An Etsy store called 8BitMemory converts old NES games into external hard drives. They use Toshiba 2.5″ drives for the conversion. You can get a 500GB for $129.99, 750GB for $149.99, or a 1TB drive for $179.99. These drives are fully USB-powered. A Star Wars game is shown here, but many others are available. You can even request a specific game, if desired. Each hard drive comes with a USB cable and some come with the classic game sleeve to protect your drive.
