Video game emulation dawned in the 1990s and exploded during the 2000s. Players can find and download image files that contain game data from cartridges and play them using emulators, software that emulates console hardware such as the NES and PlayStation. Those image files are known as ROMs, short for “read-only memory.” Publishers stress that ROMs are illegal; you are, after all, downloading old games for free rather than paying for them through active digital services such as Nintendo’s Virtual Console.