Deleting a hard drive, also referred to as erasing a drive, is a way to wipe a drive clean. This process puts the drive back into its original state with zero files, folders, or programs on the drive. It is recommended that you erase the contents of a hard drive before getting rid of a computer or before disposing of a hard drive being replaced. Another use for this process is to “start fresh” and do a clean install of the Mac OS X operating system along with any programs and files you want to reinstall.
Insert the Mac OS X CD that came with your computer into the computer’s CD drive.
Click the “Apple” logo in the upper left of the screen and select “Restart.” Click “Restart” again if prompted.
Press and hold down the “C” key on the keyboard during the start up process. You must press and hold “C” before the gray loading screen appears. A “setup” menu will appear.
Choose your language from the list and locate the “Installer Menu bar.” Select “Open Disk Utility” from the list of options. The “Disk Utility” window appears.
Look in the left side of the “Disk Utility” window for the name of the “drive” you want to delete. For example if you have a hard drive with multiple partitions choose the drive letter associated with the partition you want to delete. Or if you want to delete the entire hard drive select the drive at the top of the list usually labeled as “C:/,” “Mac,” or a custom name you gave the drive when first using the Mac.
Choose the “Erase” tab from the right side of the “Disk Utility” screen. Under the “Volume Format” heading choose “Mac OS Extended (Journaled)” from the drop down menu.
Type in the “name” that you want to give the drive once it is blank in the “Name” text field. You can leave this blank as well.
Select either “7-Pass Erase” or “35-Pass Erase” from the list of “Erase” options. Choosing either of these will delete any and all files and data on the drives. The “7-Pass Erase” is sufficient to randomly write over and delete all data and may take a few hours. The “35-Pass Erase” may take upwards of a day to complete.
Click on “OK” followed by “Erase.” When prompted confirm that you want to erase all contents on the drive.
Consider backing up important files and folders before beginning the erase procedure.
Deleting or erasing a hard drive will remove all files and data on the drive. You will not be able to retrieve any data once the process is complete.
University of Delaware: Erasing Mac OS X hard drives [http://www.udel.edu/pnpi/tools/erase/mac/erasedisk.html]