An ISO image is an archive file (a.k.a. isk image) of an optical disc using a conventional ISO format that is supported by many software vendors. ISO image files typically have a file extension of .ISO but Mac OS X ISO images often have the extension ".CDR". The name "ISO" is taken from the ISO 9660 file system used with CD-ROM media but the term ISO image can refer to any optical disc image, even a UDF image.