ce magazine march 2019 issue

Maybe the first thing you would think of is a mechanical computer, like the
Babbage Difference Engine:
While it’s a beautiful piece of engineering, it’s actually not a computer. It’s a
calculator. Charles Babbage did design a mechanical computer, called the analytical
engine. It’s never been built, because it would take up an entire room and be
extremely expensive. I don’t think the Romans could have built the analytical
engine or other purely mechanical computer because of the tolerances required. I
don’t know much about their manufacturing abilities, but I know they didn’t do a
lot of it and imported most things. I couldn’t find the tolerances needed for the
Harvard Mark I, an electromechanical computer, but I’m hesitant to believe that
they could have built that either. It’s hard to know how precise manufacturing
techniques were back then, but one of the best clues we have is the Antikythera
mechanism. It uses hand cut gears that are surprisingly precise, but still probably
not good enough for a mechanical computer. Small inaccuracies in the gear trains
would add up, and this is evident in the Antikythera mechanism. It would be even
more pronounced in a room sized contraption and would almost certainly prevent
any useful calculations from being performed.
If the Romans couldn’t do it mechanically, they would have needed a
semiconductor. When most people think of semiconductors, they think of clean
rooms and millions of dollars of machinery. However, that kind of equipment is
only needed for high performance semiconductors used in modern integrated
circuits with high speed, high efficiency switching. It turns out that
naturally occurring semiconductors are actually quite common. Minerals like
zincite, bornite, and carborundum will work. However, the best mineral to use is
lead sulfide, AKA galena. It be used without any modification directly after mining.
It’s got a band gap of about 0.4 eV. Ancient societies knew all about galena, and the
Egyptians used it as makeup.
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