Disk Images for New Users

by Ryan, ryan@smalldog.com

The standard downloaded software distribution medium used by OS X is called a Disk Image (.dmg). Disk images are, in my opinion, the best way to package software for distribution over the Internet to a Mac. However, many people do not grasp the concept of disk images.

When you download a new software application for your Mac, it will most likely come as a disk image. This will look like a little hard drive on a piece of paper and will have the extension ”.dmg” amended to the end of the filename. You double click this icon, and it will mount the Disk Image on your desktop, it will normally look like a white disk drive icon and will automatically open. Your computer treats the mounted Disk Image as if it were an external hard-drive or USB flash drive.

Now, drag the software program’s icon from disk image window and place it in your Applications folder. This is the full extent of the installation process, but I often see people running software programs like Firefox directly from its Disk Image. They try to throw away the Disk Image and it will not let them because it is in use. When you are done with the Disk Image, unmount it by throwing it in the trash and then throw out its related .dmg file.

You can also create Disk Images of your software CDs and other non-startup disks by selecting them in the Disk Utility program located in Macintosh HD/Applications/Utilities. Once selected in the Disk Utility application, click “New” from the toolbar and select “Disk Image from device”. One benefit is that you can mount the Disk Image and run your games that require a disk without the annoyance of actually carrying the disks with you—provided the game doesn’t include protection against this. Another use is to make backups of your disks and then put away the originals so they do not get damaged. You can burn your Disk Images to CD or DVD by clicking burn in Disk Utility and then selecting them. You can also restore a hard drive with a Disk Image made from another hard drive by selecting your destination hard drive in Disk Utility, clicking the restore tab on the right-hand pane and dragging the blank destination hard drive to the destination field.

by Ryan, ryan@smalldog.com