Don't know if this belongs here, but I recently bought a portable music/video player which is also able to play Famicom, Sega Genesis, Game Boy and Game Boy Advance games. Brand is generic, "Portable 311 player", but I was wondering how they emulate the games, since it's obvious no real NES/Genesis/GBA hardware is included. Is any kind of information about how these things emulate games on the internet? Specially considering how many NES games have problems: Burgertime kicks me to the game selection screen after losing one life, Zombie Nation doesn't works, Antartic Adventure has corrupted graphics, The Goonies doesn't starts at all, etc.
Also, the selection of built-in games is questionable: it includes Japanese Dragon quest games which are... in Japanese... and it also has such shit like "Baseball" and "Mario is missing", but the games can be easily changed using the included USB cable.