how to format a iMac

Install or Reinstall Lion/Mountain Lion from Scratch

Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Erase the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.
2. After ** loads select your startup volume (usually Macintosh HD) from the left side list. Click on the Erase tab in the ** main window.
3. Set the format type to Mac OS Extended (Journaled.) Click on the Erase button and wait until the process has completed.
4. Quit ** and return to the main menu.

Reinstall Lion: Select Reinstall Lion/Mountain Lion and click on the Install button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

hi i have a imac and this wont work it just keeps booting up in to the loggin screen any help would be great?

this isnt working for me

I am trying to erase my hard drive as I plan to sell my iMac. I have selected my hard drive, set the security settings to the highest level. But when I click erase it says that is unable to unmount the disk. What can I do?