If you have a USB drive, and you plan to use it on both a Mac and PC, things can get a bit tricky here. By default, Macs are with HFS+ (since 2017 there’s new Apple File System, APFS, optimized for flash storage), while PCs are with NTFS. It’s no surprise that PCs and Macs do not work well with each other, due to differences between the two operating systems (Windows vs.