CDI, or CD-Internet, was a technology developed by Sega in collaboration with several Japanese companies, including KDDI and NTT. It allowed Dreamcast owners to access the internet directly through their console, using a special CDI-enabled CD-ROM and a VMODEM (Visual MODEM) adapter. The VMODEM was a device that connected to the Dreamcast's VMU (Visual Memory Unit) and provided a dial-up internet connection.

The phrase refers to high-fidelity, self-booting game images (CDI format) hosted on the Internet Archive that are optimized to retain as much original data as possible despite the size constraints of standard CD-Rs . 💿 Key Components of This Content GD-ROM Information - CD Media World

Archive.org is the primary source for these files, often hosting curated sets from renowned preservationists. Here are some of the best places to look: 1. The Sega Dreamcast Indie Collection