Formatting a hard drive or USB flash disk to be compatible with both a Mac and Windows PC is extremely easy, we’ll walk you through the process in a few simple steps. Remember, formatting a drive erases all data contained on it so back up important files before proceeding.
Launch Disk Utility, found within /Applications/Utilities/
Connect the drive you wish to format for dual compatibility to the Mac
Click the drive name on the left side list in Disk Utility, and then click the “Erase” tab
Click the “Erase” button to format the drive for Mac & Windows PC compatibility
Drives format very quickly, though the total time taken will depend on the size of the drive.
The resulting file system is compatible with all versions of Mac OS X, Windows 95, 98, Windows XP, Vista, 7, even Windows 8, it’s one of the most widely recognized and usable file system formats. This makes FAT an ideal file system to use for USB flash drives or external hard drives that are intended for use in environments with multiple operating systems. The primary downside to using FAT32 is the file size limit, which limits files on the drive to being 4GB in size or less. If you require single files to be larger than 4GB, use exFAT instead, though you will lose some compatibility with older versions of OS X and Windows.
If you only intend on using the drive on a Mac it’s recommended to format for Mac OS X use only using the journaled file system. Just be aware that the Mac-only formats are typically not readable by Windows machines.