How does a Kernel/OS communicate with Devices on the motherboard

Question

I think I understand the basic principles of OS, kernel, BIOS, and drivers. But I can't finish understanding how all of these components communicate.

My doubt comes from how the OS ultimately communicates with a device connected to the motherboard. I understand that the OS must have a driver to communicate with said device. But ultimately a driver is Machine Code, a set of instructions that the CPU can understand.

But how can this set of instructions, which only has to do with the CPU's architecture, communicate with something out of that architecture? I've read that the BIOS might map some register that will be read/written by the device. But that arose another doubt, is the BIOS standardized? Or are each OS or Driver adapted to each kind of BIOS and the mapping of those special registers to communicate with the devices connected to the motherboard?

I cant seem to put my finger on these topic, maybe i cant formulate a well crafted search on Google. Further reading material on those subjects would be greatly appreciated.

Answer 1

Broad question, broad answer: The instructions a CPU (or GPU etc) executes are actualized as changes in potential or current in circuits; similarly devices on the mother board (or the CPU or the GPU) receive instructions as changes in potential or current in circuits. When the CPU "sends a signal" to a device, it's changing the electrical flow in a circuits that connect it to the device - generally through intermediary circuits that manage signaling flow.