To create an image backup of an external disk drive using the OS X Disk Utility found in the Applications/Utilities folder, take the following steps after attaching the drive to the Apple computer.
- Open Disk Utility, from the Applications/Utilities directory.
- Click on the external disk drive in the left pane of the utility to select it.
- Click on File, then select New and Disk Image from, e.g. Disk Image from "TOSHIBA EXT" for an external Toshiba USB drive.
- You will then be prompted to give the image a name and can select the directory where you wish it to be stored. You can also select whether the image will be compressed and whether it will be encrypted.
- Click on Save to initiate the creation of the disk image. When prompted that "diskimages-helper wants to make changes. Type your password to allow this.", provide a password for an account with administrator privileges on the system. When the image has been created, you will see it listed in the left pane of the Disk Utility window.
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