Boot protocols are very uninspiring, arcane knowledge and understanding it does not bring any advantages (unless you want to write bootloaders). Especially dealing with legacy BIOS boot sequence, which is essentially a backwards compatibility emulation layer implemented in the firmware.

It's not like home computers of the 1980s where you'd look at the processor data sheet how the CPU actually boots (which address the program counter starts from, what's the initial machine state, etc).

By far the easiest way to get started in x86 bare metal programming is using the Multiboot header, which is supported by bootloaders (like Grub) and emulators (like QEMU). And you can use GDB for debugging.

Using UEFI is more involved to get started. The initial setup is more involved (you need UEFI headers and libs, etc), the build process is more complex (UEFI images are "Windows" PE executables) and attaching a debugger is not as easy as with a Multiboot-ELF image. UEFI "boot services" provide some nice things that may be helpful to get memory maps and CPU hierarchy so you don't need to go through the hassle of parsing EBDA and MP and ACPI tables.

The legacy BIOS boot protocol is "easy" to get started with (nasm -f bin mykernel.asm), but you have to deal with arcane stuff (like floppy drive BIOS routines, A20 lines), you don't get a debugger. This is by far the worst way to get started. It's not really "doing it from scratch", instead of using a proper bootloader you need to deal with a really bad bootloader implemented in your PC firmware.

The biggest advantage is that your kernel images are a bootable, debuggable ELF binary.

The emphasis being on "debuggable", you can easily plug in GDB to QEMU and use a proper debugger with your bare metal projects. Using GDB is much better than using the built-in debugging facilities of QEMU or Bochs. You can get the source view, set breakpoints and do everything you normally do in a debugger. In QEMU/Bochs built-in debuggers you have no source view and can only inspect memory and registers - not variables with symbolic names.

Here's some examples and documentation on building a debuggable ELF image for bare metal project, which I contributed to someone else's project:

https://github.com/Overv/MineAssemble/commit/56e317a28d069f4...

The more people keep using BIOS, the more likely it will stay around. IMHO UEFI is a bloated mess compared to BIOS, so I very much hope the latter will continue to live.

httpss://github.com/ReturnInfinity/Pure64