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We know that Charles Babbage designed the first Turing-complete mechanical machine - the Analytical Engine - in the 1800s, but it was never actually built (not yet anyway).

In recent history, at least one mechanical Turing machine has been built. (This example is in fact a Universal Turing Machine, albeit with finite storage space.) But was this the first one, or are there earlier examples?

What was the first mechanical Turing-complete machine constructed, who built it and when?


Edit: By mechanical, I mean no electronics are used.

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  • I don't think that before WW2, Turing considered building a mechanical Turing machine. IMHO, Turing machine was then a theoretical construction. Building one mechanically is fun, but is not efficient. Mechanical computing machines existed since Pascal (XVIIth century, France) and where more efficient doing useful computations (additions & multiplications ...) Feb 6, 2016 at 6:43
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    Nobody wanted that. Tabulators were for the accounting and censuses, analog devices solved differential equations and were better as gun/bomb/torpedo sights (cheaper and smaller). Feb 6, 2016 at 12:20
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    The first working freely programmable computer was maybe Konrad Zuse's Z1 Feb 6, 2016 at 14:42

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There is a good chance that Jim MacArthur's machine (mentioned in the question) is in fact the first.

Here are the contenders I am aware of:

The Analytical Engine. As joeytwiddle points out, it has not yet been implemented.

Konrad Zuse's Z1. It had I/O, memory, and an arithmetic unit, but it did not have branching. So, not Turing complete.

Relay-based machines. The linked SE question lists a number of computers that, it says, were mainly relay-based. You could say these were not electronic, but rather electromechanical. They are full-fledged computers, but I am inclined not to count them as fully mechanical.

In 1978, Danny Hillis and Bryan Silverman designed and built a tic-tac-toe-playing machine made from Tinkertoys. But it was not fully programmable, being more an encoding of the full game tree of tic-tac-toe.

It should be possible to construct a machine that runs under steam power (or is fully belt-driven anyway with no internal electricity required), uses punch cards for bulk storage, and can do general computer tasks like calculation and text processing. But it would be a significant endeavor and would get a lot of publicity. The Analytical Engine is a bit like that. I think a project to make something even fancier would be an unlikely boondoggle.

All of that said, I was not familiar with MacArthur's machine until I read this question, so it's possible another hobbyist has beaten MarArthur to the punch.

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