In an x86-P6 based computer system, does PC BIOS map the memory prior to startup?

[Big Tunda]

Does the onboard firmware (BIOS) map the memory on power up before OS lookup or Power On Self Test?

This is arbitrary since every BIOS is different.

Would the process vary based on firmware, microarchitecture, or any other manufacturing process?

I know about CPUID for memory map info and such, but I am asking specifically about the mapping process, not the information.

EXTRA: This would mean that if the firmware mapped the memory (and not manufacturers of the motherboard, i.e., unchangeable) that would mean that memory can be mapped manually by editing BIOS instructions, or "re-programming"/updating the chip.

In old computer systems, like the NES, Gameboy, Segas, etc., consoles did not use firmware (ok, some did, but most didn't back then), so all of the memory was set and permanent for specific purposes, and not changeable by firmware, if the firmware is what's mapping the memory map in the first place.