If you are into retro gaming emulation, you have likely encountered the (Compressed Hunks of Data) file format. While CHD is excellent for saving hard drive space, many emulators, modding tools, and burning software still require the standard ISO format.
While CHD offers better compression (about 10% better than CSO), some hardware or older versions of emulators (like older PPSSPP builds) may not support it, requiring a return to the standard ISO format. chd to iso