How are hard disks read from and written to?

[hardware beginner]

How does it happen on the motherboard? I searched a lot and couldn't find a detailed explanation that I could understand. I click a file on my computer, this is retrieved from the hard disk and then displayed on my screen. From what I've found it's some sort of interaction where the keyboard sends an interrupt signal and somehow this sends an address to the CPU and the CPU sends that to the hard drive, and RAM is involved. I can't find information that lays out step by step what happens.

I also couldn't find a proper definition of external data bus. Which part of the motherboard is it? Does it refer to all the traces outside the CPU or what?

 

[popatim]

thisis beyond the scope of this sub forum. Basically windows is software. all software runs on the cpu and resides in the ram. The software interprets you mouse clicks turning them into commands that the CPU sends to the southbridge (which controls the drives amungst other things) which then calls in file from the hdd and sends it back to the cpu to load into ram. the software is signalled that the file is available and then proceed to process it whether that be open the file for reading, proccess it for playback, or execute it (run it)

The external data bus is the the data bus thats outside of the processor itself. Some of the traces ont he motherbd are the external data bus, some are the address bus, some are pci & pcie... lots of buses!