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macOS User Guide
- Welcome
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- Use Continuity across your devices
- Use your iPad as a second display
- Hand off between devices
- Insert photos and scans from iPhone or iPad
- Insert sketches from iPhone or iPad
- Copy and paste between devices
- Use Apple Watch to unlock your Mac and approve requests
- Make and receive phone calls on your Mac
- Control accessories in your home
- Send files between devices with AirDrop
- Use AirPods with your Mac
- Stream content to Apple TV
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- Understand passwords
- Use keychains to store passwords
- Reset your Mac login password
- Set up your Mac to be secure
- Guard your privacy
- Protect your Mac from malware
- Use Sign in with Apple for apps and websites
- Clear your Safari browsing history
- Manage cookies and other website data in Safari
- Find a missing device
- Resources for your Mac
- Resources for your Apple devices
Determine which disk started up your Mac
Some Mac computers can be started up from a CD or DVD, a network volume, a different disk, or another operating system.
Important: If you have an iMac Pro, added security features may be set to prevent the computer from starting up from an external startup disk. See What is the Startup Security Utility?
On your Mac, choose Apple menu
> System Preferences.Click Startup Disk.
Your selected startup disk is shown at the top of the preferences pane.
See alsoChange your Mac startup disk
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