The Dreamcast bootsector (commonly named IP.BIN) is placed on a GD-ROM or a MIL-CD in the first 16 sectors of the data track from which the Dreamcast is booting. It contains information about the software on the disc, including Region protection, as well as the code that displays the Sega copyright screen, and bootstrapping code.
Originally a bootsector was lifted from Dreamcast games to boot homebrew software, but technically using this copyrighted code was illegal. Homebrew coder LiENUS rewrote the IP.BIN file, replacing as much as possible with free code. The only code that remains in this now-standard IP.BIN is Sega's copyright screen code, which is required to be unmodified in order for the disc to boot (the system checks it against a copy of the code held within the BIOS ROM). It is believed that using this last bit of code is legal due to the legal precedent set by Sega v. Accolade.