In a Windows-dominated world, computer peripherals usually aren't designed to work with Macs right out of the box. Buy a new flash drive, plug it in, and the results are unpredictable. It may work well enough, not at all, or even exhibit unreliable functionality. The fix is to format a USB drive on Mac before you start using it. This not only clears off any data that might be stored on the drive, but also makes sure it's set up with a file system that your Mac is designed to use.
Why It's Necessary to Format USB Drives for Macs
Mac and Windows computers use different file systems, only some of which are cross-compatible. In computing, it's easy to think of a file system as the system that a computer uses to store, identify, and retrieve files. Without a file system, a computer wouldn't be able to store new files, and stored files would be impossible to retrieve.
When you buy a new USB flash drive, SD card, hard drive, or any storage media, there's a good chance that it either isn't formatted or that it was formatted at the factory for use with Windows computers. Some of these devices will still work with your Mac out of the box, but you're better off formatting the drive yourself to use a Mac-specific file system like Mac OS Extended (Journaled) or a format that works across platforms like ExFat.
Before you format your USB drive, make sure to back up any files that you have already stored on the drive. Formatting will completely erase the drive. You may also want to use Time Machine to back up your computer just in case you make a mistake and format the wrong drive.
How to Format a Flash Drive on Mac
To format a USB flash drive to work with your Mac, follow these instructions:
Connect a USB drive to your Mac.Koson Rattanaphan / EyeEm
It should show up on your Desktop (in this case, it's the icon called BACKUP).
Open Disk Utility.
You can access Disk Utility by searching with Spotlight, or navigating to Applications > Utilities > Disk Utility.
Select the drive you want to format, and click Erase (located at the top center of the window.)
Make absolutely sure that you select the correct drive during this step. The drive you select will be formatted, so if you choose the wrong drive you may lose important data.
Select the Mac OS Extended (Journaled) format. This format is designed specifically for Macs and works with both current and older models.
If you need to transfer large files between your Mac and a Windows computer, select the exFAT format. For transferring smaller files between operating systems, use MS-DOS (FAT) or FAT32.
Wait for the process to finish, then click Done.
How to Format a USB Drive on Mac With Multiple Partitions
When you format a USB drive that has multiple partitions, you will find that only one partition is formatted. The other partitions will remain exactly as they were before, including their original file system and whatever files are stored there.
If you want to format your USB drive such that it has a single partition that's formatted for use with your Mac, follow these instructions:
Connect a partitioned USB drive to your Mac.
Open Disk Utility.
Select the partition you want to remove, and click Partition.
Click the - symbol located under the pie chart.
Select the newly partitioned drive, and click Erase.