When you download software that uses disk images, the idea is that you'll mount the image, copy the application to your hard drive (typically to the /Applications folder) and then dismount and discard the disk image. You're not meant to run applications from them. That brings me to the most important thing about disk images. So if you wonder 'where did that folder with my Application disappear to?' it may be that the disk image unmounted. When you reboot your computer, the disk image automatically unmounts. Either drag it to your trash can or Control-click (right-click) the volume and choose Eject from the contextual pop-up menu. When you're done using the disk image, you can eject it. Copy items from the disk image by dragging them to your desktop or to your folders. You can then double click this virtual drive itself to open its contents in a new Finder window. This usually looks like a white hard drive. The image mounts as a new volume on your desk top. To open a disk image, you just double click on it.

They store files in a way that acts like one of these data storage devices. Disk images are a kind of virtual disk-like a CD or DVD or even a hard drive. If you've ever downloaded a DMG file from a website, you've dealt with a disk image.

Download mac disk image