Eli5: Computers can calculate based on instructions. But how do you teach computers what does it mean to add something, multiply, divide, or perform any other operation?

Question

Edit: Most of the answers here are wonderful and spot on.

For those who interpreted it differently due to my incorrect and brief phrasing, by ‘teaching’ I meant how does the computer get to know what it has to do when we want it to perform arithmetic operations (upon seeing the operators)?

And how does it do it? Like how does it ‘add’ stuff the same way humans do and give results which make sense to us mathematically? What exactly is going on inside?

Thanks for all the helpful explanations on programming, switches, circuits, logic gates, and the links!

In: 583

Answer 1

There’s a fun explanation from the remembrance of earths past also known as the three body problem, a book not the famous conundrum. It explains how you could create a manual computer using humans that make decisions based on the actions of the humans in front of them.

The example in the book shows 3 soldiers each given a flag. The middle soldier is told only to raise his flag if both soldiers on his sides raise theirs. This of course emulates an AND gate which is a type of transistor arrangement where if a high input is on both inputs the output will become high as well.

This scene in the book highlights really well that there’s not really any understanding at all, it’s simply a matter of arranging components that react in certain ways in long enough chains that complexity emerges…

By the way you know where else components arrange themselves in a sort of chain reaction that looks like conscious understanding but actually ends up being entirely based on an individual design? Your body 🙂