Erasing a mac hard drive is actually a very simple task. In the most recent versions of Mac OS X, Apple has included a Utility to perform this and many other tasks related to various disks. This program is conveniently named Disk Utility, and can be accessed from the Utilities folder inside the main Applications folder.
Upon opening Disk Utility, you will see a list of all disk drives connected to your computer. These include, but are not limited to: your built-in hard drive (and any partitions you have created), external drives, USB sticks, CDs, or DVDs.
Selecting any one of these disks will allow you to perform numerous operations on them. To erase the contents of a disk entirely, click over to the “Erase” tab. Here, you have yet more options, as you can reformat the disk entirely, such as if you want to change an NTFS disk to an OS X Journaled format. You can also erase the “free space” on a given disk, so as to purge any leftover data from previous erasures/deletions. These options are, of course, in addition to the basic erasure method that will get rid of any data on a given disk. Note that you obviously can’t erase the drive or partition from which you are running the disk utility.
There are a few things that one must consider before erasing a drive in this manner.
1. Do I have a backup?
Backups are crucial in today’s world. You’ll never know when you’ll need to re-access some data, and it’s better to be safe than sorry. Backup systems are very inexpensive in this day and age, and can cost less than $100.
2. Do I no longer need the data?
Assuming you have a backup, there is little point in purging an entire drive if you will only restore it in a week. Erasing and rewriting large chunks of data can be quite time-consuming, so think before you click.
3. Do I know what I’m doing?
This is the most critical of all precautions. Far too few users know that reformatting a drive will cause all the data on said drive to be lost. Understand the consequences of deleting your data and be aware of exactly what is getting deleted.
With all of this in mind, any disk maintenance you have to do should be both easy and worry free, thanks to the built-in Disk Utility.