An ISO image is an archive file (disk image) of an optical disc using a conventional ISO (International Organization for Standardization) format. ISO image files typically have a file extension of .ISO. The name “ISO” comes from the ISO 9660 file system used with CD-ROM or DVD media, but an ISO image can also contain UDF file system because UDF is backward-compatible to ISO 9660. You can mount an ISO file or images via the loop device under Linux. It is possible to specify transfer functions (for encryption/decryption or other purposes) using loop device.