ancestor. Basically, the design for this ternary logic relies on split rails – a negative voltage, a positive voltage, and ground. The logic is still just NANDs and NORs (ternary logic does provide more than two universal logic gates, but that’s just needlessly complicated), and ternary muxes, adders, and XORs are built just like their binary counterparts.

This isn’t the first time we’ve heard about Jessie’s ternary computer. It was an entry for the Hackaday Prize two years ago, and she made it down to our 10th-anniversary conference to speak on this weird computer architecture. Over the last two years, Jessie found a team and funding to turn these sketches on engineering notebook paper into circuits on real silicon. Turning this chip into a real computer – think something along the lines of a microcomputer trainer from the 1970s – will really only require a few switches, LEDs, and a nice enclosure.

Where will the ternary computer go in the future? According to Jessie, the Internet of Things. This elicited a few groans in the audience during her talk, but it does make sense: that’s a growing market where efficiency matters, and we’re more than happy to see something questioning the foundations of computer architecture make it to market.

Filed under: cons