This uses the int 15, E820 extension of fairly modern bioses which requires a 32-bit processor and a BIOS that supports that function. It works on an old Pentium-120 I have and bochs, so any x86 later than 1995 might be able to boot this.
A minor tweak in the code using a different interrupt and the elimination of a couple of 32-bit instructions will make this code usable on any x86 with a BIOS.
So, without further ado, I give you Ultimate 0.0.1 with source and a usable floppy image (which is really just nasm output assembled to a 1.44mb image of zeros).
Here's my roadmap:
1) write a more generic bootloader using int 10h, AH=C7h
2) finish C code to take information from bootloader and generate a memory map
3) use int 13h to load the driver interface code I've written, load subsequent sectors into memory, and jump to the beginning of the loaded code.