Disk image
Also known as: what is a disk image, disk image file, IMG file
A disk image is a single file that mirrors the entire contents of a disk or volume — its file system, structure, and data. Common types include ISO (discs), DMG (macOS), and IMG. You mount or write a disk image rather than just extracting files from it.
- A file that mirrors a whole disk or volume
- ISO, DMG, and IMG are the common types
- Mounted or written, not just "extracted"
A whole disk in one file
Unlike an archive, which bundles a set of files, a disk image is a faithful copy of an entire volume — including its file system. That lets it represent a bootable installer, a backup of a drive, or the exact contents of a CD/DVD.
You typically mount a disk image so it appears as a virtual drive (the case with ISO and DMG), or write it to physical media like a USB stick to recreate the original disk, for example when installing an operating system.
Common formats and the storage angle
The most common types are ISO (optical discs), DMG (Apple’s format, mostly Mac app installs), and IMG (a generic raw image). Some, like DMG, can be compressed; others, like a raw IMG, are full-size byte-for-byte copies.
Because images can mirror a large drive, the files get big fast. Old installer images and one-off backups are a frequent source of multi-gigabyte clutter — delete them once the install or restore is done and the data lives elsewhere.