You can do this through Time Machine, Apple's official backup application, which will copy all your files onto an external drive. Or click Startup Disk and choose a different startup disk.Check out the products mentioned in this article: MacBook Pro (From $1,299.99 at Best Buy) How to wipe a Mac computer with a factory resetīefore anything, if you don't want to lose the files you have saved on your computer, you should back them up.Check your internet connection, such as by choosing an active network from Wi-Fi status menu in the menu bar. Then click Try Again.If your Mac can't connect to the internet, it displays an alert that an internet connection is required. Windows: An alert informs you that you need to install Windows with Boot Camp Assistant.Or click Startup Disk and choose a different startup disk, which your Mac will also attempt to verify.

Click Update to open the macOS installer, which you can use to reinstall macOS on the startup disk.

macOS: An alert informs you that a software update is required to use this startup disk.

Enter your administrator password, then click Unlock to complete the download. If FileVault is enabled while your Mac is attempting to download updated integrity information, you're asked to enter a password to unlock the disk.

This information is unique to your Mac, and it ensures that your Mac starts up from an OS that is trusted by Apple. If the OS is unknown or can't be verified as legitimate, your Mac connects to Apple to download the updated integrity information it needs to verify the OS. This is a level of security previously available only on iOS devices.ĭuring startup, your Mac verifies the integrity of the operating system (OS) on your startup disk to make sure that it's legitimate. Full Security is the default setting, offering the highest level of security.

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