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[Mac OS X] Install Mountain Lion on a Separate Partition

[Mac OS X] Install Mountain Lion on a Separate Partition

[Mac OS X] Installing Mountain Lion on a Separate Partition

Of course, you already know that yesterday Apple surprised the whole world with a completely unexpected release of a new version OS X - 10. 8 Mountain Lion, but currently in Developer Preview status, i.e. developers for information. Naturally, this news instantly spread around the world.

Certainly, the desire to see the Mountain Lion (aka Cougar) with their own eyes has also appeared among many ordinary users of Apple computers. But setting the new version, which is in Developer Preview status, as the main system is hardly prudent.

Therefore, I will tell you how to install it in a separate partition of your computer’s disk, which is called "to look at" without updating your current system.

For this we need a new system distribution. The question is where to get it, I think everyone will decide for themselves. 🙂 What I managed to find is a dmg-image, inside of which there is an installer.

So, let's start "taming" the Mountain Lion. 🙂

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Stage 1 - preparatory

First of all, we need to free up disk space for the partition for the new system. To do this, run Disk Utility (Programs - Utilities). On the left side we find and select our hard drive, and on the right side we select the Disk Partition tab, which will display the section of our disk as a rectangle - Macintosh HD (all pictures are clickable) :

In the lower right part of the section, there is a special corner (shown by an arrow), holding which you can resize the section. We need to get something like this:

The minimum amount of free disk space should be chosen based on the following considerations. The system itself will take approximately 6.5 GB, and about the same amount is needed for the installation process. And you will also need a place to install your programs. I recommend choosing a minimum of 15-20 GB. The free space on my hard drive allows me not to be stingy, and therefore, as it is easy to understand from the picture, I freed up about 200 GB. 🙂

Below the freed space, you need to click on the button with the + sign, thereby creating a new section:

Make sure Mac OS Extended (Journaled) is selected as the file system, then click Apply. After a while, a new partition will be created. Close Disk Utility.

Step two - installation

Now, if you, like me, have a distribution in the form of dmg-image, we need to mount (double click) this image and drag the installer from it to any directory, for example, to Programs or to Desktop. Then run it:

Click continue. On the next screen, the installer prompts us to install a new system on top of the current one. We don’t need this at all, so we click on the button Show all drives:

Select our second partition and press the button Install:

The first stage of the installation will begin, at the end of which you will be prompted to restart the computer to continue the installation:

Press the Reload button. The installation will continue after a reboot. There is no need to describe the further installation process - it is quite simple. Just carefully read what the system installer says.


After installing a new system, the default boot will be given to it. That is, every time you restart or turn on the computer, Mountain Lion will be loaded. You probably don't need this, so you can make your main system bootable by default by going to Boot Volume in System Preferences. There you need to select the partition with your main system and click the Restart button:

In the future, to boot a new system, you can choose the partition with the new system as the boot volume in the same way and boot it.

Or, easier, hold down the Alt key while restarting or turning on the computer, which will allow you to select the desired system:

Good luck!

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