OS X Mountain Lion is the second version of OS X that can only be purchased through the Mac App Store. If you haven't yet upgraded to OS X Lion, the new distribution and installation methods may seem a bit foreign. On the plus side, Apple worked out most of the glitches on Lion, so you get the benefit of installing Mountain Lion using a well-understood and reliable method.
If you did upgrade to OS X Lion, you'll find most of the installation process to be very similar. Either way, this step-by-step guide will help ensure that you understand how everything works.
There are several ways to install OS X Mountain Lion. This guide will show you how to perform an upgrade install, which is the default installation and the one that Apple thinks most Mac users will choose. It's not the only option, though. You can also perform a clean install, or install the OS from various types of media, such as a USB flash drive, a DVD, or an external hard drive. We'll cover those options in other guides.
What is an Upgrade Install of OS X Mountain Lion?
The upgrade install process lets you install Mountain Lion over your existing version of OS X, and still retain all of your user data, most of your system preferences, and most of your applications. You may lose some of your apps if they can't run under Mountain Lion. The installer may also change some of your preference files because certain settings are no longer supported or are incompatible with some feature of the new OS.
Before You Perform an Upgrade Install
Most of you won't have any problems with installing and using Mountain Lion, but there's a small chance that your particular combination of apps, data, and preferences will be the one that was never thoroughly tested before Mountain Lion was released. That's one reason why I highly recommend backing up your current system before you start the upgrade process. I prefer to have a current Time Machine backup, as well as a current clone of my startup drive. That way I can revert my Mac to the way it was configured before I started the installation, should I need to, and it won't take long to do it. You may prefer a different backup method, and that's fine; the important thing is having a current backup.
The guides below will show you how to back up your Mac and how to create a clone of your startup drive.
What You Need to Perform an Upgrade Install of OS X Mountain Lion
- A copy of the Mountain Lion installer, which is available from the Mac App Store. You must be running Snow Leopard or later to access the Mac App Store, but you don't have to install Lion before you install Mountain Lion. Mountain Lion will install correctly as long as you're running OS X Snow Leopard or later on your Mac.
- A destination volume for the installation. The Mountain Lion installer can work with internal drives, SSDs (Solid State Drives), or external drives with USB, FireWire, or Thunderbolt interfaces. Basically, any bootable device will work, but because this is a guide to an upgrade install, the target volume must be running Snow Leopard or earlier. If your Mac doesn't meet this requirement, then the Clean Install guide is a better choice for you.
- A minimum of 8 GB of free space; more space is better, of course.
- A minimum of 650 MB of free space for the Recovery HD volume. This is a hidden volume that is created during the installation. The Recovery HD volume contains utilities to repair drives and to re-install the OS if you have problems with a drive.
If you have everything lined up, and you've ensured that you have current backups in place, let's begin the actual upgrade process.