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Media Disposal (Mac) - Securely Erasing a Hard Drive in Mac OS

When disposing of an old computer, you should be mindful of any personal data you may have left behind on the computer. Files containing sensitive information (e.g. tax documents, student grades, etc.) could be accessed by unauthorized people if the hard drive of the computer isn't securely erased. This document explains how to securely erase a hard drive on a Mac OS.
IMPORTANT: These directions will result in the loss of all data on the hard drive on which Secure Erase is run. Extreme care should be taken to ensure that you have backed up your data and followed the precautions outlined within this document. Once this process is done, your data will be lost forever. The DoIT Help Desk is not liable if you accidentally erase important content using the method described in this document.

If you understand the risks, click here to show/hide the directions.

Preparing to wipe your hard drive

There are a few things you should do before you securely erase your hard drive.

  1. Make sure that you have backed up any important files from the computer you are going to erase
  2. Safely disconnect any USB hard drives or flash drives from the computer you are going to erase to reduce the risk of accidentally erasing those drives

Erasing your hard drive

Once you have prepared your computer by backing up important files and disconnecting any external hard drives or flash drives, you can erase your hard drive using Disk Utility:

  1. Insert your Mac OS Install CD/DVD into your drive
  2. Restart the computer and hold down the C key on your keyboard as soon as the gray loading screen appears. This will boot the computer from CD/DVD.
  3. Select your preferred language. You will then see the Welcome to Mac OS Installer screen.
  4. From the Utilities menu in the top menu bar, select Disk Utility
  5. Disk Utility will open, as shown below. Click on the hard drive that you want to erase in the left menu. For example, we have selected 'Macintosh HD' which is the default name. The drive you are erasing may be different, so take care on this step.


  6. Click on the Erase tab, as shown below.


  7. Click on the Security Options button.


  8. Select 7-pass Erase and click OK


  9. Click the Erase button to begin the secure erasure.


  10. Once this process has begun, you will likely need to wait a few hours for it to complete.

Once this is complete, you can power the computer off and dispose of it as appropriate.

Newer Mac Versions

For more information on the erase process for mac versions Ventura and Monterey, please visit this link

For more information all other newer versions, please visit


Keywordsmedia disposal hard drive harddrive hdd disk drive formatting securely erasing wiping erased wiped disk utility mac os x osx   Doc ID20057
OwnerHelp Desk KB TeamGroupDoIT Help Desk
Created2011-08-29 14:50:29Updated2023-09-27 12:40:52
SitesDoIT Help Desk
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