Now use the Erase Free Space option, which also offers 1, 3, and 7 passes of erase, and only empties out unused parts of the disk. After you boot, launch Disk Utility, select the startup volume, and click the Erase tab. First, erase a drive without the overwriting part, and reinstall OS X. There’s a slightly different way to accomplish the same goal. You’ll save a little time if you do an erase without overwriting, then reinstall OS X, then Erase Free Space with an overwriting option. Select Disk Utility from the startup menu, and you can erase your startup drive securely. Restart a Mac and hold down Command-R after the startup chime sounds, and the computer boots into the recovery mode. Then you’d run Disk Utility to erase your startup drive. Securely erase your hard drive with Disk Utility.īefore Lion, you had to boot from a CD or DVD system disk or a third-party utility, like Disk Warrior, or from an external drive with OS X installed. Once is considered enough for regular purposes, while three and seven correspond to different U.S.

When you select a volume in Disk Utility and then the Erase tab, you can click Security Options to pick how many times the drive is overwritten: once, three times, or seven times. That’s been built into Apple’s Disk Utility for years. To get rid of old data in a thorough fashion, you need use a multi-pass approach, in which every bit of storage in the disk is overwritten with new data (often zeroes).

How to clear my startup disk