OS X Mountain Lion (10.8) supports several installation options. It may not be evident when you start the Mountain Lion installer, but you can perform a clean install or an upgrade install of the OS.

You can also install Mountain Lion on a range of devices, including your startup drive, an internal partition or volume, or most any external drive you may have.

Another option is to create bootable copies of the installer that can run on a DVD, USB flash drive, or another storage device. This choice lets you keep a version handy in case you need to reinstall the operating system.

Minimum Requirements for OS X Mountain Lion

OS X Mountain Lion has a few special needs that prevent it from running on some older Intel Macs. Even some Macs that can run OS X Lion may not meet the minimum requirement for Mountain Lion.

Here are the devices that can upgrade to Mountain Lion:

  • iMac: Mid-2007-2020MacBook: Late 2008 Aluminum, Early 2009 or newerMacBook Pro: Mid/Late 2007 or newerMacBook Air: Late 2008 or newerMac mini: Early 2009 or newerMac Pro: Early 2008 or newerXserve: Early 2009

Having the right device isn’t enough, however. Your machine also has some minimum requirements it has to meet:

  • A Mac with OS X Snow Leopard (10.6.8) or OS X Lion (10.7)At least 2 GB of RAM8 GB of available space

Preparation: Check the Target Drive for Errors

No matter what method of installation you plan to use with OS X Mountain Lion, first, make sure the target drive is sound, free of errors, and unlikely to fail anytime soon.

Here’s how to do a quick check on your startup drive:

  • Open Disk Utility from the Utilities folder in Applications.
  • Click your drive in the left pane.
  • Click First Aid.
  • Select Run in the window that appears.
  • A message may appear telling you that your drive will lock while Disk Utility checks it. Read the warning and click Continue.
  • First Aid runs and reports any issues it finds.

Back Up Your Mac Before You Upgrade

Individuals who are in a hurry to update to a new OS often forget to back up first. Before you begin the OS X Mountain Lion installation, back up your data and apps. It doesn’t matter what backup method you choose. Some popular options are Time Machine, your favorite third-party backup application, or a clone of your startup drive and all of its data.

Open Disk Utility from the Utilities folder in Applications.

Click your drive in the left pane.

Click First Aid.

Select Run in the window that appears.

A message may appear telling you that your drive will lock while Disk Utility checks it. Read the warning and click Continue.

First Aid runs and reports any issues it finds.

The important thing is to have a current backup in case anything goes wrong during or after the installation. Delaying the installation for a few minutes to perform a backup is better than recreating your data because the power went out during the installation process.

How to Perform a Clean Install of OS X Mountain Lion on a Startup Drive

A clean install of OS X Mountain Lion results in a clean Mac with no old user data or apps—just a fresh start.

Because the target is the startup drive, you have to erase the drive first, which erases the OS X Mountain Lion installer. To avoid this catch-22, create a bootable copy of the installer and then use it to install the OS on the blank drive.

You can also install the OS on a non-startup drive. Unlike this process, which requires you to create bootable media first, there are no special techniques required for a clean install on a non-startup drive.

How to Create a Bootable Installer Copy

This optional step creates a bootable copy of the Mountain Lion installer. With it, you can perform a clean install of Mountain Lion on your Mac’s startup drive, as well as boot from and run Disk Utility and other emergency tools.

You can create a bootable copy of Mountain Lion on any bootable media, including DVDs, USB flash drives, and external volumes.

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