It's a bit more complex. Beyond using a bespoke ~1GB GD-ROM format that normal optical drives can't read, the discs did AFAIK have copy protection of the "wobbl

It's a bit more complex. Beyond using a bespoke ~1GB GD-ROM format that normal optical drives can't read, the discs did AFAIK have copy protection of the "wobbly track" variety. So even if you have a GD-Recordable drive and media, you couldn't just copy the games. (Although if you have a GD-R drive you almost certainly had the dev tools to run unprotected games anyway). Unfortunately they wanted a way to add Dreamcast content to music CDs ("MIL-CD"), which led to a massive holes in the security that meant it would happily boot off CD-Rs. I guess they didn't want to tie record companies to Sega's own duplicators so the CDs don't have any direct copy protection. Instead CD programs are "encrypted" (unlike GD-ROM games) and the disc drive turned off after initial load. Naturally the encryption / scrambling was figured out, and people figured out how to turn the drive back on[1]. Thus fun with piracy and homebrew. Late in the production run they removed the MIL-CD stuff entirely, although the vast majority of systems out there would've been built by then. (Sorry if I've got any details wrong). [1] Plus a bonus that the boot sector could contain unchecked extra code that made "self booting" pirate games possible.