What is a .iso file? (ISO)

An ISO is a complete image of an optical disc in a single file. It is how operating systems and software are distributed for download, and you can mount it like a virtual drive or burn it back to a real disc or USB stick.

What is a .iso file used for?

An ISO captures every byte of a CD, DVD or installer, so it is a faithful, bootable copy you can use without the physical disc.

Windows and macOS can mount an ISO as a drive with a double-click. To make bootable install media, you write the ISO to a USB stick with a tool like Rufus or balenaEtcher.

Because it is a full image, an ISO can be large, matching the size of the disc it represents.

How to open a .iso file

The .iso format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .iso file.

Windows

File Explorer (mount)
7-Zip
Rufus (to USB)

macOS

Disk Utility
double-click to mount

Linux

mount command
GNOME Disks
Archive Manager

Web

Not applicable; download and mount

How to convert a .iso file

You can convert a .iso file to Burn to disc or USB using a conversion tool or the export menu of an app that opens it.

.iso file signature (magic bytes)

Programs recognise a .iso file by the bytes at the start of the file, not by its name. These are the signatures for ISO. For a full breakdown, see the ISO file signature page.

Hex signature	Offset	Note
43 44 30 30 31	32769	'CD001' at offset 0x8001

See the full magic-numbers reference for every format.

Frequently asked questions

What is a .iso file?

How do I open an ISO file?

On Windows and Mac, double-click to mount it as a virtual drive. To install an operating system, write the ISO to a USB stick with Rufus or balenaEtcher.

Related formats

Sources

Details on this page were checked against authoritative references:

Wikipedia: ISO 9660