ISO File (Disc Image)

An ISO file (disc image) is a single file that contains the complete contents and file-system structure of a CD, DVD or Blu-ray disc, usually following the ISO 9660 or UDF standards. The .iso extension is the usual convention.

Why it matters

Most operating systems, including Linux distributions and Windows, are downloaded as ISO files. You can write one to a USB drive or disc to install the system, or open it as a virtual drive without any physical media. Virtual machine software also accepts ISO files as a virtual DVD, which makes testing a new system simple.

Example

Downloading ubuntu-24.04-desktop-amd64.iso, you can verify it against the published checksum:

sha256sum ubuntu-24.04-desktop-amd64.iso

If the hash matches the one on the download page, the file arrived intact. On Windows and macOS you can double-click an ISO to mount it as a drive and browse the files inside.

Common mistakes

• Copying the ISO onto a USB stick as an ordinary file. It will not boot; the image must be written with a tool that makes the stick bootable.
• Skipping checksum verification, which hides corrupted or tampered downloads.
• Downloading ISOs from unofficial mirrors, which can bundle malware.

Related

• Bootable USB
• Operating system
• Virtual machine
• Mount

This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.