I'm not sure i really understand. I think the efi replaces the bios, and it's a firmware developed in C.I guess we do not need a traditional MBR. I think that need GPT disk format, but i would like to know if it's possible to make another custom method
However, I have the impression that the EFI only recognizes the PE format.
In a couple of words, UEFI firmware replaces BIOS but provides BIOS emulation for compatibility purposes. It understands PE32+ file format for executable images and FAT file systems. You can add support for other file formats and file systems with the help drivers (which should be in PE file format). Boot flow will be as follows: firmware boots your custom boot loader from a bootable device. The boot loader loads additional drivers (for example, to provide ext file systems support) and continues with boot process (loads kernel from ext fs).
Is it possible to start in BIOS with good screen resolution ?
Not sure if I understand your question, but you don’t have control over what video mode BIOS sets up before your bootloader is started, the same applies to BIOS emulation in UEFI (since it’s emulation, remember?).
So, if you choose to write a BIOS bootloader, you have a text-mode (03h, AFAIR). After that you can either deal with good old modes, you can try VESA modes (if supported by emulaion layer) or you can load your OS, which in turn loads video drivers and then uses any resolution your video adapter supports.
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