Step 3: Select the startup disk in Disk Utility.Step 1: Boot your Mac into macOS Recovery mode.The position of buttons and background color may slightly differ in different operating systems, but the overall process remains the same. Make sure you have a backup to crucial files. FAQ about how to format startup disk on MacĮrasing the Mac startup disk will cause all data stored on it permanently wiped out. Why won't my Mac let me erase the hard drive? Step 3: Select the startup disk in Disk Utility

Step 1: Boot your Mac into macOS Recovery mode This post explains how to format the Mac startup disk with step-by-step guides. You can upgrade to Mountain Lion or Mavericks from App Store after that.Sometimes, you fail to reinstall macOS or want a clean reinstallation, then you will need to format the startup disk. If your Mac came with Lion, the Install OS X option will download and install the latest minor version of Lion. Quit Disk Utility and choose Install OS X.Open Disk Utility, select the Macintosh HD volume, open the erase tab, and press the erase button.If others search for how to do a normal erase and reinstall, erase the main OS X partition (like Macintosh HD) instead of the whole drive: If you have one of those Macs, you erase the whole drive from the recovery partition, and it is not in fact possible to reinstall OS X without starting up in Internet Recovery mode after that, you can probably use Recovery Disk Assistant instead. Some older Macs support a recovery partition but not Internet Recovery mode. But if you restart the Mac, it will start up in Internet Recovery mode, which means that it downloads a disk image of the recovery system from Apple's servers, and you can then install OS X on the empty drive. When I did this with my MacBook Air, I restarted it after I had erased the drive, so I don't know if it is possible to reinstall OS X from the recovery partition without relying on Internet Recovery mode. It also erases the hidden recovery and EFI partitions. Open Disk Utility, select the drive (not the Macintosh HD volume), open the erase tab, set the format to Mac OS Extended (Journaled), and press the erase button.Start up from the recovery partition by holding command-R.You can erase the drive and reinstall OS X using the recovery system:

Reformat mac hard drive