How Apple Boot Camp Works

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Back before 2006 (which is like 100 years ago in the technology industry), there was a clear dividing line between Macintosh computers and PCs. Mac OS couldn't run on PCs, and Microsoft Windows couldn't run on Macs. This created a great rift between users of each system. It wasn't unusual to hear heated arguments between two users about which was the better system. A few brave souls tried to take an all-inclusive approach by trying try to run both using virtualization software, but even that presented limitations. If you wanted to use the full features of both operating systems, you'd have to buy both a Mac and a PC.

But in 2006, that all changed. Because in 2006, Apple began moving away from its PowerPC processors and offered Mac hardware with Intel processors like those used in PCs. This introduced the possibility that Windows and Windows-based applications could run on Mac hardware just as they run on PCs. At the same time, Apple released Mac OS X Tiger (10.4), the first Mac OS to support running on Intel processors [source: Apple, Buchanan].



Boot Camp is software developed by Apple, in cooperation with Microsoft, designed to effectively run Windows on Mac hardware. By using Boot Camp, you don't have to choose whether to install either Mac OS or Windows. Instead, you can install both, and you can switch between them just by rebooting and selecting the other OS.

This article covers how Boot Camp works and how you can set it up on your Mac. Boot Camp has been available as part of Mac OS X since Leopard (10.5), released in 2007. The latest version of Boot Camp as of this writing, Mac OS X Lion (10.7), supports Windows 7 Home Premium, Professional or Ultimate editions [source: Apple].

Before we dive into Boot Camp, let's look at how the partitions work on your Mac's hard drive, and how the Mac knows which partition to use when you boot.

Hard Drive Partitions

Boot Camp software relies on controlling how a Mac boots. To understand how Boot Camp takes control, let's first look at the Mac boot process. Specifically, we need to look at how a Mac reads and uses its hard drive, which stores the operating systems and all your data.

The hard drive is divided into one or more partitions. A partition is a range of physical addresses on the hard drive. In other words, the partition tells the computer where to read and write bits of data inside the hard drive. Information about the partitions on a hard drive is stored in a partition table.



When you boot your Mac, part of the boot process includes accessing the first few bytes of data of the hard drive. Those first bytes point to the partition table. From there, the partition table indicates which partition has the operating system and other data needed to finish booting the Mac.

Normally, when your Mac is fresh out of the box, it recognizes all the available storage space on your hard drive as one single partition. This is sufficient for most users, and it makes it easy to track your total available hard drive space.

However, if you want to install different operating systems on the same hard drive, you have to create different partitions for them. You could use any disk utility to create and format new partitions. Boot Camp, though, takes care of this partitioning for you. Boot Camp will resize your existing Mac OS partition and create and format a new partition for Windows. Boot Camp could also help in partitioning a separate hard drive if you had multiple hard drives in your Mac.

When you boot, how does the Mac know which partition to target? The partition table has an indicator of which partition to use when booting. Your Mac will look for its operating system on that partition. If you have both Mac and Windows, though, you need some way to select between those partitions. Boot Camp's role is to automate that selection so you don't have to worry about partition tables. Using Boot Camp, you'll have two options for switching between your Mac and Windows partitions:

  • Use the Boot Camp utility to indicate you want to switch to the other partition, and then reboot.
  • Use the Option key during the white splash screen while booting, and select the partition you want to use.

Now that you know what Boot Camp's doing, let's look at how to set it up on your Mac.

Preparing to Set Up Boot Camp

The Boot Camp Assistant utility in Mac OS X steps you through the process of setting up Boot Camp.
The Boot Camp Assistant utility in Mac OS X steps you through the process of setting up Boot Camp.
Screencap by Stephanie Crawford for HowStuffWorks

When you set up Boot Camp, you'll be stepping through a wizard known as the Boot Camp Assistant. After set up is complete, you can use the Boot Camp Assistant again to remove or reinstall Windows. To open the Boot Camp Assistant, click on your Finder, select Applications from the left, scroll down and select Utilities, and then double-click Boot Camp Assistant.

Before you continue, make sure you have the following. We'll take a closer look at each of these before going on, including what to do if you don't have one:



  • The install disc or ISO for a supported version of Windows
  • A copy of the Boot Camp Install and Setup Guide
  • A blank CD, DVD, or MS-DOS-formatted storage device such as a USB drive or SD card

If you don't have a Windows install disc, you can download an ISO of Windows and burn that to a disc. You'll need to use this disc in the Mac's CD/DVD drive during your Boot Camp setup. Be sure to use this information when you're selecting which version of Windows to use:

  • Boot Camp for Mac OS X Lion (10.7) supports Windows 7 Home Premium, Professional and Ultimate editions, 32-bit or 64-bit.
  • Boot Camp for Mac OS X Snow Leopard (10.6) supports Windows XP Home or Professional with Service Pack 2, Windows Vista Home Basic, Home Premium, Business or Ultimate, and Windows 7 Home Premium, Professional or Ultimate. Support for 64-bit versions is limited: no 64-bit versions of Windows XP, and 64-bit versions of Vista and 7 only on MacBook Pro models from 2008 or later and iMac and MacBook models from late 2009 and later.

The Boot Camp Installation and Setup Guide is available from the "Introduction" page of the Boot Camp Assistant. There, click "Print Installation & Setup Guide." If you don't want to print it, you can save it as a file by clicking "OK" on the first print dialog, then "Save as PDF" from the PDF menu of the second print dialog.

When you click "Continue" on the "Introduction" screen, you'll have three options available. Assuming you've already obtained the Windows install disc, you can keep the first option unchecked and the last option checked. The middle option is to download the latest Windows support software. This includes all the drivers necessary for Windows to work on your Mac hardware. Keep this option checked, and follow the instructions in the screens that follow to download those and save them to an external storage device (like a USB drive) or blank disc. At the time of this writing, the total download size for the WindowsSupport download saved to an external drive was just under 675 MB.

Now let's take a closer look at the next step in Boot Camp Assistant: partitioning.

Boot Camp Setup: Partitioning

The Boot Camp Assistant gives users a simple slider tool to allocate partition space between Mac OS X and Windows.
The Boot Camp Assistant gives users a simple slider tool to allocate partition space between Mac OS X and Windows.
Screencap by Stephanie Crawford for HowStuffWorks

By default, Boot Camp will reserve 20 GB for your Windows partition and leave the rest for a single Mac OS X partition. You can see this on the partition slider in the Boot Camp Assistant immediately following your download of the Windows support software. If you drag the grey dot between the two partitions on the slider, you can adjust how the hard drive is split between the Mac OS X and Windows.

Before you commit to your slider selection, consider the size of Windows itself and how you'll be using it. Windows 7 requires 16 GB of drive space for the 32-bit version and 20 GB for the 64-bit version. That means the default 20 GB is a tight squeeze for installing Windows 7, and you'll probably want at least 5 to 10 GB more for small software apps and files you'll use exclusively in Windows.



There's a good chance you'll be using Windows to run some specific software. If so, you can add that software's requirements to your total. For example, if you're using Windows to play "World of Warcraft," add at least another 25 GB of space to meet the game's minimum requirements, and you'll probably want more to save game data and install expansions over time.

As you grow your Windows partition, though, don't ignore the space you'll need on the Mac side. The slider should show you the available space you have on the Mac side as you increase or decrease the amount on the Windows side. Boot Camp Assistant will not let you go below 8 GB of available space on the Mac side, but you'll probably want a lot more than that if you use your Mac for storing or editing music and videos.

When you're happy with the slider position, click "Install" to continue. If you haven't installed your Windows disc, Boot Camp Assistant will prompt you to do so. Next, we'll navigate your Windows install and setup.

Boot Camp Setup: Installing Windows

By default, Boot Camp places an icon in your Windows System Tray, which you can use to reboot to Mac OS X.
By default, Boot Camp places an icon in your Windows System Tray, which you can use to reboot to Mac OS X.
Screencap by Stephanie Crawford for HowStuffWorks

When Boot Camp launches your Windows installation, it hands over control to the install disc. The Windows install procedure itself works the same as on a PC. For Boot Camp, there are a couple of things you'll need to select as you step through this procedure:

  • Select the partition named "BOOTCAMP" when asked where to install Windows.
  • Use the drive options to indicate that the BOOTCAMP partition needs to be formatted before installation. By default, the installer will use the NTFS file system.

Finish installing and configuring Windows as you would on a PC. During the reboot step of the install, the Mac should reboot directly back to the Windows partition. Later, we'll look at how to toggle between the Windows and Mac OS X partitions.



With Windows installed, you'll need to install the Windows support software from Apple. Insert the disc or drive you used to save the Windows support download. If the setup doesn't launch automatically, open the drive's file system and launch setup.exe. The installer includes the latest version of the drives that Windows needs to run the Mac hardware, such as the speakers, microphone and webcam.

After you've installed the Apple software, you'll notice a Boot Camp icon in the Windows System Tray. Don't try to remove this, as it provides one of your two options for switching between partitions. Let's see how that works next.

Switching Between Mac OS X and Windows

When you first boot, press "Option" during the Mac's white boot screen to select which partition to boot.
When you first boot, press "Option" during the Mac's white boot screen to select which partition to boot.
Screencap by Stephanie Crawford for HowStuffWorks

Once you've set up Boot Camp, you have three different ways to make the switch between partitions. Let's look at these based on their starting points.

If you're in Windows, you can switch to the Mac OS X partition using the Boot Camp icon in the System Tray. Click the gray diamond-shaped icon, and click "Restart in Mac OS" from the pop-up menu. Then, confirm your choice to reboot to Mac OS X and give the computer about a minute to make the switch.



If you're in Mac OS X, you can switch to the Windows partition using the Startup Disk utility within System Preferences. In the Startup Disk, choose the "Windows on BOOTCAMP" partition, and click "Restart." Then, confirm your choice to reboot to Windows and give the computer about a minute to make the switch.

If the Mac was powered off, you can choose which partition to boot before the Mac selects for you. To do this, press the Option key on the Mac while it's on the blank white boot screen. Within a couple of seconds, the Mac should present the two partitions to you on the screen. Use the arrow keys to select a partition, and press Enter to boot to it. This Option key feature is available either when booting from a powered-off state or if you're rebooting from Windows.

Ready for lots more information about Boot Camp? Switch on over to the next page.

Related Articles

More Great Links


  • Apple. "Apple to Use Intel Microprocessors Beginning in 2006." Apple, Inc. Jun. 6, 2005. (Feb. 13, 2012)
  • Apple. "Boot Camp Installation & Setup Guide." Apple, Inc. 2011. (Feb. 13, 2012)
  • Buchanan, Matt. "Cheetahs, Pumas and Tigers, Oh My: The Two-Minute OS X History Primer." Gizmodo. 2007. (Feb. 13, 2012)
  • Diederen, Jeroen. "Linux on Your Apple Mac | iLinux." (Feb. 13, 2012)
  • Microsoft Corporation. "Windows 7 system requirements." 2012. (Feb. 13, 2012)