The conversion process itself typically involves command-line tools, most notably the chdman utility bundled with MAME. A basic conversion command— chdman extractcd -i game.chd -o game.iso —extracts the primary data track from the CHD and writes it as an ISO. However, this operation discards any subchannel data, audio tracks in Red Book format, and multisession information. For pure data discs (e.g., software installers, game data CDs without CD-DA audio), the resulting ISO behaves identically to the original. But for mixed-mode discs, the converted ISO will lose background music or copy protection, making it unsuitable for accurate emulation.
You want to burn the game back to a physical CD or DVD.
is a lossless compression format originally developed for MAME (Multiple Arcade Machine Emulator). It is designed to reduce the massive file sizes of CD and DVD ROMs. chd to iso
: Use a similar syntax or a shell script ( .sh ): ./chdman extractdvd -i input.chd -o output.iso Method 3: Alternative Tools
Converting these CHDs will produce a standard ISO file. This works perfectly with tools like ImgBurn or Dolphin Emulator. For pure data discs (e
Conversely, converting ISO to CHD is equally common— chdman createcd -i game.iso -o game.chd —and is recommended for long-term storage. The CHD format’s compression and checksumming (SHA-1, CRC-32) guard against bit rot and allow verification of data integrity. Many archiving communities, such as Redump or No-Intro, encourage CHD for distribution because it reduces bandwidth and storage costs without data loss—provided the original disc lacked critical subchannel data.
Why would someone perform such a conversion despite these limitations? Practicality often outweighs purity. Many operating systems can mount ISO files natively without third-party drivers, whereas CHD requires specialized tools or emulators. Burning software universally accepts ISO for physical disc creation. Additionally, some older emulators or virtual machines lack CHD support. Thus, converting to ISO trades structural completeness for compatibility. A common workflow is to maintain a master archive in CHD format for preservation and generate ISO copies on demand for active use. is a lossless compression format originally developed for
Since CHDman is command-line only, community developers have created Graphical User Interfaces (GUIs) to make the process "drag-and-drop."
: A web-based version that runs in your browser, requiring no local installation. Why convert back to ISO?
Note: Use extractdvd for DVD-based games (like PS2) and extractcd for CD-based games (like PS1 or Sega Saturn) .
It is important to understand that the output format depends on the original media: