.iso File — ISO Disc Image

ISO files are disc image files that contain an exact sector-by-sector copy of an optical disc (CD, DVD, or Blu-ray), stored as a single file. Named after the ISO 9660 filesystem standard for CD-ROMs, ISO images preserve the complete disc structure including the filesystem, boot records, and all file data. ISO files are used for distributing operating system installation media (Windows, Linux distributions, macOS recovery), software installers, game discs, and archival copies of optical media. Most modern operating systems can mount ISO files directly as virtual drives without burning them to physical discs. ISO images are typically created using disc ripping software or the dd command on Unix systems. The format supports various filesystem standards including ISO 9660 (with Joliet and Rock Ridge extensions for long filenames), UDF (Universal Disc Format) for DVDs and Blu-rays, and hybrid images that combine multiple filesystem types. ISO files are bootable when they contain the appropriate boot records, making them essential for creating bootable USB drives with tools like Rufus, Etcher, or dd.