What are Nintendo DS BIOS used for?

A Nintendo DS BIOS is used for the purpose of running Nintendo DS games off a cartridge on the console itself. It allows the software to interact with the console. It is also needed to make the only working NDS emulator (No$GBA) read the roms so they can be played on a computer. The BIOS can be ripped using any device that allows custom content to be played on the DS once special code is run. The BIOS cannot be freely distributed in any way, because it is software owned by Nintendo. In short, the BIOS is used for reading the games...