As Redmond Pie noted, since there's no physical installation source for the Mountain Lion, some users may face difficulties if anything goes wrong with their Mac while installing the update; they may not even get access to the downloaded installer on their devices. Having an independent bootable USB drive or SD Card also makes sense in case you want to install Mountain Lion on multiple computers without having to download it time and again.
The Lion DiskMaker application has been updated to allow users to make a bootable USB or SD Card installer for the Mountain Lion.
The application is programmed with AppleScript and can be used now with Mac OS X 10.6, 10.7 and OS X 10.8 to burn a DVD or build a bootable drive from Mac OS X Lion or OS X Mountain Lion Installation program.
Users need to have a SuperDrive and a writable DVD (single layer, 4,7 GB for Lion, or dual-Layer, 8,5 DVD-R) to burn the DVD and to build a bootable disk, a USB thumb key drive, a USB or Firewire drive or an SD-Card with minimum of 8 GB storage.
Given below are the steps, showing how to make a Mountain Lion bootable USB/SD Card/DVD drive using the Lion DiskMaker.
Must note that Lion DiskMaker will erase the volume or the drive you chose. Don't forget to backup your data first.
Step 1: Download Mountain Lion from the Mac App Store.
Step 2: Download the latest version of Lion DiskMaker (current version is 2.0rc2).
Step 3: Open the compressed file and run the executable file.
Step 4: Now, the program window will give you three buttons containing user options. Select the bullton showing "Mountain Lion (10.8)". It should find the Mountain Lion image.
If the utility doesn't find the image, go to the Applications folder and find the copy of Mountain Lion you downloaded. Now follow these steps:
- Right click on the downloaded file and select "Show Package Contents".
- Go to "Contents" and jump inside the "SharedSupport" folder and you'll find a file titled "InstallESD.dmg".
Step 5: Lion DiskMaker will now give you two options - "Burn a DVD", or "Create a boot disk". Select "Create a boot disk".
Step 6: Ensure that your 8GB or greater USB Stick/Drive/SD card is mounted. Choose partition and proceed.
For more information, click here.