Colossus and the WITCH at The National Museum of Computing

The lovely Steve Colgan and I had a great visit to The National Museum of Computing last week. We were given a fab tour of all the museum by the very knowledgable Kevin Murrell. Just check out a few of the fabulous computing history artefacts on display there. Its like a trip down memory lane and beyond for anyone who has been involved in computing.

We saw the Harwell Dekatron or WITCH, the oldest working computer in the world.

What a beautiful machine, with a fabulously relaxing sound as it runs. Here’s a Vine short video of it running:

What do you think? Isn’t it fabulous? πŸ™‚


All of the machines at the museum have been restored with tender loving care by an army of dedicated volunteers.

It is a treasure trove of computing history. The piece de resistance at The National Museum of Computing has to be Tony Sale and his team’s rebuild of Colossus: the world’s first programmable digital computer. It is an absolute masterpiece. Invented and built during WW2 by genius post office engineer Tommy Flowers at Dollis Hill in London to mechanise the codebreaking process.



I really enjoyed getting a close up look at the valves. They are so beautiful.



Here’s a link to a short Vine video of Colossus running:
Love it!

The National Museum of Computing is based at Bletchley Park near Milton Keynes, north of London. The fast train from Euston Station in London takes only 36 minutes, its a great place for a day trip. It is usually open on Thursday, Saturday and Sunday afternoons from 12-4pm. Check here for details before you travel:

It would be great to hear about other computing history museums from around the world. Do tell me about your favourite computing museum with a link below in the comments. I’d love to hear about computer history museums from around the world:) I’ve visited the Computer History Museum in Mountain View, California, several times, which is great too. I absolutely loved their working model of Babbage’s Difference Engine. Unfortunately I can’t find a pic or video of it, so here’s a pic of their fab geek badges instead


It’s so important for us to look after and showcase our computing heritage. Computers and computing have changed, and are changing, rapidly. Look at the way 8Mgb was stored in the first photo above in the 1970s, and think about the size of 8Mgb storage on a mobile phone today. What a massive difference!

Do visit TNMOC if you get the chance, and if you would like to help them with their work make a donation through their website. All donations are doubled by matched funding from a generous sponsor.


  1. The computer section of the Science Museum in London is also very good – Babbage engines, Pascal calculator, Curta calculator… before you even get to the Hollerith hole-punch and digital stuff.

  2. Some additional info:

    we have a wiki page dedicate to collecting information about the WITCH along with restoration projects at

    the wiki page includes many reference links and documenation including the recently restored copy of an article on the design of the WITCH from 1951:

    we also have lists and datasheets for many of the original components:

    we also have an online emulator for the WITCH under developement at

    if you are interested in discussing the educational aspects of the WITCH or other antique/historic computers, you can visit the #retro-computing channel on

  3. Hi Sue, Thanks for your latest post about TNMOC – love the photos and the point you make about the size of 8Mgb data storage ‘then and now’. Somewhere I have a souvenir from the 70s when I was at City University in London working on ICL1900s. It’s a 1K memory board of woven ferrite core, each tiny polo of core (about 2mm diameter) is threaded on 4 wires I think … the whole board is about 6 x 4 inches.

    What I really converted was something John Cooper, a colleague at City, had – a Nickel delay line from the Ferranti Pegasus that City had used. Super object with valves and a great loop of wire with little amplifiers on each end about 9 x 12 inches … all for remembering one string of bits. I guess each delay line ‘stored’ a byte of data … but I’m guessing there. John later rebuilt a Pegasus for the Science Museum / BCS or someone.

    On a sadder, serious note, did you hear any more about the dispute between TNMOC and BP while you were up here (I live in Woburn Sands just down the road from Bletchley)? News seems to spluttered out every now and then … then it all goes quiet until the next time. Is one or other of the parties playing a waiting game hoping for the other lot to wither-up and die? It does all seem very silly and it must be upsetting for those people who, like myself, are so pleased that both enterprises are in existence.

    Best wishes


    Sent from my iPad


    1. Thanks Simon, isn’t it crazy how memory/size have changed?

      No, I didn’t hear any more. The military looking fence between the two sites upsets me, and I’m sure many others. It’s such a shame 😩

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