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.