World’s Oldest Functioning Digital Computer Reminds Us Of A Telephone Exchange

This is the WHICH, the Wolverhampton Instrument for Teaching Computing from Harwell. It is the oldest functioning digital computer and thanks to a lengthy restoration process you can go and see it in person at The National Museum of Computing in Milton Keynes (Northwest of London in the UK).

The system was first put into operation in 1951. It’s function is both familiar and foreign. First off, it uses decimal rather than binary for its calculations. And instead of transistors it uses electromechanical switches like are found in older automatic telephone exchanges. This makes for very noisy and slow operation. User input is taken from strips of paper with holes punched in them. As data is accumulated it is shown in the registers using decatrons (which have since become popular in hobby projects). Luckily we can get a look at this in the BBC story about the WITCH.

According to the eLinux page on the device, it was disassembled and put into storage from 1997 until 2009. At that point it was loaned to the museum and has been undergoing cleaning, reassembly, and repair ever since.

[Thanks David]

28 thoughts on “World’s Oldest Functioning Digital Computer Reminds Us Of A Telephone Exchange

    1. ^^^ This, all of those parts are very common (and many still working) in the UK telephone network. The rebuild of Colossus used many parts donated by BT as they decommissioned equipment.

  1. “This is the WHICH” “Wolverhampton Instrument for Teaching Computing from Harwell” ” the BBC story about the WITCH.”

    Am I mistaken, or should it be WITCH the first time as well? It’s an easy typo to make!

  2. Ha! So this was installed in my local tech when I was 4 years of age eh? It sort of makes me feel privileged…

    Alas a few months later I was on a boat bound for Australia where my local tech had it’s first computer installed, when, lets see, was it last year? ;-)

  3. The memory stores on this computer use Dekatron glow transfer counting tubes to store each digit. There are two types used, the GC10B (the ones that glow orange), which are common, and the GC10A (the ones that glow purple), which are frightfully rare. Back when the team first started to restore this device, they caused a stir in the tube collector community by putting out a request looking for a donation of 800 or so GC10A tubes, wholly unaware that most tube collectors assumed there were less than 800 GC10A tubes left in the entire world, period. Fortunately the GC10A and GC10B are largely interchangeable; I strongly suspect they are keeping most of the ample stock of GC10A’s they found with the computer in storage and using much more common GC10Bs wherever possible.

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