Maybe The Oldest Computer, Probably The Oddest

[Tadao Hamada] works for Fujitsu Tokki, a subsidiary of the more famous Fujitsu. In 1956, Fujitsu decided to compete with IBM and built a relay-based computer, the FACOM128. The computer takes up 70 square meters and weighs about 3 tons. By 1959, they’d learned enough to make a FACOM128B model that was improved. [Hamada’s] job is to keep one of these beasts operational at Fujitsu’s Numazu plant. According to the Japanese Computer Museum, it may be the oldest working computer.

The relays in the computer were adapted from telephone switch networks. The computer had an index register and an interrupt. It used a biquinary (base 5) system and it could automatically detect errors and recompute by using redundancy (each decimal digit took 7 bits) and checking results against their complements, separately calculated.

There’s not a lot of information about the old machine on the Internet and what there is tends to be in Japanese. The computer was made for speed (relatively speaking) and uses asynchronous control so it doesn’t have to clock at a rate suitable for the slowest part of the machine.

A word was 69 bits, although that’s misleading because some of that was dedicated to the automated self-check function. There were 180 words of general-purpose memory. There were also specialized banks of memory for paper tape, the printer, and other items. One read only memory held common constants needed in calculations. The computer even has a floating point unit that can hold 8 significant digits and an exponent between -19 and +19.

The FACOM128 series was a relay computer although at the time tube-based computers were appearing. However, experience with earlier computers convinced Fujitsu that computers needed to be error free. At the time, a relay was much more reliable than a tube and combined with the self-checking and automatic re-execution, the FACOM128 provided a very reliable computing platform for its day. The 128B was faster, added some instructions such as extended-length addition and subtraction, provided user-defined constants, and also had better documentation.

38 thoughts on “Maybe The Oldest Computer, Probably The Oddest

    1. The Japanese Computer History Museum claims it might be the oldest but perhaps it is on some differentiation like commercially produced or something like that. Also, I think WITCH got restored although I’m not sure how long the FACOM has ever been dormant.

        1. As far as I can tell it’s only there to be on display. But it does operate because they talk about how impressed visitors are when it starts clicking and clacking.

      1. Which would then be the Zuse Z1. Konrad Zuse himself made a replica for the Deutsche Technikmuseum Berlin as the original one was destroyed in the war. His oldest surviving machine is the Z3, which was only saved because he tricked the Wehrmacht and told them that these crates over there where “Kriegswichtig”, for the war effort.

    1. All the bombas (and British bombes) were destroyed after the war. No originals are left. The Dekatron is the oldest working computer; restoration is a moot point, since the tubes and relays had to be replaced all the time. Ship of Theseus!

    2. That was an automated Enigma key checking mechanism, not a computer. Basically 6 interconected Enigma mechanisms (one for each rotor order) with anciliary equipment to automate the checking process. Brilliant achievement, but if it’s a computer, so is an enigma machine.

  1. The error-checking and recomputing is brilliant! Sure, transistors changed everything but before that breakthrough this would have been the most reliable computer. The design seems entirely alien but it was also cutting-edge tech that was both fast and reliable. I love it!

    1. This is to be expected in Conroe. One of the broadcast facilities in Missouri City was still using a Heathkit Z80 desktop for personnel access control and tower elevator control until just a few years ago. It was maintained impeccably and worked flawlessly for decades. There are hundreds of reasons to take these computers offline and only unique individuals with vision and intelligence to keep them online. How unique and cool.

      1. To be fair, the report button should not be at the bottom of the post, it’s too easy to confuse it with a reply button. A better place for it might be at the top right, possibly followed by a very clear confirmation form.

        1. This matter has been brought up so many times before, but I still see absolutely nothing being done about it. For gods sake, just pay a programmer a couple of grand to do it and be done!

    1. Perhaps different voltages for different values. There was at least one computer that used trinary logic.
      Or they just used base 5 numbers encoded in binary. There were computers that used base 10 system with BCD…

    2. biquinary has both binary – base 2 and quinary base 5

      In this application numbers 0 to 4 is represented by one of five relays being on. The same five relays also represent the numbers 5 to 9. There are an additional two relays , one selects the range 0 to 4 and the other selects the range 5 to 9.

      This system is chosen so that there are exactly two relays on for any valid decimal digit.

      The operation time can vary a lot between relays because there are a lot of squared relationships in the math behind the physics of their operating principles.

      As this system is asynchronous it needs to have a valid state after a transition to propagate the process.

      1. Thank you. So each decimal digit is represented by 7 relays. When they say a word is “69 bits”, they can’t mean 69 biquinary digits (69 * 7 = 483 relays), they must mean 69 relays which would be 9 decimal digits.

  2. The Zuse Z4 originally went into operation in 1950 at ETH Zurich, and is now in a museum in Munich. That was also an electromechanical computer. That Fujitsu might well be the oldest machine that’s actually still in operational condition though.

    1. I read about that years ago and then couldn’t find it again. That’s a computer with 113 vacuum tubes. It does have a lot of germanium diodes, but that is amazing. It’s slow, at 500 ops a second but it can run FORTRAN programs. The debugger is an oscilloscope.

    1. I played with this machine when I worked for Fujitsu. Does about 1.5 adds per second and makes a helluva noise. Much more fun than the submarine cable repeaters nearby.

  3. I remember reading an article in 50’s on how to build a relay computer; from Radio-electronics, I believe. I read the article and learned how to make and/or/flip-flops (i.e. memory) and then wondered why anybody would bother do it :):) Why go to all that trouble to make an “and” ? I was much younger then. LOL
    This whole thing was probably based on: https://en.wikipedia.org/wiki/Simon_(computer)

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