Realize that I am NOT asking about how MMIO (memory mapped input/output) is set up, but asking how it is mapped, I.e, what maps it exactly? Not what is mapped to what, I can Google a memory map for that.
What I want to know is, such as once you first power on the computer, what exactly "maps" the memory, or how does that work?
Basically, what sets up the memory or "maps" it for certain purposes?
I had originally thought it was boot firmware, like BIOS or EFI/UEFI, but another user on another site told me it had to do with a memory controller. Is that true?
But how, if in more detail, if not too much to ask? Thanks very much to any who clarify!