ISO (ISO 9660 Disc Image)
ISO is a disc image format that contains an exact sector-by-sector copy of an optical disc (CD, DVD, or Blu-ray). It preserves the complete filesystem structure and is used for distributing operating system installers, software, and creating bootable media.
MIME Type
application/x-iso9660-image
Type
Binary
Compression
Lossless
Advantages
- + Exact byte-for-byte copy of disc contents
- + Mountable as a virtual drive on all modern operating systems
- + Standard format for OS distribution (Linux, Windows)
- + Supports bootable media through El Torito specification
Disadvantages
- − No compression — file size equals disc size
- − Not practical for general-purpose file archiving
- − Large file sizes (650 MB for CD, 4.7 GB for DVD)
When to Use .ISO
Use ISO for distributing bootable operating system installers, archiving optical discs, and creating virtual disc images.
Technical Details
An ISO file contains raw disc sectors (typically 2048 bytes each) with the ISO 9660 filesystem. It may include El Torito boot records for creating bootable media. The image can be mounted directly as a virtual drive.
History
The ISO 9660 filesystem standard was published in 1988 for CD-ROM data. The .iso file extension became the standard for disc images in the 1990s. Extensions like Joliet (long filenames) and UDF (DVDs) expanded its use.