The Software Series: DMG Files

The Software Series: DMG Files
Mac Tip #290/23-May-2007

One very common way to distribute software is with .dmg files (Disk Images). Most of the software I’ve downloaded lately uses the .dmg format, one example being the fine free web browser called Opera.

Opera uses DMG files

After you download Opera, for example, you see a file with a name like this: Opera_9.21_Setup.dmg.

Double click that .dmg file, agree to the License terms, and a new window opens on screen with two icons: the red O of Opera.app and a folder labelled Applications.

Note the curvy black arrow at bottom left of the Applications folder icon. That indicates that this icon is an alias of the real Applications folder.

Some disk images don’t include that alias. If you strike one that doesn’t then just drag the application you’re installing on to the Applications folder in the sidebar of your Finder window, or open a new window for Applications and drag the program into that window.

A pale grey arrow between the red O and the folder icon on the disk image suggests you should you drag the O onto the Applications folder alias. This copies Opera.app to your Applications folder.

If you already have a version of Opera an alert will appear to warn you and asking you to Replace the older version or Stop the copy. The alert may also include the words “older” or “newer” if the version you already have is older or newer than the one you’re trying to copy into Applications.

Once the copy is complete you can eject the disk image and, if you like, delete the file Opera_9.21_Setup.dmg. You no longer need either.

One common mistake is to try to run the software directly from the disk image instead of first copying it to the Applications folder. While this may sometimes work, at other times it just creates problems. Always drag the software into the Applications folder, and then run the software from there.

Next week: Other formats.