Chapter 19

When Good Mac Laptops Go Bad


Bullet Understanding why you can be a tech

Bullet Putting basic troubleshooting precepts to work

Bullet Using Mark’s Troubleshooting Tree

Bullet Getting help for your MacBook

Bullet Running Windows — yes, Windows — on your MacBook

I wish you weren’t reading this chapter.

Because you are, I can only surmise that you’re having trouble with your MacBook, and that it needs fixing. (The other possibility — that you just like reading about solving computer problems — is more attractive but somewhat more problematic.)

Consider this chapter to be a crash course in the logical puzzle that is computer troubleshooting: the art of finding out What Needs Fixing. I tell you what to do when you just plain can’t solve the problem yourself.

And then? I expose the BKS (Best Kept Secret) about your MacBook — the feature that many MacBook owners have never heard of and would never imagine. I demonstrate how you can run Windows alongside macOS Big Sur, both cohabitating on your Mac laptop! (Mac purists need read no further when they get to this section.)

One final word: You’re going to encounter a lot of Tips and Mark’s Maxims in this chapter. I learned all of them the hard way, so I recommend committing them to memory.

Repeat after Me: Yes, I Am a Tech!

Anyone can troubleshoot. Believe it, and put these common troubleshooting myths to rest:

  • It takes a college degree in computer science to troubleshoot. Tell that to my troubleshooting daughter. She’ll think it’s a hoot because she owns a MacBook, as well as uses Apple computers in the classroom, and she fixes minor problems all the time. (She doesn’t consider herself a Mac “guru,” either.) You can follow all the steps in this chapter without any special training.
  • I’m to blame. Ever heard of viruses? Failing hardware? Buggy software? Any of those things can cause the problem. It’s Mark’s Maxim time:

    Marksmaxim Don’t beat yourself up! Your laptop can be fixed.™

  • I need to buy expensive utility software. Nope. You can certainly invest in a commercial testing and repair utility if you like. My favorite is Drive Genius 6 from Prosoft Engineering (, but a third-party utility isn’t a requirement for troubleshooting. (I do, however, consider an antivirus application to be a must-have, and you should have one already. Hint, hint.)
  • There’s no hope if I can’t fix it. Sure, parts fail and computers crash, but your Apple Service Center can repair just about any problem. And (ahem) if you backed up your laptop (as I preach throughout this book), you’ll keep that important data, even if a new internal drive or motherboard is in your future.
  • It takes forever. Wait until you read the number-one rule in the next section: The first step takes but 10 seconds and often solves the problem. Naturally, not all problems can be fixed so quickly. But if you follow the procedures in this chapter, you should fix your MacBook (or at least know that the problem requires outside help) in an afternoon.

With those myths banished, you can get down to business and start feeling better soon.

Step-by-Step Laptop Troubleshooting

In the following sections, I walk you through my should-be-patented Troubleshooting Tree, as well as the Big Sur built-in troubleshooting application, Disk Utility. I also introduce you to a few keystrokes that can make your MacBook jump through hoops.

The number-one rule: Reboot!

The simple fact is that rebooting your MacBook can often solve problems. If you’re encountering these types of strange behavior with your laptop, a reboot might be all you need:

  • Intermittent problems with communicating over a network
  • A garbled screen, strange colors, or screwed-up fonts
  • The swirling Beach Ball of Doom that won’t go away after several minutes
  • An application that locks up
  • An external device that seems to disappear or can’t be opened

To put it succinctly, here’s a modest Mark’s Maxim:

Marksmaxim Always try a reboot before beginning to worry. Always.

If you’re in the middle of a program, try to save all your open documents before you reboot. That might be impossible, but try to save what you can.

As your first (and best) option for shutting down, click the Apple menu (App) and choose Shut Down. If you need to force a locked application (one that’s not responding) to quit so that you can reboot, follow these steps to quash that locked application:

  1. Click the App menu, and choose Force Quit.

    The Force Quit Applications dialog appears (see Figure 19-1). Note that you can also press Option+⌘   +Esc to display the dialog.

  2. Click the offending application and then click the Force Quit button.

When you get everything to quit, you should be able to click the App menu and choose Shut Down (not Restart) without a problem.

Snapshot of forcing a recalcitrant application to take off.

FIGURE 19-1: Force a recalcitrant application to take off.

If your MacBook simply won’t shut down (or you can’t get the offending application to quit), do what must be done:

  1. Press and hold your laptop’s power button until it shuts itself off.

    You have to wait about 5 seconds for your MacBook to turn itself off. If you’re using a MacBook Pro or MacBook Air with a Touch ID sensor, press and hold the Touch ID sensor for a count of 5 to 6 seconds instead.

  2. Wait about 10 seconds.
  3. Press the power button/Touch ID sensor again to restart the computer.

After everything is back up, check whether the problem is still apparent. If you use your laptop for an hour or two and the problem doesn’t reoccur, you’ve likely fixed it!

Special keys that can come in handy

Some keys have special powers over your MacBook. I’m not kidding! These keys affect how your road warrior starts up, and they can really come in handy while troubleshooting.

Safe Mode

You can use Safe Mode to force Big Sur to run a directory check of your boot drive and disable any login items that might be interfering with your system. Follow these steps:

  1. Choose  ⇒    Shut Down to turn off your laptop.
  2. Press the power button to restart the computer.
  3. Immediately after you hear the start-up tone, press and hold down the Shift key, and keep holding it down until you see the boot progress indicator.

    After Big Sur boots, you’re in Safe Mode.

  4. Use Disk Utility (or a commercial utility application) to check the operation of your MacBook.
  5. When you’re ready to return to normal operation, restart your MacBook, this time without pressing the Shift key.

Start-up keys

Table 19-1 provides the lowdown on start-up keys. Hold down the indicated key either when you push the power button or immediately after the screen goes blank during a restart. (As I just mentioned, the Shift-key shortcut to Safe Mode is the exception; you should press Shift and hold it down after you hear the start-up tone.)

Some of the keys and combinations in Table 19-1 may never be necessary for your machine, but an Apple technician might instruct you to use them.

All hail Disk Utility, the troubleshooter’s friend

Big Sur’s Disk Utility is a handy tool for troubleshooting and repairing your MacBook’s drive. You can find it in the Utilities folder in Launchpad.

TABLE 19-1 Start-Up Keys and Their Tricks


Effect on Your MacBook


Displays a system boot menu, allowing you to choose any bootable operating system on your laptop


Boots in Safe Mode


Starts your MacBook in Target Disk mode (using your Thunderbolt or USB-C port)

⌘   +V

Shows macOS Console messages (also called Verbose Mode)

⌘   +R

Boots from the Big Sur Recovery HD volume

⌘   +Option+P+R

Resets Parameter RAM (PRAM)

Fire up Disk Utility to open the rather-powerful-looking window shown in Figure 19-2.

Snapshot of the physician of drives: the Big Sur Disk Utility.

FIGURE 19-2: The physician of drives: the Big Sur Disk Utility.

In the left column of the Disk Utility window, you can see

  • The physical drives in your system (the actual hardware).
  • The containers (the formatted portions of the drives on your system).
  • The volumes (the data stored on the drives, which appears as a drive icon on your Desktop).

    Technical Stuff You can always tell a volume because it’s indented below the Container entry. (If you don’t see physical drives and containers as well as volumes, press ⌘   +2 to show all devices.)

  • Any CD or DVD loaded on your MacBook.
  • USB or Thunderbolt external drives.

    Figure 19-2 earlier in this section shows that I have one internal drive (the Apple SSD entry) and one USB flash drive (the PNY USB 2.0 entry). The internal drive has one volume (Colossus), and the external USB flash drive has one volume (Guardian).

Technical Stuff The information at the bottom of the Disk Utility window are the specifications for the selected drive or volume. This info includes capacity and available space for a volume, or connection type and total capacity for a drive.

Disk repair made easy

Disk Utility can check the format and health of both drives and volumes, and you can correct any problems it finds by clicking the First Aid button.

Technical Stuff Using Disk Utility to repair your drive carries a couple of caveats:

  • You may not be able to repair problems on your boot drive or boot volume immediately. This limitation makes sense because you’re using that drive and volume right now.

    If First Aid finds a problem on your boot drive but reports that it can’t fix that error, boot your MacBook from the macOS Recovery HD volume. Reboot and then hold down the ⌘   +R keyboard shortcut immediately after you hear the start-up chord. Then run Disk Utility from the window that appears. Because you’ve booted your laptop from the Recovery HD volume, you can repair those problems with your start-up drive. (You should be able to select your boot hard drive or volume and click the First Aid button.)

  • You can’t repair CDs and DVDs. CDs and DVDs are read-only media and, thus, can’t be repaired (at least by Disk Utility).

    If your MacBook is having trouble reading a CD or DVD with an external drive, wipe the disc with a soft cloth to remove dust, oil, and fingerprints. Should that trick fail, invest in a disc-cleaning contrivance of some sort.

To check and repair problems by using First Aid, follow these steps:

  1. Choose Go  ⇒    Utilities to open a Finder window with the contents of the Utilities folder; then double-click the Disk Utility icon.
  2. In the list on the left side of the Disk Utility window, click the drive or volume you want to check.
  3. Click the First Aid button; then click the Run button that appears.
  4. Click Done to exit First Aid.

    If you made changes or had to boot from the macOS Recovery HD volume, Disk Utility may prompt you to reboot after repairs have been made.

Figure 19-3 illustrates the details you’ll see if you click Show Details to expand the display. Although some of the messages might include cryptic Linux details, you can still tell from the figure that the operation is successful (and you get that snazzy green check mark). All is well!

Snapshot of First Aid reporting that this drive is error-free.

FIGURE 19-3: First Aid reports that this drive is error-free.

Using Mark’s MacBook Troubleshooting Tree

As hip-hop artists say, “All right, kick it.” And that’s just what my MacBook Troubleshooting Tree is here for. If rebooting your laptop didn’t solve the problem, follow these steps in order until you either find the solution or run out of steps. (More on that topic in the next section).

Tip If you’re not sure quite what’s producing the error, this process is designed to be linear — followed in order. But if you already know that you’re having a problem with one specific peripheral or one specific application, feel free to jump to the steps that concern only hardware or software.

Step 1: Investigate recent changes

The first step is a simple one that many novice MacBook owners forget. Simply retrace your steps and consider what changes you made to your system recently. Here are the most common culprits:

  • Did you just finish installing a new application? Try uninstalling it by removing the application directory and any support files it may have added to your system. (And keep your applications current by downloading the most recent patches and updates from the developer’s website.)
  • Did you just apply an update or patch to an application? Uninstall the application, and reinstall it without applying the patch. If your MacBook suddenly works again, check the developer’s website or contact the application’s technical support department to report the problem.
  • Did you just update Big Sur? Updating macOS can introduce problems into your applications that depend on specific routines and system files. Contact the developer of the application, and look for updated patches that bring your software in line with the latest Big Sur updates.
  • Did you just make a change in System Preferences? Return the options you changed to their original settings; then consult Chapter 5 for information on what might have gone wrong. (If the setting in question isn’t listed in Chapter 5, consider searching the macOS online Help system or the Apple support website for more clues.)
  • Did you just connect (or reconnect) an external device? Try unplugging the device and then rebooting to see whether the problem disappears. Remember that some peripherals need certain application software to run; without those applications installed, they don’t work correctly. Check the device’s manual or visit the company’s website to search for software you might need.

If you didn’t make any significant changes to your system before you encountered the problem, proceed to the next step.

Step 2: Run Disk Utility

The next step is to run Disk Utility and use First Aid. The earlier section “Disk repair made easy” shows how to complete this task on your Big Sur boot drive.

Step 3: Check your cables

Cables can work themselves loose, and sometimes, they fail. Check all the cables to your external devices — make sure that they’re snug — and verify that everything’s plugged in and turned on. (Oh, and don’t forget to check for crimps in your cables or even Fluffy’s tooth marks.)

Tip If a Thunderbolt or USB device acts up, swap cables around to find whether you have a bad one. A faulty cable can have you pulling your hair out in no time.

Step 4: Check your Internet and network connections

Now that always-on DSL and cable-modem connections to the Internet are the norm, don’t forget an obvious problem: Your laptop can’t reach the Internet if your service provider is down or your network is no longer working!

When you’re at home, a quick visual check of your DSL or cable modem usually indicates whether a connection problem exists between your modem and your ISP. My modem, for example, has a set of informative activity lights that I always glance at first. But if your laptop is connected to the Internet through a larger home or office network, and you can’t check the modem visually, you can check your Internet connection by pinging

  1. Click the Spotlight icon at the right end of the Finder menu bar, and type Network Utility in the search box.
  2. Click the Network Utility entry.
  3. Click the Ping tab.
  4. Enter in the Address box.
  5. Click Ping.

    You should see successful ping messages. If you don’t get a successful ping and you can still reach other computers on your network, your cable modem, DSL modem, or service provider is likely experiencing problems. If you can’t reach your network at all, the problem lies in your network hardware or configuration. (In an office environment, your network system administrator will be happy to help you at this point, especially if you’re his or her blood relative.)

Step 5: Check your Trash

Check the contents of the Trash to see whether you recently deleted files or folders by accident. Click the Trash icon on the Dock to display the contents. If you deleted something by mistake, right-click the item in the Trash and choose Put Back from the shortcut menu.

I know this one from personal experience: A slight miscalculation while selecting files to delete made an application freeze every time I launched it.

Step 6: Think virus

If you’ve made it to this point, it’s time to run a full virus scan. Make sure that your antivirus application has the latest updated data files. My antivirus application of choice is the excellent ClamXAV ( I can also recommend Sophos Home Free from Sophos Ltd (

Tip If a virus is detected, and your antivirus application can’t remove it, try quarantining it instead. Quarantining disables the virus-ridden application and prevents it from infecting other files. (Check the documentation or the Help system for your antivirus application to learn how to quarantine files.)

Step 7: Check your login items

Big Sur might encounter problems with applications you’ve marked as login items in System Preferences. Your account’s login items are applications that run automatically every time you log in to your MacBook. If one of these login items is to blame for your laptop’s problems, your MacBook will encounter some type of trouble every time you log in. (This is usually the case when you receive an application error message each time you start the computer.)

To check the boot process, it’s time to use that fancy Safe Mode that I discussed earlier in the chapter. Restart your MacBook, and press and hold down the Shift key after you hear the start-up tone. Login items are disabled when you’re running in Safe mode, so if your laptop starts up without any errors, you know that login items are probably to blame.

If your computer starts without problems in Safe Mode, the next step is checking your login items. Restart your MacBook, and list each of the login items it displays for future reference. Then follow this procedure for each item in the login list:

  1. Open System Preferences, click Users & Groups, and then click the Login Items button.
  2. Select and delete the first item in the list.

    You can delete the selected item by clicking the Delete button, which bears a – (minus) sign. If a recurring error message mentions a specific application that appears in the Login Items list, that’s your likely culprit, so start by deleting that item.

  3. Restart your MacBook.
  4. If your laptop is still misbehaving, repeat Steps 2 and 3, and disable a new login item.

    When your MacBook starts up normally, you’ve likely discovered the perpetrator.

  5. Delete and reinstall the problem application.

    Don’t forget to add back each of the working login items to the Login Items list by clicking the Add button, which carries a + (plus) sign!

Step 8: Turn off your screen saver

The next step is turning off your screen saver. This remedy is a long shot, but it isn’t unheard-of to discover that a faulty, bug-ridden screen saver has locked up your MacBook. If you’re running a screen saver other than one from Apple, and your computer never wakes up from sleep or hangs while displaying the screen saver, you’ve found your prime suspect.

Reboot your MacBook (if necessary), open System Preferences, click Desktop & Screen Saver, and click the Screen Saver button. Then do one of the following:

  • Switch to an Apple screen saver.
  • Click the Start After pop-up menu and choose Never.

Step 9: Run System Information

Ouch. You’ve reached the final step, and you still haven’t uncovered the culprit. At this point, you’ve narrowed the possibilities to a serious problem, such as bad hardware or corrupted files in your macOS System folder. Fortunately, Big Sur provides the System Information utility, which displays real-time information on the hardware in your system. To start System Information, follow these steps:

  1. Choose App  ⇒    About This Mac.
  2. Click the System Report button.
  3. Click each of the Hardware categories in turn, double-checking to make sure that everything looks okay.

Remember You don’t have to understand all the technical hieroglyphics to check your system. If a Hardware category doesn’t return what you expect or displays an error message, though, that’s suspicious. If your MacBook doesn’t have a specific type of hardware onboard, such as an optical drive — you won’t see information in that category.

Tip The Diagnostics category shows whether your MacBook passed the Power On self-test.

Okay, I Kicked It, and It Still Won’t Work

Don’t worry, friendly reader. Just because you’ve reached the end of my MacBook Troubleshooting Tree doesn’t mean that you’re out of luck. In the following sections, I discuss the online help available in macOS and on the Apple website, as well as local help in your own town.

Local service, at your service

In case you need to take in your MacBook for service, an Apple Store or Apple Authorized Service Provider is probably in your area. To find the closest service, launch Safari; visit the Apple website Support page (; then click the Apple Repair Options link at the bottom of the page.

Always call your Apple service provider before you lug your (albeit lightweight) laptop all the way to the shop. Make sure that you know your MacBook’s serial number (which you can display in System Information) and which version of macOS you’re using.

The Apple Help Center

Although most macOS owners tend to blow off the Help Center when the troubleshooting gets tough, that’s never the best course of action. Always take a few moments to search the contents of the Help Center by choosing Finder  ⇒    Help to see whether any mention is made of the problem you’ve encountered.

Apple Help online

If you haven’t visited the Apple MacBook Support site yet, run, don’t walk, to There, you’ll find

  • The latest patches, updates, and tutorials for the MacBook line
  • MacBook and macOS discussion boards moderated by Apple
  • Tools for ordering spare parts, checking on your remaining warranty coverage, and searching the Apple knowledge base
  • Do-it-yourself instructions (PDF files) that you can follow to repair or upgrade your MacBook

And Now … Windows?

Okay, I know that this chapter is about what to do if your MacBook misbehaves, so why am I suddenly talking about Windows? That’s a touch of nerd humor on my part, because many diehard Mac fanatics would consider the idea of running Windows on a MacBook to be a big step backward! They’d ask, “Mark, why introduce that misbegotten operating system onto a perfectly good MacBook?”

Well, ignore those naysayers! There’s no need to be furtive about your Windows yearnings. Although I’m an enthusiastic Mac owner, I also own two smooth-running PCs, and all my computers cohabitate quite well in my office. I use Windows 10 every day for several tasks. Also, some PC software simply isn’t available for Macs to run. So, dear reader, what if I told you that macOS Big Sur and Windows 10 can live together in peace and harmony, all on the same internal drive inside your Mac?

In this chapter, I discuss the wonder that is Boot Camp — the free utility included with Big Sur that allows you to install and run Windows on your Intel-based MacBook’s internal drive. I explain how to switch between the two operating systems with a simple reboot.

Remember If you’re using a new MacBook Air or MacBook Pro with the M1 processor, you can stop reading here — the Boot Camp feature in Big Sur will work only with the Intel series of processors. (If you fit into this category, I feel your pain. My latest MacBook Air is equipped with the M1 CPU, and therefore Boot Camp is off-limits to me on that laptop.) You can, however, use a third-party virtual machine application like Parallels Desktop ( to run Windows on an M1-based MacBook.

Hold on to your hat, Intel-based MacBook owners: You’re about to take a wild trip that proves you can indeed have the best of both worlds.

Figuring out how Boot Camp works

First, a bit of technobabble, but I promise that it’ll be over soon, and I’ll try to keep things from getting too boring.

In years past, you may have heard that a Mac computer couldn’t run Windows out of the box without expensive hardware or software and that Mac software was off-limits to PCs … and you’d have heard correctly, at least for all but the last decade or so of the Macintosh computer. The incompatibility was a result of Apple’s using a series of Motorola processors (CPUs) that didn’t speak the same language as the Intel CPUs used in PCs. Consider a person who speaks Korean trying to read a book in Arabic, and you get the general idea.

Then Apple began using Intel processors in Macs, and the ground rules changed. Apple hardware was suddenly compatible with Windows. All that was needed was a bridge to help keep both OSes separate on the same hard drive, and Apple developed Boot Camp. That bridge works only in one direction, of course, because you still can’t run Macintosh software on a PC. (Go figure.)

Boot Camp accomplishes this magic by creating a separate Windows partition on your MacBook’s internal drive. The partition holds all your Windows data, including the OS; your Windows program files; and the documents you create while running Windows. Consider this partition to be separate from your macOS data, even though both partitions exist on the same physical internal drive.

Think of it this way: Rebooting your MacBook with Boot Camp is similar to changing the station on an FM radio. The hardware is the same, but you switch to a different station (Windows instead of macOS), and you’re listening to different music (country instead of rock). How’s that for a comparison, Dr. Science?

Naturally, you need free space on your MacBook’s internal drive to install Boot Camp. Apple recommends having 40GB of free space, but I’d bump that up to 80GB.

Warning When your MacBook is running Windows, it’s just as susceptible to virus and spyware attacks as any other Windows PC. Make sure to invest in quality antivirus and antispyware protection for your Windows side!

Warning Remember what I said about Boot Camp modifying your internal drive? Do not install Boot Camp without backing up your existing data on your MacBook’s internal drive! I’ve never had a problem with Boot Camp, but there’s always a first time. In case of catastrophe, you can always use your Time Machine backup to restore your MacBook’s operating system and all your data — another good reason for you to pick up an external drive and use Time Machine on your Mac laptop. Back up, brothers and sisters; back up!

Configuring Boot Camp

Installing Boot Camp is surprisingly easy and takes far less time than it takes to install Windows afterward. Follow these steps:

  1. Launch the Boot Camp Assistant.

    You can find the Assistant in your Utilities folder, which is in your Applications folder. I use Spotlight to reach it quickly: Click the Spotlight icon on the Finder menu bar, type Boot Camp in the search box, and then click the Boot Camp Assistant entry in the Spotlight results list.

    Tip Click the Open Boot Camp Help button on the introduction screen for additional tips and documentation that cover the Boot Camp setup process. (You can also print any part of Boot Camp Help, which makes for handy documentation in case you have questions about running Windows that aren’t covered in this section.)

  2. Click Continue on the introduction screen.

    The Boot Camp Assistant Install Windows screen appears.

  3. Choose the location of the Windows Install ISO file and the size of your Windows partition, and click Install.

    To resize the Windows partition, click and drag the divider that separates the Windows partition from the macOS partition. Again, you can devote more drive space to your Windows partition than the amount recommended by the assistant, but don’t forget this important fact: What you reserve for use in Windows can’t be used by macOS Big Sur! Therefore, I always suggest a conservative amount. (In other words, don’t devote 300GB of your 500GB drive to your Windows partition, because you’ll cramp your style in macOS.)

  4. Reboot, if required.

    You may be prompted to launch the assistant again.

  5. Click Start the Windows Installer and then click Continue.

    From this point on, you’re running the Windows installation program just as you would be if you were using a PC. (Well, actually you are using a PC now — temporarily, anyway.)

  6. Follow the onscreen prompts, which differ for each version of Windows.

Remember When you’re prompted by the Windows Installer to choose the partition to format, choose the partition named BOOTCAMP. Formatting any other partition will likely result in the loss of all your macOS files and data. (Again, this is why you should always back up your existing system before putting Boot Camp to work.)

After Windows is installed, it should automatically run the Boot Camp driver installation program for you. When the drivers are in place, you’re ready to do the Microsoft dance.

Tip Are you moving your stuff from Windows (running on your old PC) to … well, Windows (running on your Mac)? Brings an entirely new meaning to the term switcher, doesn’t it? If so, you can copy the files and folders on your existing PC directly to Windows running on your Mac by using the Windows Easy Transfer utility.

Switching to Windows

Here are three methods for switching back and forth between your macOS partition and your Windows partition:

  • From macOS Big Sur: To restart your Mac in Windows, click System Preferences on the Dock and then click the Startup Disk icon. Click the Windows partition you created in the list to select it. (The folder icon bears the Windows logo, and it’s labeled Windows as well.) Click Restart, and click Restart again when you’re asked for confirmation. Your Mac reboots and loads Windows, and it continues to run Windows when started or rebooted until you follow one of the next two methods of returning to macOS.
  • From Windows: Right-click the Boot Camp icon in the notification area at the right side of your Windows taskbar — it looks like a diamond — and choose Restart in macOS from the shortcut menu. Again, you’ll be asked to confirm your choice. When you click OK, your MacBook reboots and returns to Big Sur.
  • During the boot process: Need a temporary fix from your other OS? You can reboot from Big Sur or Windows and hold down the Option key when you see the Apple logo. Your MacBook displays a nifty row of icons, each representing a bootable OS that you can use. To boot macOS, click the Big Sur partition icon. To choose Windows, click the Windows partition icon. Note that when you turn on or reboot your Mac, it returns to the OS you last selected in the System Preferences Startup Disk pane.
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