How to Format a Hard Drive on a Mac

Macintosh computers, made by Apple, use a different file system than modern PCs.

The Disk Utility on a Mac computer allows you to format and partition a hard drive, including external drives or flash drives. Formatting a hard drive clears data from the drive so it is no longer visible to the computer. By partitioning, you can divide a hard drive into sections. Each partition acts as if it were a different drive and can be mounted and unmounted independently in the Finder. If you want to permanently delete files to prevent others from recovering them, it's important to use the advanced security format options to write over the data on the disk.

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Instructions

1. Formatting a Hard Drive

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     Launch Disk Utility on your Mac. The program is located in the Utilities folder within Applications in the Finder. To quickly launch Disk Utility, just click the magnifying glass icon in the upper-right corner of the desktop. Type "Disk Utility" in the Spotlight search field that appears and press "Enter."
     
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     Select the hard drive you want to format in the left menu of the Disk Utility. Note that physical disks are all left-aligned. Disk partitions appear beneath the disk entry and are indented to the right. An easy way to verify that you have selected an actual disk and not a partition is that the Partition tab only appears in the main window when you have selected a disk.
     
   • Select the "Erase" tab at the top of the main window. Click the "Format" menu to see the available format options. Select "Mac OS Extended (Journaled)" if you will be using the disk with Mac computers. If you plan to use the drive on a Windows-based PC, select "MS-DOS (FAT)." Windows PCs are unable to read Mac Extended partitions. Most flash drives use the FAT (file allocation table) system because it is universally accepted on most operating systems; however, it does not work well with large hard drives or very large files.
     
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     Click the "Security Options" button if you want to permanently erase the data on the hard drive. The default setting will not securely erase the data. It only disables access to the files, leaving them easily recoverable by any data-restoration software.
     
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     Select "Zero Out Data" to erase the data on the hard drive. The utility will write zeros over the data, making it difficult to recover. Select "7-Pass Erase" to write over the data seven times with zeros. This method meets the US Department of Defense 5520-22 M standard. Select "35-Pass Erase" to write over the data 35 times. Of course, these last two methods will take seven and 35 times longer, respectively, to finish.
     
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     Click the "Erase" button. A dialog box opens to confirm you are about to erase the disk. Read the details and click "Erase." The amount of time it takes will depend on which security option you selected. When formatting is completed the amount of room available on the disk will be displayed in the bottom-right of the main window. The drive will appear in the left menu with a single partition using the name you typed.
     

   Partitioning a Hard Drive

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     Launch the Disk Utility if it is not already open, then select the hard drive in the left menu. Click the "Partition" tab in the main window. The Disk Utility shows you a representative picture of the hard drive, which is divided into sections if there is already a partition on the drive.
     
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     Click the "+" button beneath the picture of the hard drive. By default, the Mac OS Extended (Journaled) format is already selected. Use this format unless you plan to share the disk with a Windows-based PC, in which case you can select "MS-DOS (FAT)" from the Format menu. Type a name for the partition in the "Name" text field. Type a size for the partition in the "Size" text field. Click "Apply."
     
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     Delete a partition by clicking its picture, then clicking the "-" button at the bottom. You will lose all of the information in the partition when you click "Apply."
     

Tips & Warnings

• If you plan to use install Microsoft Windows on your Mac's internal hard drive, use Boot Camp. Boot Camp will guide you through the process of partitioning the hard drive and formatting the partition to prepare it for Windows.
• Take care before using a format option other than Mac OS Extended (Journaled). Mac OS Extended by itself does not allow the operating system to track changes in files, leading to potential problems if you need to recover them. Mac OS Extended (Case-sensitive) allows the operating system to distinguish between files based on case-sensitive letters, but this feature can cause problems with software that doesn't support case-sensitivity. ExFAT is a Microsoft format similar to FAT, but it is not as universally accepted as FAT.
• Always back up your data before attempting to format or partition a hard drive.