Non-Digital Computers
This is the last installment of my many-part series on computers. Last time we used the notion of a Turing machine to define what a computer is. We discovered something surprising: that not all computers need to be digital, or even electronic! A computer can be mechanical, made of dominoes, or even just a rules system in a card game.
To give you of a flavor of how inclusive the definition of a computer really is, I’ll now give you a whirlwind tour of some notable examples of non-digital computers.
The Antikythera Mechanism
In April of 1900, Greek sponge divers found a shipwreck off the coast of Antikythera. They found a lot of artifacts aboard the ship, but by far the most valuable piece was a device made of bronze gears. This is the Antikythera mechanism, and it’s not only the oldest known complex gear mechanism, but the oldest known purpose-built computer.
The Antikythera mechanism seems to have been made around 100 BC. It seems to have been designed to predict the motions of stars and other celestial objects. Scientists and historians are still studying it, but some replicas have been attempted.
To learn more, check out the Antikythera Mechanism Research Project’s website and their promotional video:
Charles Babbage’s Analytical Engine
In 1837, inspired by his successful creation of a mechanical calculator (the difference engine—see the title image of last week’s post), polymath and all around amazing dude Charles Babbage designed a fully programmable mechanical computer called the analytical engine. This is widely regarded as the first fully programmable computer.
The mathematician (and countess) Ada Lovelace corresponded with Babbage regarding his analytical engine and she is credited with much of its theoretical underpinnings. She also designed the first and only algorithm for the device, making her the world’s first computer programmer.
Unfortunately, because of the huge scale of the analytical engine and the precision with which the parts needed to be machined, Babbage never finished constructing it.
Tide-Predicting Machines
In 1872, physicist Lord Kelvin developed a mechanical computer to predict the tides.
The Enigma Machine
In World War II, the Axis powers encoded and decoded their military orders using an electromechanical computer called an Enigma machine. Enigma was so sophisticated that the code could be changed by programming the machine. Some historians credit the Allied victory to the help of Alan Turing and the world’s first true digital computer, Colossus, which allowed the Allies to crack Enigma’s famously difficult code.
For more information, check out Numberphile’s excellent video on the device.
Other Examples
Some more, less historically interesting examples include:
- It’s possible to make arbitrarily good approximations of purpose-built Turing machines using dominoes. They’ll never be as good as a real Turing machine, though, because they can only write to a bit in memory once (by knocking down a domino). Check out this awesome video, again by Numberphile.
- In the card game Magic the Gathering, one can construct a situation where, just by following the rules, the players become components in a universal Turing machine. The “mathematical” proof is here.
- It’s possible to build a fully working computer using the physics engine of the video game Minecraft. Here’s one guy’s computer. And here’s a tutorial on how to make your own.
Any I Missed?
If you know of any cool non-digital computers I missed, let me know in the comments!
Related Reading
This is the sixth article in my multi-part series on computing. These are the other parts:
- In this article, I describe the basics of Boolean logic, starting with truth tables.
- In this article, I describe how to make composite logical statements using Boolean logic.
- In this article, I introduce the triode vacuum tube and describe how it works.
- In this article, I show how to use triodes to make logic gates.
- In this article, I explain how to build computer memory.
- In this article, I explain how a Turing machine works.
- In this article, I use the idea of a Turing machine to try and nail down what exactly a computer is.
EDIT: Cracked.com covers this topic!
I’m a big fan of the comedy website Cracked.com. They often teach you something in a pretty entertaining way. So imagine my surprise when I discovered this morning that they ran an article covering the same idea as this one, but with some really awesome examples of pre-microchip computers that I’d never heard about!
It’s a beautiful article by the awesome ex-physicist Luke McKinney. You can check out his blog here: lukemckinney.net
Without further ado, here’s the article:
http://www.cracked.com/blog/4-amazing-computers-made-before-microchips-existed/
The inner workings of pre-1976 pinball machines probably count as electromechanical computers. I owned one once, and got to see how logic gates were implemented with EM relays. These things were the size they were because they were filled with miles and miles of copper wire and dozens of these relays. Modern pinball machines that use circuit boards and chips to do the same thing are mostly empty inside, although they use the same size cabinet.
Yes, you can make a computer this way, but it would weigh a ton and consume a lot of power. It took three people to get the thing out of my house when my wife was tired of looking at it.