How to I install software from a .dmg file?
Written by Philip Roy A ".dmg" file is a disk image file. This is a series of files, an application or an application installer that is in a compressed format (to help with downloading off the net) that you can then 'mount' (load a temporary virtual disk) on your Mac to get the software from the disk image and onto your Mac permanently.
Let's take a look at installing the OmniWeb web browser. When you go to the Omni Group site, you'll download a ".dmg" file like the one you see here.
Double-click on the file and a window will appear, showing you the web browser application that you need to copy in to your "Applications" folder on your hard drive. The window may have hidden your "Applications" folder, so you may need to move it or (as in the example shown below) click in the top-right to expand the window.
Now we can see the application and your "Applications" folder. It is simply a matter of click and dragging (click and hold the mouse button down) on the OmniWeb application in the disk image, dragging it to the "Applications" folder and letting go (as shown below). You may get asked (if you are updating a program) if you want to replace an existing version.
Disk images have been around for some time. What you may not realise is that in the eyes of the computer, when you double-clicked on the ".dmg" file, you 'mounted' (loaded) a virtual disk or drive (a little like inserting a floppy disk in the days when we used to use those)....so the last thing you need to do is 'unmount' (eject) the disk image. You can see how easy it is to do that in the image below. The ".dmg" file could then be deleted if you want.
Variation 1 - An application that needs installing
Not all disk images contain an application that you drag and drop. Some disk images contain an installer and should clearly indicate this. In the example below, you don't drag this application into your "Applications" folder at all...instead you double-click on it, follow the installation procedure (which will put a program into your "Applications" folder itself) and then unmount the disk image.
Variation 2 - Clever dragging and dropping
Some recent disk images have made the whole process even easier by creating a link from the disk image to your "Applications" folder for you. All you have to do is drag and drop within the disk image itself. This might seem a bit confusing, but is very clever. In the Skype example you can see below, dragging Skype into their neat looking "Applications" folder will in fact install the program straight on to your Mac. Just unmount the disk image afterwards and you're done.
Disk image files are very easy to use once you get used to them, but some people find them a little confusing...mostly for two reasons:
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Some people mount a disk image and then try to use the application on the disk image from there, rather than dragging a copy of the application to their "Applications" folder. In most instances this is not a good idea.
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Some people forget they haven't made a copy of the application in their "Applications" folder, then find it hard to eject the disk image or wonder why the application has disappeared next time they start their computer. If you're having this problem, you probably didn't install correctly the first time.
Last Updated Tuesday, 30 November 1999
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