Performing a clean install of OS X Mountain Lion erases all the data on the target disk. It contains a bootable system with utilities for performing basic disk repair, as well as the ability to reinstall the OS if necessary. This is a hidden partition created by the Mountain Lion installer.
650MB of free space for the Recovery HD partition.A minimum volume size of at least 60GB provides sufficient room for the OS, user data, apps, and some free space. Upon reviving the computer with Command+R+Power, the system took me all the way back to OS X Lion. After a successful reset, the battery died and the power went off but after powering the computer back on, I got the question mark folder on the screen against a black background. You can squeeze Mountain Lion onto a smaller drive, but there won't be much space left for user data and applications. I was using OS Mojave before resetting my hard disk. The target volume must be at least 8GB in size.
The following qualify: iMac, Mid-2007 or newer, MacBook, Late 2008 Aluminum, or Early 2009 or newer, MacBook Pro, Mid/Late 2007 or newer, MacBook Air, Late 2008 or newer, Mac mini, Early 2009 or newer, Mac Pro, Early 2008 or newer, Xserve, Early 2009. You also need a Mac running OS X Snow Leopard (10.6) or later to access the Mac App Store. Before you install Yosemite be sure to check you have the right Mac. The OS X Mountain Lion minimum requirements guide lists the Macs that can run Mountain Lion, as well as recommendations beyond the minimum.
Navigate to Contents > Shared Support, and you should see a disk image called "InstallESD.dmg." We will restore this disk image to our flash drive (or other disk) using Disk Utlity.Screen shot courtesy of Coyote Moon, Inc. Start by right-clicking (or control-clicking) on the "Install OS X Mountain Lion" app, which should be in your main "Applications" folder after downloading. If you like doing things yourself, however, the process is still pretty straightforward for any user comfortable with right-clicking and drag-and-drop. The process will take about 30 minutes or so using USB 2.0 (it should be faster if you have a USB 3.0-compatible flash drive and newer Mac).
You'll basically need to click four buttons: "10.8 Mountain Lion," "Use this copy," "Create a boot disk," and, if you're using a USB flash drive as recommended, "An 8 GB USB thumb drive." It's really that simple Lion Diskmaker takes care of the rest. Once you install a working copy of any version of 10.6 on that hard drive and boot up the MacBook with it, you can download the combo update for 10.6.8, which gives you access to the Apple Store, where you can buy, download and install Mac OS X 10.7 Lion. Just download the Lion Diskmaker app, unzip it, and run it.
(Why not rename the app to something more generic like "OS X Diskmaker"? Gète says he just likes the existing name better, and besides, it's less likely to catch the ire of Apple's lawyers.) His app automates the process of making a bootable install disk for both Lion and Mountain Lion-just run the app and let it do its thing. If you find digging in to bundles and using Disk Utility to be tedious or bothersome, you can thank developer Guillaume Gète for making Lion Diskmaker. You can also burn the installer to a DVD-R, but booting and running the installer from an optical disc is s-l-o-w. Other external drives will also work, but make sure the type works with all your Macs-USB is the most universal. We recommend a USB flash drive for your backup installer they're cheap and easy to store and transport.