I am working on a story idea where a character in a medieval world develops a rudimentary computer. It is made of simple building blocks similar to the flip-flop and and/nor gates of digital logic. It is built with wood and iron, and operated by a water wheel. I imagine that its computing power is roughly similar to the first machines used in WWII, such as the Turing machine and the Enigma. With it, she can perform computations far beyond the abilities of humans. But I'm stuck on how it could be useful. All I have so far is...

  • Predict various astronomical events with greater accuracy
  • Encode messages that can't be broken by hand

There must be something else that a conputer, hundreds of years ahead of its time, would enable this character to do. What am I missing?

EDIT: this is different than the suggested duplicate in my opinion. That question asks what it would need to be feasible; this asks what one could do with such technology. Further, it's a different sort of machine than an abacus.

  • $\begingroup$ Hi @nuggethead, you'd better use the Search option before putting questions here, duplicates are a reason for close. A first attempt gave me this list: worldbuilding.stackexchange.com/search?q=medieval+computer $\endgroup$
    – Goodies
    Commented Jan 9, 2022 at 12:49
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    $\begingroup$ (1) The Turing machine is a mathematical object, not some sort of physical device. (2) The Enigma was not a computer in any meaningful sense of the word computer. (3) There were lots of computing devices made before WW2. For example, slide rules, naval gun laying directors and, most importantly for the history of computing, tabulators and unit record equipment in general. (4) No, you cannot make them with medieval technology. $\endgroup$
    – AlexP
    Commented Jan 9, 2022 at 13:48
  • $\begingroup$ Remember, assignment of "Duplicate" refers to the answers of the dupe addressing the issues, not the question being identical. $\endgroup$ Commented Jan 9, 2022 at 14:11
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    $\begingroup$ The problem with this idea is the assumption that flip-flops, etc. could be made in wood and iron and be useful. Binary / digital arithmetic was useful only because the electronics ran so fast. With wood and iron driven by a water wheel, the computing would be so slow that analog computing would work better. $\endgroup$
    – David R
    Commented Jan 9, 2022 at 15:04
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    $\begingroup$ I think that this question should be reopened. Indeed the answers to the proposed duplicate contain some examples of medieval computational devices, but only a limited number of these. The answers also do not focus on the usage of the technology which is the main problem here. The purpose of the WB.SE is to help world builders with their specific problems. And I believe it would be more helpful to the OP if they could get answers addressing their specific hurdles. $\endgroup$
    – Otkin
    Commented Jan 9, 2022 at 19:24

1 Answer 1


Until mechanical and electronic calculators became practical and common, bulk calculations used to be done in specialist counting houses by experts using abaci. In fact, an expert using an abacus could perform calculations as quickly as we might use a calculator.

So, if this mechanical computer could process calculations faster than an expert with an abacus, it would be a valuable business tool.


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