How Sega fit more game data onto a Dreamcast disc
A Dreamcast GD-ROM was not simply a CD with a different label. It used a denser recording format, giving it roughly 1.2 gigabytes of capacity—substantially more than a standard CD-ROM, which typically held around 650–700 megabytes. That extra room mattered as games grew more ambitious, with larger worlds, more detailed graphics, and extensive audio or video.
The disc’s layout also helped distinguish it from an ordinary CD. A GD-ROM included a small, standard-density region and a much larger high-density region. The Dreamcast’s drive could read the latter; a conventional CD drive could not access the game data there in the usual way.
More capacity, and a hurdle for copying
Sega’s proprietary format raised the bar for unauthorized duplication because common CD burners and readers were built for standard CDs, not GD-ROMs. A copied disc therefore was not as straightforward as making a bit-for-bit copy of an ordinary game CD.
But the format was a hurdle, not an unbreakable lock. The Dreamcast could also run software from recordable CDs through a separate compatibility feature, and that eventually gave unauthorized copies a route onto the system. The larger disc bought developers room and made casual copying harder, but it could not guarantee that games would remain exclusive to factory-pressed discs.
