How to Back Up Your Data & Installation Discs

With the advent of the Mac App Store (s aapl), it seems arcane to think that software is still being distributed on disc.  But even if you buy into digital distribution completely, what about all of your existing installation and data discs? What’s a good way to preserve the disc and its contents? Create an image of your disc on your hard drive, that’s how.

Every time you enter a disc into your SuperDrive, it gets mounted to the big directory structure that makes up your computer. We use the term mount because we used to physically mount spools of magnetic tape onto devices that were accessed by computers.  Once mounted, the user can then delve into that particular disc’s file structure and access its content via the Finder.  The same concept holds true for .dmg (or Disk Image) files.

Apple’s Disk Utility has the ability to mount and unmount these devices as well as format, erase and copy file structures.  It’s therefore possible to create a an image or copy of any CD or DVD.  This resulting image file works just like the .dmg files you often download from the Internet and use to install third-party applications, like Firefox and Skype.  In fact, if you open a .dmg file and then type the command ‘mount’ in the terminal, you will see that the operating system is looking at the .dmg file in exactly the same way it looks at discs you load using the SuperDrive.

To preserve the type of file system the optical disc is using, you can Disk Utility’s ability to create images. Here’s how:

  1. Insert a data CD or DVD into your computer’s SuperDrive and launch Disk Utility (located in your [User] > Applications > Utilities folder)
  2. From the source menu on the left, select your disc drive. It should have a CD icon next to the manufacturer’s name and a model number
  3. Click on the New Image icon in the Toolbar at the top of the Disk Utility window
  4. Select a save location as well as a name for the image file you are about to create
  5. Be sure to select “DVD/CD master” as the Image Format and leave Encryption set to none
  6. Click Save

At this point, Disk Utility will create a copy of the CD or DVD that you had in the SuperDrive. To mount this file as a drive, simply double-click on the file in the Finder.  Your file will be mounted just as if the original disc was inserted into your SuperDrive. This only works for data discs, not movies or music.  You can even reverse this process and burn a physical disc from an image that was created by Disk Utility.  To burn a disc from a .cdr image, you need to:

  1. Open the image file in Disk Utility (File > Open Disk Image… in the menu bar)
  2. Find and select the image file
  3. Click on the Burn icon on the Toolbar
  4. Insert a blank disc of appropriate size into the SuperDrive
  5. Click Burn

Disk Utility will burn the disk image from the hard drive to the optical disc.  Again, this only works for data discs, not music CDs or movie DVDs, but it should help you get started on de-cluttering your physical media collection.

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