The x86 bios firmware is raw binary of 16-bit real mode machine code. Upon CPU reset, it starts executing at 0xffff0 address, which is 16 bytes below 1MiB. This address space is typically mapped to the ROM containing the BIOS.

This video showcases a few interesting things: qemu isa-debugcon device, qemu monitor, rizin editor (radare2 fork), and coreboot.

Related reading: https://wiki.gentoo.org/wiki/System_Initialization_of_Intel_x86_with_BIOS_Firmware