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Antikythera, Babbage, and The WITCH

05/09/2013 @ 7:30 pm - 11:00 pm

On this occasion, I will be taking you back to the days before binary was considered to be a neat idea. Back to the days before silicon. Back to the days when Computation was a great engineering feat of imagination and ingenuity. Back to the Future! dawn of:

The programmable digital calculator!


Roll up, roll up, for a video and commentary presentation spanning a few thousand years in three simple steps to the pre-dawning of our digital era and of how whirry things can count. (The digital era was actually a bit earlier but that’s Ultra Top Secret! 🙁 )

We are also honoured to have a special visit on the night by three Daleks Dekatrons.


This THURSDAY at our old haunt at Fellows, Morton and Clayton. (No football! Food promised.)

  • 7:30pm meet and food;
  • 8:00pm-ish talk and discussions and anything and everything Linux.


All at:

Fellows Morton and Clayton
54 Canal Street
Nottingham, NG1 7EH
Telephone: 0115 9506795

latitude = 52.948615
longitude = -1.148431
Google map

Good beer. Food served up until 8pm.


All welcome. (Just ask the friendly bar staff if lost 😉 )



dekatron counting


This talk was a presentation of (by the power of YouTube):

  • From under the sea from 200 BCE:
    Computer Over 2000 Years Old
  • TV-hype and romanticism aside, this is truly a remarkable mechanism that embodied all the then known science of astronomy along with the astrology beliefs of the Greeks of that time. All by the hand of the genius of Archimedes who lived nearby?
    Virtual Reconstruction of the Antikythera Mechanism (by M. Wright & M. Vicentini)
  • One view of how the device may have originally looked and operated:
    2000-year-old computer recreated
  • This very geekie reconstruction highlights nicely the additional fantastic development beyond that of using the teeth on gear wheels for counting years and days. There is the use of a differential gear to add a fractional input. This is all thousands of years before common use and over two thousand years before such use in mechanical analogue computers! Phenomenal!
    Lego Antikythera Mechanism
  • Jumping forward to the Victorian 1840’s, possibly the first reuse of gears for mechanical counting and computation is with the designs by Babbage. Here, one of his designs has finally seen implementation some one-and-a-half centuries later, concisely presented by Doron Swade whilst located at the Science Museum, London:
    Babbage’s Difference Engine No. 2

    Notable aspects of the design include: decimal counting of the register stacks; fixed point calculation precision to 31 decimal places; a cam mechanism to implement “microcode” control of the hardware functions; and vector pipeline operation producing one result per four cycles.

  • We took a brief diversion to a little heard computing pioneer who in some ways paralleled the sort of work done by our Tommy Flowers (belatedly of Colossus fame). They both suffered similar restrictions imposed by wartime secrecy
    Konrad Zuse’s computing machine Z3
  • And thence onwards to utilizing newly developed new technology of the day, we fast-forwarded to the 1950’s and the first use of the decimal counting Dekatron:
    The reboot of the Harwell Dekatron / WITCH computer, the world’s oldest working [electronic] computer

    Notable aspects of the WITCH are that the dekatrons count in tens by the position of a gas discharge glow pulsed sequentially around 10 electrodes, hence forming an electronic analogue of ten teeth on a gearwheel as was used by Babbage and (presumably) Archimedes many years previously; a huge innovation was that the dekatrons stored the decimal digit aswell as counting a decimal count, greatly reducing the required physical component count; the dekatrons also gave a visual readout for their held number (again, just like a physical gearwheel). Hence, you got a lot of multifunctionality for your one vacuum tube! Also note that the WITCH can run a program sequence from any of punched paper tape, a program stored in the banks of dekatrons, or both. A program loop can be made by gluing together the ends of a punched tape sequence to physically form an instruction sequence loop!

    Note the present tense. After all, it is still working! As our group saw glowing and clanking during our latest visit to Bletchley Park and TNMOC.

    Sadly, since the YouTube video was made, Ted Cooke-Yarborough (righthand most in the video) has passed on.

    Dekatrons can be viewed as integrating into one compact device the operation of multiple thermionic valves and associated passive components, thus offering a great saving in space and component costs. Also consequently offering greater reliability.

Since the dekatron, we have subsequently developed the use of transistors and binary operation. We now have semiconductor chips orchestrating the operation of billions of transistors… But that is for another talk/presentation… 😉



7:30 pm - 11:00 pm
Event Category:


Fellows Morton and Clayton
54 Canal Street
Nottingham, NG1 7EH United Kingdom
+ Google Map
0115 9506795

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