BIS is leftover ROM after the OS is loaded. It will not be wiped even with a Hard Reset and is a good place to put an Executable (.exe) type of Back Up, such as that created by Sprite Backup.
HERE's how I have my Sprite Backup configured.
Not good for some programs, as ROM has a limited number of Writes. It's a large number (100,000 or so), but some programs update continuously and that latge number could get eaten up pretty quickly.