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How do I create a Macintosh disk image?

A popular way to distribute your creations online is via disk images. Using a disk image allows you to create a compressed, virtual disk that other Mac users can open on their desktop. The following instructions will help you create your first disk image:

  1. Start by launching “Disk Utility” that’s located in the Utilities folder of your Applications folder. This application lets you create and edit disk images. #Create a new blank image by selecting Images > New > Blank Image… from the Disk Utility menu bar.
  2. In the dialog box that appears, Enter “Test Image” in the Save As box, then set the Size to 5 MB or whatever size is appropriate for the files you want to distribute. Leave the Encryption set to “none” and Format as “read/write disk image”.
  3. After pressing “Create” you’ll see a series of progress windows and then a new file named “Test Image.dmg” will be created on your desktop. You’ll also see a new disk icon labelled “Test Image”.
  4. At this point, you can add any files you’d like to the “Test Image” disk. You can also customize the Finder view using Command-J. Check out our help on how to add a background image or a custom disk icon.
  5. After you are done modifying the “Test Image” disk, eject it with Command-E.

At this point, you’ll see that the the “Test Image.dmg” file uses 5 MB of disk space, even if you are only using a small portion of the allocated space. This leads us to the next set of steps which will compress the disk image:

  1. In the “Disk Utility” application, select Images > Convert… from the menu bar.
  2. Enter “Download.dmg” into the Save As box—this will be the file you upload to your web server. Then, navigate to the disk image you have already created and edited: Desktop > Test Image.dmg. Finally, set the Image Format to “compressed” and leave the Encryption as “none”.
  3. After a series of progress dialogs, you’ll see “Download.dmg” appear on your desktop. You can open this disk image by double-clicking. After you have verified that everything looks OK, go ahead and upload the file to your webserver.

If you have problems downloading the disk image from your website, you may need to configure some server settings.

You can also edit the original disk image, “Test Image.dmg” by double-clicking on the file name. After you eject the disk image, you can do another Convert to compress and prepare a new file for download.

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