While many people do use ISO images for creating backups of their optical disc, ISO images these days are used primarily for distributing large programs and operating systems, because it allows all the files to be contained in one easily downloadable file. Most operating systems (and many utilities) also allow you to mount an ISO image as a virtual disc, in which case all your apps treat it as if a real optical disc were inserted. The idea behind ISO images is that you can archive an exact digital copy of a disc, and then later use that image to burn a new disc that’s in turn an exact copy of the original. They are a sector-by-sector copy of the disc, and no compression is used. You can think of an ISO image as a complete copy of everything stored on a physical optical disc like CD, DVD, or Blu-ray disc-including the file system itself. The name ISO was taken from the name of the file system used by optical media, which is usually ISO 9660.
