
Drag the formatted partition to the “Destination” section, then click on “Restore”.Drag the previously mounted “Mac OS X Install ESD” image into the “Source” section.Now select the formatted USB drive from the left side and click on the “Restore” tab.Select the USB drive from the left menu and click on “Erase” tab, choose “Mac OS X Extended (Journaled)” as the format, then click on the “Erase” button in the corner.Launch Disk utility and connect a USB drive to the Mac.Make the OS X Mountain Lion Install Drive Double-click on InstallESD.dmg to mount it on the desktop.Open the “Contents” directory and then open “SharedSupport”, looking for a file named “InstallESD.dmg”.Go to the /Applications/ directory and right-click on “Install Mac OS X Mountain Lion.app” selecting “Show Package Contents”.Download OS X 10.8 Mountain Lion from the App Store.Download OS X Mountain Lion and Extract the DMG File

If you already have the Mac OS X Mountain Lion install DMG extracted, skip this first set of steps and jump directly to making the bootable drive below. We’ll walk through the process here, but don’t forget to check OS X 10.8 system requirements for the destination Mac before beginning. By creating a bootable install drive, you can perform clean OS X 10.8 installs, install it on separate partitions, and install OS X Mountain Lion on Macs that don’t have internet connections.
