Chicago Boyz

What Are Chicago Boyz Readers Reading?

Recommended Photo Store
Buy Through Our Amazon Link or Banner to Support This Blog
  •   Enter your email to be notified of new posts:
  •   Problem? Question?
  •   Contact Authors:

  • CB Twitter Feed
  • Lex's Tweets
  • Jonathan's Tweets
  • Blog Posts (RSS 2.0)
  • Blog Posts (Atom 0.3)
  • Incoming Links
  • Recent Comments

    • Loading...
  • Authors

  • Notable Discussions

  • Recent Posts

  • Blogroll

  • Categories

  • Archives

  • Cool Retrotech: a New Oldest Computer

    Posted by David Foster on January 24th, 2013 (All posts by )

    The world’s oldest functioning computer  is now the WITCH, aka the Harwell Dekatron Computer, recently resorted to operating condition in Britain. It is also, almost certainly, the world’s slowest functioning computer.

    The WITCH, built at Britain’s Atomic Energy Research Establishment,  was designed circa 1949 and completed in 1951. Circuits are comprised of dekatrons..a type of electron tube with an inherent count-to-ten capability..and ordinary telephone relays. The machine can store 40 eight-digit numbers, and while it can operate in stored-program mode, it was more normal to execute programs directly from punched paper tape. A “loop” when operating in this mode was an actual physical loop, with the ends of the tape glued together.

    This computer was designed for reliability rather than blazing (by the standards of the time) speed, and it was so slow that a human could keep up with it for a limited period of time—but after half an hour or so the human would have to drop out, exhausted, while the machine plowed on, “utterly relentless.” I’d guess that the WITCH..taking into account its ability to operate unattended..could do as much computation as a human group of 5-10 people. Despite the machine’s slowness, the staff at Harwell found it useful, and it continued in use there until 1957, when it was given to Wolverhampton Polytechnic…which is where it got its current name, the Wolverhampton Instrument for Teaching Computer from Harwell. There it supported research and teaching until 1973. It was rescued from storage a few years ago and restored by volunteer efforts. It is now on display at Bletchley Park, the WWII center for codebreaking.

    The restored WITCH displaces the previous oldest-working-computer champion, the Ferranti Pegasus.

    WITCH video here.

    Related post about the reconstruction of another early British computer, the EDSAC.


    3 Responses to “Cool Retrotech: a New Oldest Computer”

    1. Bill Brandt Says:

      That is amazing….

      About 1974 I worked with a Burroughs B-700 – an early minicomputer with performance that would be laughable today. But it was light years ahead of the Harwell Dekatron

    2. dearieme Says:

      All histories of computing written before the Ultra revelations of the mid 70s must have been unavoidably wrong. Do any of their errors survive in modern accounts? I’m thinking more of popular accounts than scholarly ones.

    3. Mike K Says:

      An interesting story. In 1959, we used to do the calculations on a Marchant calculator before the program went into the IBM 650. The Marchant was probably faster than the Dekatron.

    Leave a Reply

    Comments Policy:  By commenting here you acknowledge that you have read the Chicago Boyz blog Comments Policy, which is posted under the comment entry box below, and agree to its terms.

    A real-time preview of your comment will appear under the comment entry box below.

    Comments Policy

    Chicago Boyz values reader contributions and invites you to comment as long as you accept a few stipulations:

    1) Chicago Boyz authors tend to share a broad outlook on issues but there is no party or company line. Each of us decides what to write and how to respond to comments on his own posts. Occasionally one or another of us will delete a comment as off-topic, excessively rude or otherwise unproductive. You may think that we deleted your comment unjustly, and you may be right, but it is usually best if you can accept it and move on.

    2) If you post a comment and it doesn't show up it was probably blocked by our spam filter. We batch-delete spam comments, typically in the morning. If you email us promptly at we may be able to retrieve and publish your comment.

    3) You may use common HTML tags (italic, bold, etc.). Please use the "href" tag to post long URLs. The spam filter tends to block comments that contain multiple URLs. If you want to post multiple URLs you should either spread them across multiple comments or email us so that we can make sure that your comment gets posted.

    4) This blog is private property. The First Amendment does not apply. We have no obligation to publish your comments, follow your instructions or indulge your arguments. If you are unwilling to operate within these loose constraints you should probably start your own blog and leave us alone.

    5) Comments made on the Chicago Boyz blog are solely the responsibility of the commenter. No comment on any post on Chicago Boyz is to be taken as a statement from or by any contributor to Chicago Boyz, the Chicago Boyz blog, its administrators or owners. Chicago Boyz and its contributors, administrators and owners, by permitting comments, do not thereby endorse any claim or opinion or statement made by any commenter, nor do they represent that any claim or statement made in any comment is true. Further, Chicago Boyz and its contributors, administrators and owners expressly reject and disclaim any association with any comment which suggests any threat of bodily harm to any person, including without limitation any elected official.

    6) Commenters may not post content that infringes intellectual property rights. Comments that violate this rule are subject to deletion or editing to remove the infringing content. Commenters who repeatedly violate this rule may be banned from further commenting on Chicago Boyz. See our DMCA policy for more information.