Binary — anything at all, with just two states
Counting with eight light bulbs
Board 1 · Tap a bulb to turn it on
All a computer knows is on and off. Tap a bulb. Sweep your finger across and several come on at once.
Press +1 several times. The bulbs come on from the right, and then at some point they all go off at once and one to the left comes on.
Board 2 · Make this number
There is one trick. Start with the big bulbs, and never go over.
Board 3 · Letters are written in bulbs too
Every character has a number the whole world has agreed on. Type anything. Korean letters work too.
The English alphabet has small numbers, so 8 bulbs are enough. Korean letters have large numbers and need 16. That is why Korean text so often came out as garbage on old computers: a machine that knew only the 8-bulb agreement had met a 16-bulb letter.
The story behind the switches
What you just did by hand is written up in these pieces. They read far more easily after you have tried it.
Each extra place doubles how many values it can hold. Eight give 256; thirty-three are enough to count everyone on Earth. The reason computers use only two states is not mathematics but sturdiness — with only on and off, the electricity can wobble a good deal and the answer is still right.