This is the grey area. It is open-source software that modifies hardware you own. However, downloading ROMs or ISO files of games you do not physically own is copyright infringement. The modding community’s golden rule: Only back up games you personally own.
: New games are placed in a specific "transfer" folder on the USB; Project Eris automatically moves and organizes them upon the next boot. Project Eris and the PlayStation Classic as a "Retro Box" ps1 classic project eris