macOS High Sierra upgrades solid-state drives to Apple File System (APFS). This system currently requires Startup Manager to switch between Windows and macOS. If you choose Restart in OS X from the Windows Boot Camp menu, this message appears: "Could not locate the OS X boot volume."
Follow these steps to boot into macOS or Windows:
- Restart your Mac, then immediately hold down the Option key.
- Release the Option key when you see the Startup Manager window.
- Select your macOS or Windows startup disk, then click the arrow or press Return.
Repeat these steps any time you need to switch between operating systems.
If you use a screen reader
If you use VoiceOver or another screen reader and you need further help switching between Windows and macOS High Sierra, please contact Apple Support.