Deleting a Hard Drive? Why Reformatting is Critical

Your computer has hit the end of its life with you and like a long-term relationship you decide to part ways. In both cases you want to make sure that the next person won’t have access your most private information. That is way reformatting your hard drive is a much better option than going through it and selectively removing files, especially if that computer moves on to someone else. There are a variety of reasons why reformatting a hard drive is part of a repair path or used when reinstalling Mac OS X 10. Whatever your reason, here are some steps to take and explanations of what each option means.

Deleting your hard drive

Before you start you need to understand that there are two types of formatting level: low and high. Both levels will erase and reformat your hard drive but differ in how comprehensive they are. A low level format takes the total usable space and divides it into sectors and tracks. This creates the foundation that a high level format needs to build a logical formatting structure. Typically any new hard drive you purchase comes preformatted as low-level and you will only need to perform a high-level. When it comes to erasing personal data the low level is the most comprehensive in that it returns all the binaries back to "0".

Low level format

The options you have available to you with a low-level format depend on which version of Mac OS X Disk Utility you have on the Installer disk. Prior to 10.3.x, all installers included Zero All Data as an erase option. This performs a one-pass zeroing of all binary sectors and is fairly comprehensive when it comes to cleaning your hard drive of any personal data. After Mac OS X, version 10.4 included additional secure erase options including Zero All Data once, seven times, and 35 times multiple pass and direction rewrite options. The multi-pass and direction rewrite zeros all data in a scrambled and non-linear fashion and is the most comprehensive to date.

High level format

A high level format, on the other hand, creates a logical formatting structure of the hard disk. This comprises data structures that include the catalog tree, volume information blocks, volume bitmap, boot blocks, the extents tree and the data tree. These structures are collectively called the directory structure and play a large role in maintaining information about the disk, its location and the data stored on it.

Commonly you will see HFS (Hierarchical File System) come up in reformatting using this process. It’s represented by your disk icon on your desktop. Essentially this process is used as the next step in preparing the hard drive to accept an operating system and user information by providing a directory structure. Used alone it does not zero any data on the hard drive; rather it overwrites it and ignores previous bad blocks.

When considering options for "cleaning" your hard drive and preparing a Mac for someone else to use, low-level formatting is the better option. Deleting files and/or performing a high-level reformatting will not provide you with all the protection you might hope for. A low-level formatting is typically more time consuming but eliminates any privacy concerns you might have when your computer starts seeing other people.

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