The CD-ROM filesystem provides transparent access to CD-ROM media, so you can treat CD-ROM filesystems as though they were POSIX filesystems. This transparency allows processes to operate on CD-ROM files without any special knowledge or work on their part.
The fs-cd.so manager implements the ISO 9660 standard as well as a number of extensions, including Rock Ridge (RRIP), Joliet (Microsoft), and multisession (Kodak Photo CD, enhanced audio).