First, thanks for replying to me here and pointing out the error in my title. I want to try and use a portable disk-drive to play PS2 and Dreamcast games so I've updated it accordingly. As for why it's really for the same reason someone would want to play an NES game on the original cartridge, even if they're using a Retron 5 or some other device that employs emulation. It's what I grew up with and, since the purpose of this device is in part to relive that nostalgia, I figure it's worth trying to make work like this. I've heard elsewhere that, though PS2 games due to the raspberry pi's architecture are out of the question, Dreamcast and PS1 disks may still work so I'll post an update once I get the components and can test it out. Thank you all again for the replies.
