In the left column, select the drive you want to format. (In this example, I will format the 1.04GB Generic Flash Disk.) If you have a partitioned drive and you want to format one of the partitions but not the whole drive, select a partition.
Click on the Format pull-down menu. A list of six formats will appear. You need to select one—but which one?
Mac OS Extended is the format specifically for the Mac, and it comes in two key variations, Mac OS Extended and Mac OS Extended (Journaled). Mac OS Extended (Journaled) maintains a journal of disk changes, which is helpful in case the drive suddenly loses power or is otherwise unexpectedly unavailable. If you are formatting a drive that will be dedicated to a Mac, we recommend using Mac OS Extended (Journaled). Time Machine requires a drive or partition on a drive formatted with Mac OS Extended (Journaled).
There are two other Mac OS Extended formats available that offer case-sensitivity. With these two formats, files with the same names but different case treatments (e.g., diary.doc or Diary.doc) are considered two separate files and can both reside on your drive.
If you are formatting a drive that you want to use on both a Mac and Windows (such as a portable hard drive or flash thumb drive), consider using MS-DOS (FAT) or ExFAT. MS-DOS (FAT) has some limitations (such as a 4GB file size limit), while ExFat requires that a Mac be running OS 10.6.5 or later.
Select a format and give your drive a name.
Step 3: Security Options
Click on the Security Options button. Here, you determine how to erase the data that’s currently on the drive. Apple provides brief explanations of each method.
Select one of the methods further down the list, and you'll need more time to format the drive—in some cases, it can take many, many hours. For example, with the Don’t Erase Data option, formatting the 1GB flash drive in this example is almost instantaneous. Formatting using the 35-Pass Erase option takes two hours.
Select a Secure Erase Option that you’re comfortable with and click OK.
Step 4: Erase
This next step will actually format your drive. Review your settings and make sure they are what you want.
Click on the Erase button on the lower part of the Disk Utility interface. A confirmation dialog will appear. When you’re sure you want to proceed, click on Erase. Then sit back and wait, or call Mom, or grab a refreshing beverage. You can see the progress of the format at the lower right.
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