When you purchase a thumb drive or hard drive and attach or install it in your Mac, you likely will be able to use it right away; however, depending on the uses you intend for the drive, its default setup may not be the most optimal.

In most cases, manufacturers ship drives formatted to the FAT32 filesystem, since this format is universally supported in Windows, OS X, Linux, among other popular operating systems and devices. Even though FAT32 is a convenient format, it is limited in features, including no permissions support, file sizes limited to 4GiB, and the inability to use Apple’s CoreStorage technology for features like encryption.

For Mac OS Only

If you plan on using the drive only with your Mac, then format it to Apple’s most supported format and partition scheme:

1. Attach the drive to your Mac and select it in Disk Utility.
2. Click the Partition tab (this should only appear when the device is selected).
3. Choose the number of desired partitions (volumes) from the drop-down menu. If you do not know, then choose “1 Partition” here to use the entire disk for one storage space.
4. Click the “Options” button and select “GUID” as the partition scheme, then close the options panel.
5. Name each partition on the drive by selecting it and then doing so in the Partition Information section, and choose “Mac OS Extended (Journaled)” as the format to use.
6. Click Apply to make the changes to disk.

When done, you will see the drive umount and then re-mount, and then be available for any Mac system.

Mixed OS Environment

If you plan on using your drive with Windows or Linux PCs in addition to your Mac, then your best bet is to leave the drive formatted to FAT32. If you intend on erasing the drive, then choose “MS-DOS (FAT)” from the format list instead of Mac OS Extended (Journaled) before erasing it. Additionally, while the GUID partition scheme will work in many modern PCs, for compatibility you can choose Master Boot Record as the partition scheme to use. Just be sure to test the drive with a PC or two.

You may notice that Apple supports the relatively new exFAT format, which is an option when you erase a drive in Disk Utility (step 4 above). This format overcomes some of the limitations in FAT32, but is only fully supported by default in the most recent versions of Windows, so unless you are only going to be using the drive with your Mac and with Windows 7 or above, then it may be best to use FAT32 instead of exFAT.

Windows Only

To use the drive only with Boot Camp, a virtual machine on your Mac, or another Windows-only environment, then your best bet is to load the drive in that operating system and format it to NTFS using Windows. While this will make the drive only readable in OS X (at least without modifications to the OS), as is the case with Mac OS Extended in OS X, this will be the most compatible option for use with Windows.