Tips & Shortcuts

Quick Tip: How to Create a Disk Image


What is a Disk Image? How do you make one? Why would you ever do such a thing? Today's Quick Tip screencast will walk you through to answers to these questions and more. Give us five minutes and we'll teach you everything you need to know.


How to Create a Disk Image

What Are Disk Images?

Disk Images in OS X are a great way to back up, archive, and/or protect any file or folder on your Mac. They are just what they sound like, a virtual disk, or storage device, that you can create and then mount in order to access the files contained inside; just like you mount a physical hard drive by plugging it into a USB, FireWire, or Thunderbolt port on your mac. If you've ever downloaded and installed an Application from the Internet on your Mac, then you have used a Disk Image.

If you've ever downloaded and installed an Application from the Internet on your Mac, then you have used a Disk Image.

You can create Disk Images using Disk Utility. To create a Disk Image you use the New Image button or the Menu Bar to select an option for creating a Disk Image. You can also create a blank Disk Image or create a Disk Image from a folder. Let's look at some specific situations of making a Disk Image.

Create A Disk Image
You Can Create A Disk Image By Clicking The "New Image" Button Or From The Menu Bar
  • Use the Menu Bar to create a new blank Disk Image, a Disk Image from a folder, or from a selected hard drive.
  • Use the New Image button to quickly create a new Disk Image of a selected item.

Creating a Disk Image of a hard drive or CD/DVD

If you want to create a Disk Image of an entire hard drive or partition on a drive, either for backing up or cloning a computer for an office or the like, click and select the hard drive you want to make a Disk Image of and click the New Image button.

In addition to naming the Disk Image and specifying where to save it, you have a few options for security and format:

You Can Set The Security Of Your Disk Image As Well As The Format Type
You Can Set The Security Of Your Disk Image As Well As The Format Type"
  • Choose compressedto create a smaller size Disk Image, but keep in mind it will take longer to open as it needs to uncompressed the data.
  • Read-onlywill make a Disk Image that will open quicker but the size of the Disk Image will be a bit larger. Read/write will allow you to add files to the Disk Image after it's been created if you wish to use the Disk Image for storage, archival, or organization.
  • If you want to password protect the Disk Image you can select an encryption method and inter a password when prompted.

You can also create a Disk Image of a CD or DVD. This is a great way to back up your physical disks. Simply insert a CD or DVD into your ROM drive and select the disk from the list to the left and click New Image.

Select The Hard Drive, Partition, Or CD/DVD You Want To Make An Image Of And Click
Select The Hard Drive, Partition, Or CD/DVD You Want To Make An Image Of And Click "New Image"

Because the Disk Image is being read form the hard drive as opposed to the CD ROM Drive, if it is an installer, the install process will be much quicker. This is good if it is something you have may have to install again or install on multiple computers.

Folders & Blank Disk Images

If you want to create a Disk Image of a specific folder, you can go to File > New > Disk Image From Folder and select the folder for which you want to create a Disk Image. From here the process is the same as above.

You can also create a blank Disk Image. There are many useful reasons for creating blank Disk Images, such as creating a Disk Image that you can use to store and password protect sensitive documents, managing a lot of files or folders that you are moving between computers on a regular basis, or password protecting the contents of a portable USB drive.

When you select Make New Blank Disk Image, you have a few more options than the previous ways. Most notably, you can determine the size of the Disk Image as well as determine if you want it to be a sparse Disk Image, which will automatically expand in size as you add files to it.

New Blank Image
  • Set the size of the new Disk Image You want to create.
  • Selecting a sparse format will add space to the Disk Image as needed, up to the selected size you set.

Once you create your Disk Image, you will see the .dmg file appear and the disk will automatically mount. It will have an icon that looks like a disk drive, much like a physical drive you plug into your Mac. To eject or un-mount the Disk Image, you simply drag it to the trash can or right click and select Eject.


Disk Images are a great way to back up CD or DVD ROMS, or to password protect sensitive files. Using Disk Images can save you a lot of time and trouble should you ever need a backup of a lost disk.

Using them as an organizational tool will also help you stay on top of managing files. I hope this helps you feel more comfortable using Disk Images in your day to day workflow.

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