OS X Mountain Lion supports several different 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 wide range of devices, including your startup drive, an internal partition or volume, or just about any external drive you may have, including USB flash drives.
If you feel up to a bit of fiddling around, you can also create bootable copies of the installer that can run on a DVD, USB flash drive, or any bootable external drive you may have lying around, looking for a purpose in life.
In this article, we've put together a list of all of the OS X Mountain Lion installation options.
OS X Mountain Lion has a few special needs that unfortunately will 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.
This list of the minimum requirements for running Mountain Lion includes the usual data, such as the amount of RAM and disk space you'll need. It also includes a list of Macs that are specifically supported by the Mountain Lion OS.
Make sure your Mac meets the minimum requirements for running OS X Mountain Lion before you get your heart set on installing it.
No matter what method of installation you plan to use with OS X Mountain Lion, one of the first orders of business is to make sure that the target drive is sound, free of errors, and unlikely to fail anytime soon.
This step is often overlooked, and can lead to unpleasant results during or after an installation. So, before you go any further, make sure that the target drive is in tip-top shape.
In the hurry to update to a new OS, this is another crucial step that individuals often forget. Before you begin the OS X Mountain Lion installation, back up your data and apps. It doesn't matter what backup method you choose; Time Machine, your favorite third-party backup application, or a clone of your startup drive and all of its data.
The important thing is to have a current backup in case anything goes wrong during or right after the installation. Delaying the installation for a few minutes to perform a backup is better than frantically trying to recreate your data because the power went out during the installation process.
Although it's not required for the upgrade install of OS X Mountain Lion, a bootable copy of the Mountain Lion installer is a handy thing to have around. 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 drives.
By default, the OS X Mountain Lion installer will perform an upgrade install. The installer will upgrade your current OS (you must be running Snow Leopard or later) to Mountain Lion, while leaving all of your user data in place. The installer will also leave most, if not all, of your applications, system preference settings, and application settings in place.
The upgrade install is the most common method of installing a new OS. The advantage is that it doesn't wipe out your existing data, so you can get back to work (or play) faster than if you perform a clean install.
The Mountain Lion installer is capable of performing a clean install on any startup or non-startup drive. Unlike a clean install on a startup drive, which requires you to create bootable media first, there are no special techniques required for a clean install on a non-startup drive.
The clean install process on a non-startup drive assumes that your target drive doesn't contain an OS. For this guide, we'll also assume that you've recently completely erased the target drive, so that this is truly a clean install.
The advantage of a clean install is that you're not carrying over any old data that may be corrupt or incompatible with OS X Mountain Lion; that in fact, you're starting clean. That means your user data and apps aren't being copied as part of the installation routine. Once the install is complete, you will have a drive that is in almost the same condition as the day you purchased your Mac, except that it now has OS X Mountain Lion installed as the OS.
A clean install of OS X Mountain Lion on your Mac's startup drive is conceptually the same as installing it on a non-startup drive. You have all the same considerations; you will have a clean Mac with no old user data or apps; just a fresh start to work from.
The main difference is the additional steps required to perform the clean install on the startup drive. Because the target is the startup drive, we have to first erase the drive, which of course will erase the OS X Mountain Lion installer. To avoid this catch-22, we'll first create a bootable copy of the installer and then use it to erase the drive and install the OS.