And this is how GD-ROMs got ripped. Broadband adapter and the shoot out the data over Ethernet
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Interestingly, for a long time there were no publicly available tools for or docs on dumping GD-ROMs. New releases from Echelon and Kalisto would appear promptly, so there was obviously a way, but you could only partake in the rampant piracy by downloading the (occasionally-massaged to fit on a CD) disc images online.
A lot of discussion in the (tbf probably quite young and inexperienced) community was around how this was possible. A popular theory/rumor at the time was that they were using CD drives with modified firmware, for example.
This probably also helped keep the piracy amd homebrew scenes fairly well separated on the Dreamcast, as there was a lot of info and examples around running your own code. This is in contrast to eg. the Xbox scene, which was in many ways the equally vibrant successor to the DC scene, but where piracy and homebrew seemed much more intertwined. Not least because all the homebrew binaries were built using the off-limits Microsoft SDK, so you had to go to some shady FTP site via links found on IRC to download them.
Another alternative that was reasonably-priced for a short while was the Japan-exclusive "LAN Adapter", which was in lower demand because it was only officially supported by the Dreamcast web browser app and was only 10Mbps instead of 10/100.