Clients and friends often ask me what to do with an old computer and how to make sure data on their old machine doesn’t fall into the wrong hands when donating or recycling. Below are instructions for how to permanently erase ALL personal data stored on the hard drive.
Important: When a drive is “erased”, the data is NOT actually removed. Many “erase” or “format” procedures only delete the drive’s *directory* – the place on the drive which tells the computer where the actual files are stored. Unless you specifically tell the erase utility to write new data (usually zeros) to the entire disk surface, data may remain on the drive and could be recoverable by the technically inclined.
Disclaimer: Be careful here – you’re about to ERASE data, PERMANENTLY. Make triple sure you’re selecting the right drive to erase and when in doubt STOP. If necessary, make a backup of the data to another drive before proceeding. Data WILL BE PERMANENTLY erased using the steps below. Proceed at your own risk…
Method 1: Boot from the Recovery Partition and Erase
1: Turn on your Mac and immediately press and hold Command (⌘)-R. Release the keys when you see an Apple logo, spinning globe, or other startup screen.
2: Choose “Disk Utility” from the Utilities window and press “Continue”:
3: When Disk Utility launches, choose “Show All Devices” from the pop-up menu on the upper left:
4: Select “Macintosh HD” (unless you renamed the hard drive – in that case, select the name of your internal drive) from the list of devices in the left column.
5: Click the “Erase” icon in the upper center of the Disk Utility window, then click the “Security Options…” button on the lower left: