How does the code/software - hardware interaction takes place?

Question

What is the core concept behind the code-hardware interaction?
I know that the codes we write causes the voltage fluctuations in the circuit and the processor and that is the reason behind for the data being processed; but I don't know the core concept behind it and how it happens.

Answer 1

There are few layers between your program and hardware normally. Brief description on how for example memory works https://lwn.net/Articles/250967/
and this brief description is not really short.
So in most cases when you program you need to know how the OS will interact with your program.