Apple logo black background Mac screenshot 001

Most people are content with booting their Mac straight into OS X, but certain multi-boot situations warrant choosing a different startup disk. But why would anyone in their right mind have multiple operating systems on their computer, you ask.

Well, if you like trying out new things out before they’re available to everyone, chances are you keep the latest beta of OS X installed on a separate partition.

Besides, some people like yours truly prefer to keep a bootable USB thumb drive in a safe place for times when something terribly wrong goes with their Mac.

There are two ways to choosing a startup disk.

One involves choosing a boot disk via a System Preferences pane called Startup Disk, which my colleague Jeff recently covered. This tutorial deals with the other method which involves picking a boot disk as your Mac is starting up.

This tutorial will educate you on choosing a boot disk during the startup process using a feature of OS X called Startup Manager and explain why and when to use Startup Manager over selecting a startup disk in System Preferences.

Let’s get started.

What’s a startup disk?

A startup disk is a partition of a drive or a volume that contains a usable operating system. Your startup disk doesn’t have to contain OS X.

For example, your Mac can boot directly into Windows if you’re using Boot Camp 6. It can also boot into Ubuntu or any other operating system supported by your Mac’s hardware.

As mentioned before, you can, one, set your computer to automatically use a startup disk using System Preferences, and two, temporarily override this choice at boot time using Startup Manager.

What is Startup Manager?

Startup Manager is a built-in application that you can invoke during the startup process to pick a volume to boot your Mac from.

How to choose a startup disk at boot time

To pick a disk to start your Mac from while it’s booting, follow these simple steps for using OS X’S built-in feature called Startup Manager, which can be invoked via a simple keystroke.

Step 1: Turn on your Mac by pressing the power button, or restart it if it’s already on by choosing Restart in the Apple menu.

Step 2: Press and hold the Option (⌥) key immediately upon hearing the startup chime and release the key after Startup Manager appears. Startup Manager will scan connected drives and will present drive icons of any volumes it finds, as shown below.

OS X Startup Manager Mac screenshot 001

Step 3: Highlight the volume you want to use by using your mouse or trackpad, or left and right arrow keys.

Step 4: Double-click or press the Return key to boot your Mac from the volume you just selected. Keep in mind that your Mac can only start up from a disk containing an operating system.

Tip: You can also attach external hard drives with an operating system: Startup Manager will automatically add bootable volumes as you connect them.

How to change your default startup disk

To tell your Mac to automatically use a specific startup volume each time your restart or turn it on, open the System Preferences application in the Dock and click the Startup Disk pane. You will be presented with various disk icons, as shown in Jeff’s video walkthrough embedded below.

Now select the system you would like to use to startup your computer and click the Restart button. From this point on, your Mac will always boot into the selected startup disk until you change your choice in System Preferences or temporarily override it through Startup Manager.

Startup Manager vs. System Preferences > Startup Disk

As explained before, choices you make via the Startup Disk pane will stick until you choose another one in System Preferences or temporarily override these defaults at boot time in Startup Manager.

OS X Yosemite System Preferences Startup Disk Mac screenshot 001

Full tutorial: how to choose a startup disk using System Preferences.

So when should you use Startup Manager over System Preferences?

Basically, if you want your Mac to boot automatically into Windows 10 every time it’s restarted or turned on, use System Preferences > Startup Disk. Want to boot into Windows, Ubuntu or whatever but just this one time, without changing your default startup disk?

Use Startup Manager instead.

Startup Manager won’t let you select a startup disk?

If you cannot choose your startup disk in Startup Manager, make sure that it contains a bootable copy of an operating system such as OS X, Windows or Linux.

Simply formatting a drive or partitioning a disk won’t cut it because Startup Manager looks for partitions and connected drive that contain a usable operating system.

If you’re interested in creating a dual-boot environment on your Mac, check out these easy to follow tutorial that cover deploying Yosemite and El Capitan on a separate partition and USB flash drive:

For additional insights, browse our archive of how-to posts, tips and tutorials.

Five common use cases for Startup Manager

There are many situations that warrant using Startup Manager. Here are some of the more obvious scenarios that average users might encounter:

1. Install an operating system from external media

If you’re old-school and your Mac has an optical drive connected to it, you can insert a disc containing an installer for OS X, Linux, Windows or other supported operating system and boot directly into the installer via Startup Manager. A usable operating system can also reside on a FireWire, Thunderbolt or USB external drive. As long as the disk is bootable, it should show up in Startup Manager.

2. Temporarily override default startup disk

As mentioned before, you should use Startup Manager to choose a startup disk for a single session as it won’t permanently change your default startup disk selected in System Preferences. Let’s say Yosemite is your default startup disk and you have El Capitan on another partition. You can use Startup Manager at boot time to temporarily override Yosemite and start up your computer straight into El Capitan.

3. Boot into other OS natively

Sometimes you may be wondering what’s life like on the “other side.”

In addition to running another operating system alongside OS X using virtualization software such as Parallels Desktop, it’s also possible to boot your Mac directly into a “foreign” operating system via Startup Manager. Typically, I would boot my Mac into Microsoft’s Windows 7 whenever I feel like playing that first-person Windows shooter that everyone’s talking about.

4. Software development and testing

People who develop software for a living typically have multiple instances of OS X to test their apps in multiple environments in order to ensure they run without a hiccup. In addition, many bloggers, journalists and power typically keep OS X betas separate from stable OS X releases. Startup Manager makes it ridiculously easy to choose between them at boot time.

5. Troubleshoot startup issues

Has your Mac been acting up lately?

An improper shutdown, forced restart or power interruption can lead to file system errors that may prevent your computer from starting up. Choosing a different boot device is typically the first step in resolving common startup issues. And to be 100 percent on the safe side, I have another copy of OS X installed on a USB drive should something go terribly wrong with my Mac and I’m in the middle of doing my work.

Other ways to start up your Mac

Your Mac can start up in a number of different ways, including the following methods that our tutorials provide step-by-step instructions for:

  • Safe ModeSafe Mode disables certain features of OS X and loads only essential components to make troubleshooting software issues simpler. In addition, Safe Mode includes an automatic disk check and repair which might resolve boot problems and allow you to start up your computer successfully.
  • Verbose ModeVerbose Mode is a text-only environment which displays status messages as the startup process progresses. Use Verbose Mode to resolve issues with kernel extensions and custom hardware. If that doesn’t sound too sexy, you can enter Verbose Mode to see what’s going on behind the scenes and watch as OS X is loading its components.

We will be covering more ways to start up your Mac in future tutorials.

See also:

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  • Ryan

    Quick question- can I make it so whenever I turn on my computer, startup manager comes up WITHOUT me pushing ‘option’ and then I can select which OS?

    • pdrake007

      +1 for this feature. The amount of times I’ve switched it on and forgot to press ‘option’ and then had to wait for it to boot in and then restart again grrr.

    • Mathew Ike

      HELP I NEED This question ryan asked too , severely bad. can someone help me please ! i want to know the answer to this question. my “option” key on my keyboard broke so the only way for me to do this now is with the question ryan asked.