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macOS User Guide
- Welcome
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- Work across devices using Continuity
- Use iPhone as a webcam
- Use iPhone with Desk View
- Stream audio and video with AirPlay
- Use one keyboard and mouse to control Mac and iPad
- Hand off between devices
- Unlock your Mac with Apple Watch
- Make and receive phone calls on your Mac
- Sync music, books, and more between devices
- Resources for your Mac
- Resources for your Apple devices
- Copyright
If you can’t install macOS on an external disk
You can install macOS only on disks with the GUID Partition Table scheme. Use Disk Utility to check your external disk’s partition scheme to make sure it’s the required scheme.
In the Disk Utility app
on your Mac, choose View > Show All Devices (a checkmark indicates it’s selected).Select the external disk in the list on the left.
Disks appear flush left in the list (volumes are indented below disks).
On the right, check if the description below the disk name mentions GUID Partition Map.
If it doesn’t, you need to reformat the external disk before you can install macOS on it. For information about reformatting an external disk using Disk Utility on Mac, see Erase and reformat a storage device.
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