Create A Bootable Mac OSX 10.8 Mountain Lion USB Flash Drive (UFD) – Apple’s next generation operating system (OS) for world’s most number one defined-as Personal Computer will be called as “Mountain Lion”. Any interested users can simply grab it via App Store but just make sure your old Mac still meets OSX 10.8 system requirements.
And if it does, then you are good to go. But just in case if are not so sure about new stuff but still want to taste its greatness without having to sacrifice and throw away your 10.7.x Lion or the Snow Leopard, creating a separate OSX 10.8 installation may be a great option.
By installing it on a separate partitions like in a bootable USB flash drive, you can start a clean OS X 10.8 install even you don’t have Internet connection. But make sure you already have OS X 10.8 Mountain Lion .DMG file extracted. If you have not done so, once downloaded from App Store, go to /Applications/ directory and right-click on “Install Mac OS X Mountain Lion.app” followed by clicking “Show Package Contents” then open the “Contents” directory. Now go to “SharedSupport” then look for a file named “InstallESD.dmg”. Finally simply double-click on InstallESD.dmg to mount it on the desktop.
Alright, assuming you’ve done that part, now it is time to create a bootable SUB flash drive for the OS X 10.8. Thanks to OSXDaily for sharing this trick.
1- Launch Disk utility
2- Connect a USB drive to the Mac
3- Select the USB drive from the left menu
4- Click on “Erase” tab
5- Choose “Mac OS X Extended (Journaled)” as the format
6- Click on the “Erase” button in the corner
7- From the left side, select the formatted USB drive
8- Now click on the “Restore” tab
9- Drag the “Mac OS X Install ESD” image into the “Source” section
10- Drag the formatted partition to the “Destination” section
11- Click on “Restore”
11- You may need to confirm things
12- You may also need to enter your Admin password
13- Now just wait for your Mac to create a bootable OS X Mountain Lion installer drive out of USB drive using the disk image.
That’s it. Once done, do not forget to give it a try by booting to OSX 10.8 via your bootable USB you’ve just created.
Simply reboot your Mac and hold down the Option key to bring up the boot menu. Once it appears, now select the orange “Mac OS X” option and you will boot into the OS X Mountain Lion installer. I am sure from here you are already familiar with the installer as all you need to do is just following the installation procedure. Just make sure you select the right destination drive then install it.