Files with the extension .A78 are ROM image files for use with the 'Atari 7800' system. .A78 files and ROM image files in general are copies of the video game data held on a read-only memory chip (such as a video game cartridge).
.A78 Rom files are used in conjunction with Atari 7800 emulation software, this allows users to emulate the experience of using the older atari system on a newer computer or console.
The Atari 7800 was a popular video games console released back in 1986
by the Atari corporation.