An ISO image is a single archive file that replicates the entire contents and file system structure of an optical disc, such as a CD, DVD, or Blu-ray. Named after the ISO 9660 file system standard, it preserves directory hierarchy, metadata, and—if applicable—boot information. Although originally designed for optical media, ISO images remain widely used for digital software distribution, particularly for:
- Operating system installation media (e.g., Windows, Linux distributions).
- Bootable recovery environments and firmware updates.
- Virtual machines and containerized environments, where ISO files serve as mountable volumes.
- Offline deployment and air-gapped system installations.
Modern tools and platforms can mount ISO images as virtual drives, extract their contents, or write them to bootable USB drives using utilities such as Rufus, balenaEtcher, or the macOS Terminal (dd).
Despite the decline of physical optical discs, ISO images remain a standard, platform-agnostic format for distributing complete system images and pre-configured software environments.