What is ISO?

An ISO image is an archive file that contains the complete contents and structure of an optical disc, including the file system itself. Unlike regular archive formats, ISO images preserve the exact sector layout, making them perfect for creating bootable discs and virtual drives.

ISO images follow the ISO 9660 standard, which defines the file system used on CD-ROMs. Modern ISO images often include extensions like Joliet (long filenames for Windows), Rock Ridge (Unix permissions), and UDF (for DVDs and Blu-rays).

Did you know? The Linux community distributes millions of ISO images daily. Ubuntu alone has been downloaded over 100 million times as an ISO image!

History

The ISO 9660 standard was published in 1988 by the International Organization for Standardization to create a universal file system for CD-ROMs. It was based on the High Sierra Format developed by a consortium of computer companies.

Key Milestones

  • 1986: High Sierra Format proposed for CD-ROM standardization
  • 1988: ISO 9660 standard officially published
  • 1995: Joliet extension adds Unicode support for Windows
  • 1996: Rock Ridge extension adds Unix file attributes
  • 2000: UDF becomes standard for DVDs
  • 2006: UDF 2.50 adds support for Blu-ray discs

Key Features

Core Capabilities

  • Exact Disc Copy: Sector-by-sector replication of optical media
  • Bootable Support: Can contain bootable system images
  • Virtual Mounting: Can be mounted as virtual drives
  • Multi-Session: Supports multiple recording sessions
  • Cross-Platform: Compatible with all major operating systems
  • Large Capacity: Supports CD (700 MB) to Blu-ray (128 GB)

Common Use Cases

Operating System Installation

Windows, Linux, and macOS installation media

Game Distribution

Physical game backups and retro gaming

Virtual Machines

VM deployment and testing environments

System Recovery

Bootable recovery and diagnostic tools

Advantages

  • Exact copy of original disc including boot sectors
  • Universal compatibility across all platforms
  • Can be mounted without burning to physical disc
  • Preserves complete disc structure and metadata
  • Standard format for OS distribution
  • Supported by all virtualization software

Disadvantages

  • No compression (files can be very large)
  • Cannot be modified after creation
  • Limited to optical disc size constraints
  • Requires special software to create
  • Not suitable for regular file storage

Technical Information

Format Specifications

Specification Details
File Extension .iso
MIME Type application/x-iso9660-image
Standard ISO 9660:1988
File System ISO 9660, Joliet, Rock Ridge, UDF
Compression None (uncompressed)
Maximum Size 8 TB (theoretical)

Common Tools

  • Windows: ImgBurn, Rufus, Windows Disc Image Burner
  • macOS: Disk Utility, dd command
  • Linux: mkisofs, genisoimage, dd, Brasero