CHD stands for Compressed Hunks of Data. It is a compressed archive format primarily used for storing data from arcade games, particularly ROM images and CD-ROM images. The CHD format was developed by MAME (Multiple Arcade Machine Emulator) developers to efficiently store large game data files, reducing their size without significant loss of information. The compression algorithms used in CHD are lossless, ensuring that the original data can be perfectly reconstructed when the archive is decompressed. This is crucial for preserving the integrity of game data. CHD files are commonly used in emulators and arcade game preservation projects. The format supports multiple compression methods, allowing for a balance between compression ratio and decompression speed. CHD files are often used to store data from optical media, such as CD-ROMs and DVDs, used in arcade games. The CHD format has become a standard for archiving and distributing arcade game data, facilitating the preservation and accessibility of these games for future generations.