.CHD File Extension

CHD is one of several compression formats utilized in the retro gaming community. The compression method reduces the size of game data dumped from physical storage devices, such as arcade game machines, cartridges, and CD-ROMs.

Arcade machine hard disk CHD files

The CHD compression format was initially developed by The MAME Team to store arcade game disk images that could be emulated by MAME (Multiple Arcade Machine Emulator) software. These CHD files are used in conjunction with their corresponding game .ROM file to load an arcade game.

Some MAME CHD files have large file sizes because the hard disk contents they were created from were also large. Therefore, even though CHD files are compressed, they may still take up large amounts of disk space.

CD-ROM game data CHD files

Eventually, retro gamers began utilizing the CHD format to store the contents of games dumped from CD-ROM games for various consoles, such as Sega Dreamcast and 3DO. In these cases, the CHD files store the contents of the .CUE and .BIN files dumped from the CD-ROM game.

NOTE: You can create CHD files from dumped CUE files with the chdman command-line program developed by The MAME Team.

CHD files are not meant to be opened. Most emulators that support CHD files require you to place the CHD file in a directory that can be accessed by the emulator for it to load the contents in the CHD file. However, you should refer to your emulator's documentation for specific instructions.

To load a MAME arcade game - Place the CHD file in a directory that has the same name as the corresponding ROM's filename prefix. For example, if you have a ROM named mygame.zip, a CHD file named mygame.chd, and a ROM directory named Roms, you will typically store the ROM and CHD file in the following locations:

• /​Roms/​mygame.zip
• /​Roms/​mygame/​mygame.chd

NOTE: Other emulators require users to store all CHD files in one generic directory, often named Rom.