How you format a Mac hard drive is entirely dependent on what kind of drive you plan on formatting. For instance, is the hard drive internal or external? And if internal, has it been partitioned or are you looking to reformat the entire system to factory state? Whatever your formatting situation, this how-to guide will cover each of these step-by-step.

Before you go messing around in the Disk Utility application, make sure you know what the drive is going to be used for. If it’s an external hard drive, for instance, do you plan on hooking it up solely to Macs or Windows PCs as well? Each one has its own compatible format, so you’ll have to be careful which you choose. FAT 32 is the most compatible disk format which is why it’s the most widely used on USB thumb drives — it’s compatible with both Mac and Windows PCs. HFS+ is the native Mac OS file system, and NTFS is Windows’ (Macs can read what’s on NTFS-formatted drives, but they cannot write).

Before you start formatting any hard drives, make sure you’ve backed up your data! Formatting an external hard drive will delete any information on the device, likewise reformatting your system will essentially bring your Mac back to a clean factory state, thus removing all information you’ve stored on it. Conclusion: Be sure to backup first.