Ask HN: How does the software and hardware interaction work?

As a software developer, I realize that I have almost no idea about how the hardware actually works and how the interaction with software is achieved. I know, of course, some theory about computer architecture, but I still can't figure out how bits are represented in a hardware board or how a processor can do the things it does only using basic arithmetic operations.

Where could I learn about this stuff? Can you recommend any good course, videos or articles?