In fact, there are four ways you can format an external or USB flash drive to achieve varying degrees of compatibility between Macs and PCs. Since Mac OS X and Windows use totally different file systems, the way a drive is formatted can determine what type of computer it will work with. Need to access or transfer files between Mac and PC? As simple as this task sounds, it’s not very straightforward for inexperienced users. Learn a few ways to make your drive Mac and PC friendly. If you have an external hard drive or USB flash drive that you’d like to use on both Macs and Windows PCs, choosing the right file system to format the drive can be confusing.