Use Boot Camp Assistant to Partition Your Mac's Drive

 Boot Camp Assistant, part of Apple's Boot Camp, serves two functions in getting a Mac ready to run Windows. Its main purpose is to help you partition your hard drive, to create the necessary Windows partition. If you decide to delete Windows at some point in the future, Boot Camp Assistant can restore your Mac to its pre-Windows configuration.

In this guide, we'll look at using an early version of Boot Camp Assistant to partition a Mac hard drive.

If you're using Boot Camp Assistant 4.x or later, you should use the guide: Using Boot Camp Assistant 4.x to Install Windows on Your Mac.

You will need:

  • An Intel-based Mac
  • OS X 10.5 or later
  • Available hard drive space (I recommend at least 20 GB)
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First Things First: Back Up Your Data

Time Machine
Courtesy of Apple

Fair warning: You're about to partition your Mac's hard drive. The process of partitioning a hard drive with Boot Camp Assistant is designed not to cause any data loss, but when computers are involved, all bets are off. The partitioning process alters the way data is stored on your drive. If something should unexpectedly go wrong during the process (such as your dog tripping over the power cord and unplugging your Mac), you could lose data. In all seriousness, plan for the worst, and back up your data before doing anything else.

I mean it. Back up your data. I'll wait. If you haven't already, try using Time Machine to back up your data. Time Machine is included with Mac OS X 10.5 and later, and it's very easy to use. You can also use the third-party backup software of your choice. The important thing is to back up your data on a regular basis, including now; how you do it is up to you.

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Getting Ready to Partition Your Drive

Using Boot Camp Assistant to Partition Your Mac’s Hard Drive
Boot Camp Assistant can not only create a Windows partition, but remove an existing one as well.

Boot Camp Assistant is automatically installed as part of OS X 10.5 or later. If you have the beta version of Boot Camp Assistant, which was available for downloading from Apple's web site, you'll find that it no longer works, because the beta period has expired. You must be using OS X 10.5 or later in order for Boot Camp Assistant to function.

Launch Boot Camp Assistant

  1. Launch Boot Camp Assistant by double-clicking the 'Boot Camp Assistant' application located at /Applications/Utilities/.
  2. Print a copy of the Installation & Setup Guide by clicking the ‘Print Installation & Setup Guide' button.
  3. Click the 'Continue' button.
  4. Select the ‘Create or remove a Windows partition’ option.
  5. Click the 'Continue' button.
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Select a Hard Drive to Partition

Using Boot Camp Assistant to Partition Your Mac’s Hard Drive
Pick the drive you want to hold the Windows partition.

After you select the option to create or remove a Windows partition, Boot Camp Assistant will display a list of the hard drives installed in your computer. For many individuals, this will be a short list, limited to the drive that came with the Mac. Whether you have one hard drive or several, select a drive to partition.

Select a Hard Drive to Partition for Windows

  1. Click the icon for the hard drive that will be the new home for Windows.
  2. Select the ‘Create a second partition for Windows’ option.
  3. Click the 'Continue' button.
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Determine the Size of Your Windows Partition

Using Boot Camp Assistant to Partition Your Mac’s Hard Drive
Use the slider to divide the existing hard drive into two partitions, one for the existing OS X and one for Windows.

The hard drive you selected in the previous step will display in Boot Camp Assistant, with one section labeled Mac OS X and the other labeled Windows. Use your mouse to click and drag the nub between the sections, to expand or shrink each partition, but don't click any of the buttons yet.

As you drag the nub, you'll notice that you can only shrink the Mac OS X partition by the amount of free space that is available on the selected drive. You'll also notice that you can't make the Windows partition smaller than 5 GB, although as I mentioned earlier, I don't recommend making it smaller than 20 GB.

You may also notice that there are two predefined sizes to choose from, via the two buttons located just below the display of the partitions. You can click the 'Divide Equally' button, which, as you might have guessed, will split your drive in half, using half of the available space for Mac OS X and half of the available space for Windows. This of course assumes that there's enough available free space on the drive to split things equitably. Alternatively, you can click the '32 GB' button, which is a good general-purpose choice for a Windows partition, again assuming you have enough free hard drive space to create a partition this size.

Set Your Partition Sizes

  1. Adjust your partition sizes
  • Use the nub to select a custom size
  • Use the buttons to select the pre-defined sizes
  • Click the ‘Partition’ button when ready.

Partitioning a drive usually takes some time, so be patient.

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Your New Partitions Are Ready

Using Boot Camp Assistant to Partition Your Mac’s Hard Drive
Once the partitioning is completed, you can either quit or start the Windows installation process.

When Boot Camp Assistant finishes partitioning your hard drive, the Mac partition will have the same name as the original unpartitioned hard drive; the Windows partition will be called BOOTCAMP.

At this point, you can quit Boot Camp Assistant or click the 'Start Installation' button, and follow the onscreen instructions to install Windows on the BOOTCAMP partition.