How to Delete the Hard Drive on a Mac

If you want to install a new version of Mac OS X or want to sell your Mac, you may need to delete the data on your Mac's hard drive. You can use your Mac's installation DVD and Disk Utility to erase all data on your main hard drive, as well as any external hard drives you may have. Disk Utility also offers several secure erase options so that the data cannot be recovered in the future.

...
You can erase your Mac's hard drive for both security and a fresh install.

Step

Insert the Mac OS X installation disk into your computer and reboot. Hold the "C" key when the computer plays the start-up sound to boot from the disk.

Step

Choose "Open Disk Utilities" from the "Installer" menu above the "Installer" screen. Do not click "Continue" on the Installer screen.

Step

Choose the hard disk that you wish to erase from the list on the right and select the "Erase" tab. Click "Security Options" if you wish to securely erase the drive by writing in zeros and click "OK."

Step

Click "Erase" to delete all information on the hard disk.