Arcade game disk image used by some MAME (Multiple Arcade Machine Emulator) emulator games; stores a compressed version of the entire contents of an arcade machine's hard disk; used in conjunction with a game ROM to load the game.
To load a MAME arcade game, you typically need to place the CHD file in a directory has the same name as the ROM's filename prefix (some emulators use a single generic directory for all CHD files). For example, for a ROM with the filename mygame.zip, a CHD file named mygame.chd, and a ROM directory Roms, emulators commonly use the following convention:
Some CHD files are large in size due to the original size of the arcade hard disk. Therefore, even though CHD files are compressed, they may still require large amounts of disk space.