What is a Computer? - Part I

We all think we know what a computer is. It's a box in a room full of blinking lights. It's the PC or laptop at home. Most people even understand that a mobile phone is also a computer. These are facts that we grew up with and understand without needing to think too much about it. But in actual fact, there are many ways to create a computer without using any electronics nor indeed electricity. Ultimately we will see that computation can even take place spontaneously in nature!

Humankind's journey with computers truly started with a paper written around 85 years ago by Alan Turing. Interestingly, the purpose of this paper was not to invent the concept of a computer but rather to provide a mathematical proof of something called the https://en.wikipedia.org/wiki/Entscheidungsproblem. However, in order to create the proof, Turing invented the formal concept of computation by machine - the so-called Turing Machine.

A Turing machine is an abstract model of a computer that manipulates symbols on an infinite strip of tape according to a table of rules. One can 'run' programs on such machines by following the rules and manually marking the tape with the symbols using a pen. Turing showed that this machine was universal i.e. it could perform any calculation that any other form of machine could perform.

To see a Turing machine in action, you can watch the video below. This was a program I created to simulate a calculation on such a machine. The particular program we are running adds two numbers together. You can see the two numbers are shown in binary on the left hand send of the tape. (1011 and 1010). After a lot of shuffling around and marking and erasing symbols, we are left with the binary result on the right hand end of the tape (10101). Note that this exact same computation could be performed by you with a piece of tape, a pencil and an eraser!

You can easily see the impracticality of this machine. It took 377 steps just to add two numbers together, but with enough time, and tape, Turing proved that any calculation can be performed.

If you want a little more info on how CA's work, have a look here in the section 'Music Improvisation' :- https://joeamgaines.wixsite.com/morevoices/post/games-through-the-ages

The Turing Machine gives us a very valuable conceptual computer and also shows us that a computer doesn't require to be implemented with either electronics or even electricity.

There are in fact other interesting, counter-intuitive, ways of creating computers. For example, dominoes. Yes, with dominoes it is possible to create a computer!

In order to see how, we first need to understand the concept of a logic gate. A modern Intel processor implements billions of such gates in silicon in order to create a complete computer but again, the concept of a logic gate doesn't require electronics.

An example of a logic gate is the OR gate :-

If input A is 'on' OR input 'B' is on, the the output of the OR gate is 'on' too. We normally use one to represent 'on' and zero to represent 'off'.

Back to dominoes. Could we represent this gate using dominoes? Yes. In fact it is very simple and you can do it yourself. Take 3 dominoes. Stand one up to represent the 'out'.

Now stand the two other dominoes side by side but slightly behind the 'out' domino.

Now if you push domino 'A' OR domino 'B' then the 'out' domino will fall, representing a one. If you don't push either, then nothing happens - 'out' remains as zero!

So you have just implemented an OR gate using dominoes. It turns out you can implement all the other logic gates required to construct a full computer!

Take a look at this - the 10,000 domino computer :- https://www.youtube.com/watch?v=OpLU__bhu2w

So now we have seen two examples of non-computer computers! In Part II, we take a look at another very important example, one that leads us to the idea of spontaneous computation in nature!