This looks like exactly what I've been hoping to find after taking an OS course last semester! Thank you very much for sharing this link!

That's pretty impressive. Unfortunately the BIOS is still required for getting a map of physical memory...

Funny thing is that they both do basically the same thing, except one is done all in assembly and the other in C.

I would have liked this post to actually discuss the things that a bootloader is meant to do, like switching to 32-bit protected mode and loading the next block of code from the disk.

Yep, instead of looping over an interrupt just use "rep movsb" between the data segment and display memory.

No, none of the description in this guide applies to UEFI. The UEFI firmware loads its bootloader as a PE binary from a FAT filesystem, not a binary blob from sector 0, and the CPU is already in 32- or 64-bit mode. The interface for calling firmware routines is also completely different.

This is a decent equivalent guide for UEFI: http://www.rodsbooks.com/efi-programming/hello.html