Apple Posts Directions For Zeroing Data On Hard Drives In Mac OS X

Apple has added a new article to the Knowledge Base explaining how to zero the data on a hard drive. Appleis Knowledge Base (sometimes referred to as the KBase) is a central location for all of Appleis support documents and other important information.

If youive ever sold a computer or a hard drive, youive made sure to erase all of your personal information first, right? Right? If you donit, you probably should. The best way to ensure no data can be recovered is to "zero the data" on the drive. Zeroing a drive overwrites everything on the drive with zeroes, making data recovery very difficult, though never impossible to the right people with the right tools. Many people have asked how to do this with Mac OS X, and this new KBase article explains how.

In order to zero a disk, you will need OS X 10.2.3 or later. From Apple:

Mac OS X: How to Zero All Data on a Disk

This document explains how to zero all data on a disk, a practice that makes data on an erased (initialized) disk less recoverable [emphasis TMOis].

Warning: This document discusses procedures for erasing a disk entirely. Be sure to make backup copies of any files you wish to keep before performing any procedures discussed in this document.

About zeroing data

The information on your hard disk is written in just zeros and ones, known as binary. A special type of file on the disk, called a directory, indicates which groupings of binary digits constitute files. If you erase a disk by doing a quick initialization, the diskis directory is emptied. This is analogous to removing the table of contents from a book but leaving all the other pages intact. Since the system can no longer identify the files in the absence of this table of contents, it ignores them, overwriting them on an ongoing basis as if they were not there. This means that any file on that disk remains in a potentially recoverable state until you fill the disk with new data. You may notice that the Finder references "available" space, not "empty" space. This can help to remind you that a disk is only truly empty when you deliberately make it that way.

The "Zero all data" option is one way to do that. Zeroing data takes the erasure process to the next level by converting all binary in the empty portion of the disk to zeros, a state that might be described as digitally blank. This significantly decreases the chance that anyone who obtains your hard drive after it has been initialized will be able to recover your files. It is good to do this at least once before selling or otherwise disposing of a computer or hard drive. For greater security, zero all data two or more times. For high security applications, consider having the hard drive destroyed by a professional hard drive disposal service.

Zeroing all data takes longer than a normal disk initialization, up to several hours for a large hard drive, so you should plan accordingly.

Availability of zero all data feature

  • For Mac OS X, zeroing is available in version 10.2.3 or later.
  • The zero all data option should work with any hard drive originally shipped from Apple as part of a Mac OS X-compatible computer.
  • Zero all data only works for whole disks. If you have partitioned, you cannot zero an individual partition.
  • This option may or may not work with third-party hard drives.

You can read the entire Knowledge Base article, including detailed instructions on how to do it, at Appleis Web site.