What is a .iso file?
ISO 9660 Disc Image · Disk image · ISO / ECMA · 1988
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.
What opens 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.
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
Open a .iso file step by step
- Confirm the file really is a .iso. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with File Explorer (mount) or 7-Zip.
- On Mac, use Disk Utility or double-click to mount.
- On Linux, try mount command or GNOME Disks.
- Still stuck? Convert the .iso to Burn to disc or USB, which opens more widely.
Why can't I open my .iso file?
Almost always because no installed app understands ISO. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .iso at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .iso file
You can convert a .iso file to Burn to disc or USB.
An ISO is written to media rather than converted. Rufus on Windows and the built-in Disk Utility on a Mac write it to a USB stick. To just read the contents, 7-Zip opens an ISO like an archive.
What is the .iso file signature (magic bytes)?
A .iso file carries the hex bytes 43 44 30 30 31 at offset 32769, which read as CD001 in ASCII. Programs identify ISO by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for ISO. For a full breakdown, see the ISO 9660 file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 43 44 30 30 31 | 32769 | CD001 | 'CD001' at offset 0x8001 |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .iso file?
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.
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
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