ISO (disk image)
Also known as: .iso file, ISO image, how to open ISO, mount ISO
An ISO file is a disk image — an exact, single-file copy of an optical disc (CD/DVD) or its file system. You typically mount it as a virtual drive or extract its contents, rather than "installing" the ISO itself.
- Single-file image of an optical disc
- Mount as a virtual drive or extract — do not "install" it
- Uncompressed; can be several GB
Mount or extract, not install
An .iso captures a complete disc, including its folder layout, as one file. To use it you usually mount it: Windows 10/11 and macOS let you double-click an ISO to make it appear as a virtual disc you can browse. From there you run the installer inside, not the ISO itself.
Alternatively you can extract the contents with 7-Zip or Keka, or burn the ISO to a USB drive to create bootable installation media for an operating system.
The storage angle
ISO files are not compressed — they mirror a disc byte-for-byte, so a full DVD image is several gigabytes. Old game, OS, and installer ISOs are a common source of multi-gigabyte clutter in Downloads.
Once you have installed or extracted what you need, the ISO is usually safe to delete. Unlike a compressed archive, the data inside is already full-size, so mounting does not double your storage the way extracting does.