And then even before BIOS/EFI is Intel’s ME or AMD’s PSP. And when control is handed over to the BIOS/EFI, the processor is pretending to be an 8086-era process

And then even before BIOS/EFI is Intel’s ME or AMD’s PSP. And when control is handed over to the BIOS/EFI, the processor is pretending to be an 8086-era processor running in “Real Mode” (16 bit). The BIOS/EFI have to tell the processor to stop pretending (switch to “Protected” (32 bit) or “Long Mode” (64 bit)), do their things - and in the case of the BIOS, switch back to Real Mode - and then hand control over to the OS. It’s layers and layers of complexity all the way down. It’s astounding how much technical debt there is in these machines, and yet they still work.