back to article Brit 2.5-tonne nuke calculator is World's Oldest Working Computer

Britain's hefty Harwell Dekatron is back in the Guinness Book of World Records after being recognised - for the second time - as the world's oldest working digital computer. The 2.5-tonne number-crunching goliath began life at the Atomic Energy Research Establishment in Harwell, Oxfordshire, in 1951, and put reliability over …


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  1. John Latham


    Looked it up on Wikipedia. Want.

    1. Don Jefe

      Re: Dekatron

      Agreed! I wonder if the light was necessary or they just knew how cool it would look.

      1. BobvonKnobloch
        Thumb Up

        Re: Dekatron

        The light is how it works.

        It's essentially an array of neons and when one strikes, the voltage is too low for the others. An impulse causes the 'lit' segment to change to the next one.

        Used to design things with these, rtl logic took quite a while to provide similar functionality.

      2. BobvonKnobloch

        Re: Dekatron

        BTW maybe a 'which side of the Atlantic' thing, but I have never, until now, seen it spelt with a 'k'.

        For me it remains a decatron.

        1. Anonymous Coward
          Anonymous Coward

          Re: Dekatron

          > but I have never, until now, seen it spelt with a 'k'.

          From wiki:

          "Dekatron," now a generic trademark, was the brand name used by the British Ericsson Telephones Limited (ETL), of Beeston, Nottingham

  2. Silverburn

    Dekatron tubes 'Gerry Anderson' flashback to Space:1999 there for a moment.

    Carry on. I'm ok now.

    1. Spoonsinger

      Re: 'Gerry Anderson' flashback to Space:1999 there for a moment.'

      Good man! Light a cigar in a high oxygen environment :-)

      1. Anonymous Coward

        Re: 'Gerry Anderson' flashback to Space:1999 there for a moment.'

        I don't like smoking at all...

        But I'd kind of like to see that.......

        As apprentice "Makers of Boils" - we got force fed safety videos of dummies dressed in overall's, getting the dust blown off them with pure oxygen, from an oxygen aceteylene cutting torch....

        Add a source of ignition...

        Sort of impressive.

        But not exactly "in the confines of an oxygen filled space capsule" effect, with the LOX bottles and lines in situ as well.

        Satan - Oxygen lights my fire.

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  4. FartingHippo

    "Those Specs In Full"

    Yet no mention of processing capability.

    I'm pretty curious, for one.

    1. Anonymous Coward
      Anonymous Coward

      Re: "Those Specs In Full"

      Isn't it around 0.0000000001Gflops?

      1. Danny 14

        Re: "Those Specs In Full"

        12 legumes per second apparantly. Only 4 norks a week though :(

  5. John Robson Silver badge

    BogoMIPS (or mBogoMIPS?)

    We're interested.

  6. NomNomNom

    what did it calculate?

    1. Anonymous Coward
      Anonymous Coward


      What was the question?

      1. Anonymous Coward
        Anonymous Coward

        What is six multiplied by seven?

        1. Anonymous Coward

          re: AC @16:24

          Never read the book, have you? It's What do you get when you multiply six by nine.

          1. Don Jefe

            Re: re: AC @16:24

            That's to obvious.

          2. Toastan Buttar

            Re: re: AC @16:24

            No-one writes jokes in base 13.

    2. Frumious Bandersnatch

      what did it calculate?

      I have it on good authority that it came up with "BOOBIES"

  7. Longrod_von_Hugendong

    Still better speed...

    than most versions of windows. :D

    In all seriousness, they did a fantastic job of recovery and restoration to make sure an important machine is kept for future generations to enjoy and learn from.

  8. I ain't Spartacus Gold badge

    Now all you need to do is slap on a touch-screen and a really big battery, and Samsung have got the Galaxy Note III...

    1. Rampant Spaniel

      and the suit from Apple will follow after a swift visit to the patent office. They'll be putting this new vacuum tubes tech in the iphone 6 to make it lighter ;-)

      It's great to see it back up and running! I know it's very Beardy but theres something awesome about those old machines, they're not just beige boxes (ok Sun have made some nice kit in their time, but its all just boxes really), stuff with tubes and lights is just so 1970's scifi :-)

      1. I ain't Spartacus Gold badge

        Don't forget the tapes? You've got to have giant reel-to-reel tape recorders, or it ain't a proper computer!

        I agree with you on the sheer excellent-ousity of getting it working again though.

        1. Pypes

          I hope that's punched metal tape your talking about son, non of that new fangled magnetic stuff.

  9. Admiral Grace Hopper

    And if you talk to the people working on it,

    They are immensely knowledgable and keen to share that knowledge.

    The gentleman ("I know valves, not computers") who took time out to explain the machine and how it worked to my niece last year, then got her to step it through to demonstrate how it processed a calculation deserves my thanks. If there's been a bar handy, I'd have offered him a pint. Thank you Sir!

    1. messele
      Thumb Up

      Re: And if you talk to the people working on it,

      There used to be a bar in the manor house. No idea if they are still licensed. Otherwise head out the main entrance, turn left on to Church Green Road and the Eight Belles is down the bottom on the right.

      Dunno why I felt the need to tell you all that but it would be nice to think we could get the engineers / guides sloshed one by one on a daily basis :)

  10. The FunkeyGibbon
    Thumb Up

    Bletchley Park is awesome.

    If you've not visited you should! It's a brilliant site with a lot of very interesting history and a total geek-gasam inducing collection of computers. :-)

    1. PeterO

      Re: Bletchley Park is awesome.

      If all you want to do is visit the "geek-gasam inducing collection of computers", then you don't want to visit the Bletchley Park Trust as such as their tours cover the war time story (intersting as it is) but don't even include a visit to Colossus any more. What you want to do is visit "The National Museum of Computing" which is a separate museum located on the BP site.

    2. Anonymous Coward
      Anonymous Coward

      Re: Bletchley Park is awesome.

      Agree totally. It is a fantastic place to visit, especially for us gentlemen of a certain incoming middle youth age bracket. And the people there are so nice and knowledgeable.

      The Computer Science Museum there run programming workshops for kids to play with BBC Micros etc... It works well because the machines so immediate. When asked 'how long does it take to start a BBC Micro so it's ready to use?' the guesses ranged from 5 minutes to half an hour (!). Instead: One flick of the power switch, half a second and one beep:

      BBC Computer 32K

      Acorn DFS


      > rem The world starts here...


      According to the guy I spoke with, the kids loved it.

  11. Quxy


    ...but can it run Crysis?

    1. Dave 126 Silver badge

      Re: Yeah...

      At what frame rate?

      Don't think it blends, though.

      1. Michael H.F. Wilkinson

        Re: Yeah...

        More likely it will crush the blender!

  12. Dave 126 Silver badge

    I love it... after using computers to fight fascism in Europe, we British then use computing for our second highest priority: ensuring we have enough cups of tea and cake.

    1. Steve the Cynic

      Lyons Electronic Office was a contemporary of this beastie, actually.

      It lead eventually to a weird conversation I had in a job interview. The company's product was marketed as being so easy to use that even your mother could use it. Hmm. So in the interview I remarked on the obvious flaw with this line of "reasoning": my mother, in the 1960s, was a senior programmer for LEO (the company) on LEO III machines. Saying it was so easy even she could use it isn't really a strong message...

      (Yes, I do know what was meant, which is why I said it to be read as teasing them slightly...)

      1. Anonymous Coward
        Anonymous Coward

        did u get the job after your pedantry?

        1. Steve the Cynic

          "did u get the job after your pedantry?"

          I got an offer, but had a better one from somewhere else.

      2. Anonymous Coward
        Anonymous Coward

        My mother uses weird white appliances that are adorned with indecipherable symbols, instead of text that clearly says "detergent here" or "spin cycle". She also knows Pascal, on account of a 1980's OU maths degree, but doesn't get on terribly well with modern office suites.

    2. byrresheim
      Black Helicopters

      sorry but that should read:

      ... after using computers to fight fascism and give half of Europe to the Bolsheviks, we British then ...

      1. Anonymous Coward
        Anonymous Coward

        Re: sorry but that should read:

        I think you will it was Roosevelt and co. who gave half of Europe to Stalin. They knew how many American deaths there would be if they advanced past Berlin, and decided it was politically unacceptable to have to explain to American mothers why their sons were dead when Hitler would have lost the war anyway.

  13. Justice
    Thumb Up

    How I survive on 1.5kW?

    It would seem better than some reg hacks.


  14. Christian Berger

    Interresting from the developmental standpoint

    It's using dekatrons which are essentially counters. This hints that it may be based on counting registers, exactly as mechanical calculators did.

    In fact there were some desktop calculators like the ANITA which were based on the same principle.

    Essentially those calculators were advanced "adding" machines. You could only add to a register by making it count up a number of steps. Subtractions were made by adding complement numbers. So if you wanted to substract 1, you would add 999...999. You could also typically shift the number you wanted to add. So you could add a number times 10 for example. That makes multiplications fairly simple.

    In fact on the mechanical machines you often had to do those steps manually.

    I think this machine also shows an early approach to computing. It didn't matter that it was just as slow as a human. What mattered was that you could off load work. The computer, in the early days, was a monument to lazyness. People built computers because they couldn't be bothered to do manual computational work. It's much more fun to build a machine to do that sort of work for you, and much cooler, too. :)

    1. Dave 126 Silver badge

      Re: Interresting from the developmental standpoint

      > It's much more fun to build a machine to do that sort of work for you, and much cooler, too. :)

      I think Douglas Adams said that he was the sort of person who would rather spend two days writing a program that would automate a task that would have taken him half an hour to do himself.

  15. Zmodem

    britain brought american nukes because of a crap computer

    1. SkippyBing

      I'm fairly sure we built our own nukes, we just bought an American launch system for some of them.

    2. Mark Allen

      Baron Penney

      There wouldn't be a US bomb without assistance from the Brits. Check out Baron Penney. A key part of the original US design team.,_Baron_Penney

      Strange thing is I knew this guy when I was a kid. His wife used to babysit me and my sister at times. Or we'd go round for tea and cakes. I never knew his background until I saw a BBC documentary on the British Bomb. And there was Lady Penney talking about it... talk about jaw dropping!! Realising I personally knew someone involved with THE bomb certainly makes you think!! (Even more so now I read that Wiki article which shows Penney picked out the targets...)

    3. Hardwareguy

      Actually we just brought the rockets. we make ALL of America's nukes. Hah, funny how things turn around.

      1. Zmodem

        the documentries says britain brought rockets and warheads because of time and the new goverment canceled the projects or something along the lines

        1. SkippyBing

          You may be confusing warheads and MIRVS, I believe the nuclear non-proliferation pact prevents the US selling the UK nukes and they certainly hid behind it when we asked the information on the Manhattan project we'd been promised in exchange for taking part.

          Certainly your claim does raise the question of what the fuck AWE Aldermaston has been doing for the last 62 years...

          Although I wouldn't believe documentaries, they frequently get stuff wrong.

          1. Zmodem

            its a history documentry, the british warhead was`nt 100% stable or something, and the blue streak rocket was`nt finished, so they brought some american rockets, and part of the deal was the warheads that had to be included..

            trident nuclear weapons are american and made by lockhead or someone else

            either way, i am not bothered, blame it all on a computer that would take 2 months for some physics math, and another 2 month with 1 simple mistake

  16. CABVolunteer


    I find it surprising that nearly 1,000 thermionic valves and a load of lamps, plus all the energy required to power the relays, not to mention the losses in the power supply equipment, would require only 1.5kW. Sure it's not MW?

    1. PeterO

      Re: 1.5kW?

      Decatrons are "cold cathode" devices, so they produce very little heat (just like the orange neon indicators in mains switches).

    2. SteveastroUk

      Re: 1.5kW?

      I don't SEE much sign of people wilting from 1 megawatt being dissipated behind them.


    3. Anonymous Coward
      Anonymous Coward

      Re: 1.5kW?

      Someone else has noted that Dekatrons are cold cathode, but it's worth perhaps noting that a typical computer double triode consumes about 2.5 to 4 watts in the cathode(s) and about 2W in the anode circuit. A relay uses between about 300 and 600 mW. I am giving away my age here.

      So allowing about 5-6 double triodes per decade, you are still looking at maybe 30kW rather than megawatts - and the calculations would have been much faster. As the Flowers said to the Newman.

  17. JeffyPooh

    "Oldest Working Computer" - stop on exception

    Any of the elderly (*human*) "computers" still "working"?

    1. Scott Wheeler

      Re: "Oldest Working Computer" - stop on exception

      > Any of the elderly (*human*) "computers" still "working"?

      Probably not, but I know one who is in her mid 70s.

      1. Anonymous Coward
        Anonymous Coward

        Re: "Oldest Working Computer" - stop on exception

        Baroness Trumpington is around 90 and still attends the House of Lords, though I don't know if she ever did any manual computing at Bletchley.

  18. Primus Secundus Tertius Silver badge

    Slow division

    Ten seconds for a division in 1951.

    In 1967 I watched a big division take one second.

    I was using an IBM1620 machine to calculate PI to 300 places. Its architecture was binary coded decimal, so 300 correct places was almost as easy as 3. The algorithm involved dividing a 600 digit number by a 300 digit number, and it took about one second. The flashing lights stayed constant during the operation.

    1. Christian Berger

      Re: Slow division

      Well back then, the question was, whether to have a slow computer with few parts you can afford, or a fast computer with many parts which not only costs a lot more to build, but also to run.

      This computer was meant to be "affordable" replacing maybe a handful of human computers. It required next to no power and probably was quite reliable. It may have been cheap enough so everyone in the institution could just use it, without having to go through a lengthy permission process.

  19. ACx

    Is that Rodney Trotter?

  20. Matt Bryant Silver badge
    Thumb Up

    "......Power Consumption: 1.5kW

    Size: 2m high x 6m wide x 1m deep

    Weight: 2.5 tonnes

    Number of Dekatron counter tubes: 828

    Number of other valves: 131

    Number of relays: 480

    Number of contacts or relay switches: 7073

    Number of high speed relays: 26

    Number of lamps: 199

    Number of switches: 18......"

    Wow, someone actually has a worse spec work PC than I do!

    Joking aside, big congrats to the team that restored this beauty a second time.

  21. JCitizen
    Thumb Up

    This is a GREAT article!!!

    It was also fantastic to see the original scientists give their testimony to the history of computing! I imagine in the future, the US will not even be recognized as a contributor to this early technology, because we fall behind in the restoration of the original machines, or replica of such! Even though we did have a few first successes.

    I really have to hand to you Brits for keeping the history alive! KUDOs!!! This is SOOOOo KEWL!!! :)

  22. MrZoolook

    "Elderly giant takes 10 seconds to divide a number"

    But that's still faster then you're average web page load time on Sky Broadband!

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