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 are specific circuits to do things like add, multiply, and divide. The instructions we give to the computer are telling it to use those circuits. The computer holds numbers in something called a register, so when you give the computer instructions, it pulls the number either from an input or memory, puts it in a register, and then it runs the operation on that register and puts the result in a new register.

The registers are just a series of pins that either have a voltage or don’t. These are the 1s and 0s.