How to Create an OS X Mountain Lion 10.8 Installer USB Drive

In this tutorial you will learn how to create a bootable OS X Mountain Lion 10.8 Installer USB drive. This way you will be able to install to install  OS X Mountain Lion 10.8 on the MacBook Air, for example, without using an external USB SuperDrive.

1. Download a copy of OS X Mountain Lion 10.8

You can download OS X Mountain Lion from the Mac App Store.

2. Extract the contents of the OS X Installer App

After the Mac App Store has finished the download you can find the OS X Mountain Lion installer app in your Applications folder.

You can now right click (ctrl + click) the OS X Mountain Lion installer app and select Show Package Contents. Open the Contentsfolder then the SharedSupport folder. This is where you will find the InstallESD.dmg file.
Copy this file to your Desktop. Make sure you use Copy and Paste, simply dragging the file to your desktop might only create an alias.

Double clicking the file you have just copied to your desktop will mount the disk image and open a finder window showing its contents.

You can close this window and open the Disk Utility. Just hit command + space and start typing "disk utility". Now you can also connect your USB drive to your Mac.

3. Restoring the Installer to a USB Drive

Select the USB drive and click the Erase tab. Choose Mac OS X Extended (Journaled) as Format and click the Erase button.

Now select the USB drive you have just formatted and click in the Restore tab.
Note that under Source the drive itself is selected.

Click on Mac OS X Install ESD and drag it to the Source field.
Now click on the USB drive you have formatted before and drag it to the Destination field.
Your Disk Utility window should now look something like this:

Click Restore and confirm will loose all it's data and enter the admin password when requested.

The Disk Utility will now create a bootable OS X Mountain Lion 10.8 USB drive.
This process can take between 20 and 50 minutes depending on your computers performance.

When finished, backup your data (this type of installation will erase all the data on your Macs hard drive), reboot your mac and hold down the option ket.
You can now select the bootable USB drive (shown as an orange drive) and begin the OS X installation.

Do you have any questions or suggestions? Please leave a comment.