An ISO image is a disk image file that contains an exact, sector-by-sector representation of the contents and structure of an optical disc, such as a CD, DVD, or Blu-ray disc. ISO images are most commonly created using the ISO 9660 file system standard, though they may also include extensions such as Joliet or Rock Ridge to support longer filenames, Unicode characters, and additional metadata.
ISO images preserve the original disc’s directory layout, file system metadata, and boot information, allowing them to function as faithful replicas of physical media. As a result, an ISO image can be mounted by an operating system and accessed like a physical disc or written back to optical media or a USB drive.
ISO images are widely used for the distribution of operating systems, software installers, and recovery tools, particularly when bootable media is required. Because the format encapsulates the entire disc structure in a single file, it ensures consistency, integrity, and ease of distribution across different platforms.