Macintosh whole disk erase: Using Disk Utility

IMPORTANT NOTE: University drives should only be erased by an IT Professional or other qualified University department such as the IT Support Center.

You will need the startup disc that came with the computer to completely erase the drive. If the startup disc is missing, use Parted Magic.

To completely erase a Macintosh hard drive that runs OS X 10.3.x or above—not just individual files on the drive—you can use the Disk Utility that is built into the Macintosh operating system.

IMPORTANT: Erasing a hard drive deletes all the volumes and files on the drive. Therefore, before you erase the hard drive, if you want to keep any files, copy them to a form of external media (e.g., an external hard drive or a CD).

By default, Disk Utility erases only the information used to access the files, not the data in the files themselves. Therefore, the erased files can be recovered. If you need to erase a disk so that the files cannot be recovered, you can select security options within the utility to do so (i.e., write zeros over the disk space).

You must reboot your computer using the OS X system CD that came with your Macintosh. To do so:

Macintosh OS X 10.3.x or later

  1. Insert the CD into the CD drive.
  2. Hold down the C key during the startup process.
  3. Select your preferred language. You will then see the Welcome to the Mac OS X Installer window.
  4. From the Installer Menu Bar, click Open Disk Utility. You will see the Disk Utility window.
  5. In the left pane of the Disk Utility window, click the drive you want to erase.
  6. In the right pane of the Disk Utility window, click the Erase tab.
  7. From the Volume Format drop-down menu, select Mac OS Extended (Journaled).
  8. In the Name field, highlight the existing text and type the name the hard drive is to have after it is formatted.
    Following are the available security options:
    • Don't Erase Data—This option only rewrites the headers on the disk. Files can be recovered by forensics, disk utilities, and other advanced recovery software.
    • Zero Out Data—There are forensics utilities that, albeit expensive and time consuming, can retrieve zeroed-out data.
    • 7-Pass Erase—This is considered sufficient by government standards to erase data from a disk. It writes random data over the disk seven times. It may take several hours or more to complete this process.
    • 35-Pass Erase—This makes it absolutely impossible to regain any data off the drive. NOTE: This option takes an extremely long time, possibly more than one day.
  9. Click 7-Pass Erase (recommended by UD).
  10. Click OK.
  11. Click Erase.
  12. Confirm that you want to erase. The program will unmount the volume, partition the drive, and rename the volume to the name you typed in step #8 above.