Burning a CD or DVD from an Image File

Mac OS X has "image files" that behave like a virtual CD or DVD. Double-clicking one of these files "mounts" the virtual disc just like inserting a physical disc. Once the disc icon appears on your Desktop, the behavior of a virtual or physical disc is identical.

There are two types of image files:

  • Master Image – a bootable disc with a ".cdr" file name extension.
  • Disk Image – a data disc with a ".dmg" file name extension.

Disk Images are far more common than Master Images.

On occasion, you may need to create a physical disc from a image file.

Four Sample Image Files

This folder has four image files: CD & DVD master images and large & small disk images.

Drag an Image File into Disk Utility

  1. Select the image file you wish to burn in Finder.
  2. Drag the file into the Disk Utility window below the list of drives. A blue line appears when the cursor is in the empty space.
  3. Release the mouse, and the image file name appears at the bottom of the list.

Initiate the Burn

  1. Select the image file name.
  2. Click the Burn button in the toolbar.

Insert a Blank CD or DVD

Choose an appropriate blank disc based on the Disk Image Size:

  • CD-R – up to 650 MB
  • DVD-R – up to 4.7 GB (like this example)
  • DVD+R DL (dual layer) – up to 8.5 GB

Insert the blank disc into your Mac.

Choose the Burn Options

  1. Speed: The choices for burn speed are determined by your Mac's optical drive and the blank disc. Choosing the slowest speed yields the highest quality burn.
  2. Verify burned data: Choosing this option compares the burned disc to the image flle to confirm a perfect burn.
  3. Eject or Mount: After verification, Disk Utility either ejects the disc or mounts it on your Desktop.
  4. Click the Burn button to begin the burn.

Monitor the Burn and Verification

The progress bar makes two passes: Writing track & Verifying.

Verifying is much faster than Writing because the optical drive runs at full speed, reading the newly burned disc.

Label the Disc with a Sharpie

Label the disc as soon as it comes out of your Mac. Use only a brand-name Sharpie pen (any color). Other pens may damage the disc.