An A78 file is a game ROM file used by Atari 7800 emulators, which can play Atari 7800 games as if they were run on the original system. It contains an exact copy of game data from the original game cartridge, which is used by an emulator to play the game.
A78 files are used by a variety of emulators to play older Atari games on computers. Some Atari 7800 emulators that can open A78 files include Emu7800, ProSystem Emulator, MESS, and OpenEmu.
Atari 7800 is a video game console released in 1986 that replaced the Atari 5200. Some Atari 7800 game titles include Centipede, Dig Dug, Ms. Pac-Man, and Desert Falcon.