This guide walks you through the process of creating a bootable OS X Mountain Lion installer DVD or USB flash drive.
What You Need
You need either a dual-layer DVD and a burner or a USB flash drive. The dual-layer DVD has two layers, which increases the available recording space to about 8.5 GB. The OS X Mountain Lion installer is a bit too large to fit on a standard DVD. Dual-layer DVDs are available anywhere standard DVDs are sold. If your Mac doesn’t have a built-in SuperDrive, use an external DVD burner. Alternatively, use a USB flash drive that can hold at least 5 GB as your bootable media. 8 GB and 16 GB flash drives are also commonly available. Download a copy of OS X Mountain Lion, which you must purchase at the online Apple Store and download it from the Mac App Store. It is stored in the Applications folder on a Mac. The file is called Install OS X Mountain Lion.
Locate the Mountain Lion Install Image
The Mountain Lion install image that you need to create either the bootable DVD or the bootable USB flash drive is contained in the Install OS X Mountain Lion file you downloaded from the Mac App Store. Because the image file is contained in the downloaded file, copy it to the Desktop to make creating the bootable image as easy as possible. Pasting the item to the Desktop takes time. When the process finishes, you have a copy of the InstallESD.dmg file that you need to create bootable copies sitting on the Desktop.
Burn a Bootable DVD of the OS X Mountain Lion Installer
With Mountain Lion’s InstallESD.dmg file copied to the Desktop, you’re ready to burn a bootable DVD of the installer.
Copy OS X Mountain Lion Installer to a Bootable USB Flash Drive
If you can’t burn DVDs, use a bootable USB flash drive. Creating a bootable copy of Mountain Lion on a flash drive isn’t difficult. All you need is the InstallESD.dmg file that you copied to the Desktop and the flash drive. Before you begin, erase and format the USB flash drive. Here’s how: The USB device is erased and partitioned. When that process is complete, the flash drive is ready for you to copy the InstallESD.dmg file to the drive. Here’s how: Disk Utility copies the InstallESD.dmg data to the USB flash device. When the process is complete, you have a bootable copy of the OS X Mountain Lion installer ready for use.
