DMG (Apple disk image)
Also known as: .dmg file, how to open dmg, mount dmg, Mac disk image
A DMG is Apple’s disk-image format, used mainly to distribute Mac apps. You double-click it to mount a virtual drive, drag the app to Applications, then eject and delete the .dmg — you do not "install" the DMG itself.
- Apple disk image, mainly for Mac app installs
- Mount, drag app to Applications, then eject
- Safe to delete the .dmg from Downloads after
How a DMG install works
Double-clicking a .dmg mounts it as a disc that appears on the desktop and in Finder’s sidebar. Most show an app icon and an Applications shortcut: you drag the app onto Applications to copy it in, then eject the mounted image.
The DMG is just the delivery container, not the installed app. After the app is in Applications, the .dmg in your Downloads folder is no longer needed and can be deleted.
The storage angle
DMG files often pile up in Downloads — every app you ever installed may have left one behind, each holding a full copy of the app. Clearing old .dmg files is a quick, safe win, since the real app already lives in Applications.
DMGs can be compressed or read-only, and can hold disk images or backups too, but for most people they are simply the file you open once to install a Mac app and then discard.