Go to "System Preferences", then select "Sartup Disk" in "System" section. You gonna see the list of all available partitions for booting. Select the partition you want.
To reset and erase the memory of a MacBook, you need to first back up your data using Time Machine or another backup method. Then, restart your Mac and hold down Command (⌘) + R immediately after the startup chime to enter Recovery Mode. From there, select "Disk Utility," choose your startup disk (usually named Macintosh HD), and click "Erase." After erasing, exit Disk Utility and choose "Reinstall macOS" to reinstall the operating system.
press on startup to display the bootable disks.
go to disk utility and you have the option to erase there
A folder with a stop sign icon on Mac computers indicates that the system is unable to locate the startup disk or that the disk is not functioning correctly. This may occur due to hardware issues, problems with the operating system, or if the startup disk is not properly set. To resolve this, users can restart the computer and hold down the Option key to select a different startup disk or troubleshoot the disk's health. If the issue persists, further diagnosis or repairs may be necessary.
The fix could be that you are using the wrong startup disk. When you turn your PC or mac on press f1 repeatedly until you come to the startup menu. From this select 'startup' preferences, start up disk and select the right one. If you are unsure there is no harm in trying them all as i doubt you will have more than 2 hard disks.
Restart your computer, then hold the Option (Alt) key as it starts up. Or, use the Startup Disk control panel in Windows or Mac OS X Startup Disk preferences to set the default operating system to use each time the computer starts up.
Built into Mac OS X is an application called Disk Utility, which can format and partition any internal or external volume. It's located in /Applications/Utilities/. Additionally, there are some third-party utilities that can work with partitions on-the-fly: iPartition, DiskWorks, and VolumeWorks all claim to do this.
erase startup-config
In the Applications folder is a folder called Utilities. In the Utilities folder is Disk Utility. Disk Utility will Erase / Partition / Format a hard drive.
Yes you can. Remember if you do this, don't forget to backup your files. Keep your MacBook Air plugged into the charger, and make sure you have an internet connection. Lastly, due your due diligence and research further if you're unsure or unfamiliar about resetting. Once you're ready, go to Apple Menu > Restart. While the Air restarts, hold down the Command and R keys at the same time. Disk Utility should appear, click Continue. You will see a list on the left...select the startup disk, then click Erase. A pop-up menu should appear. Choose Mac OS Extended (journaled). Type a name for your disk, then click Erase. After the disk has erased, choose Disk Utility > Quit Disk Utility. At this point, choose Reinstall Mac OS X and click Continue. Follow the instructions it gives you.
its either a re-writable disk or its not!
The system disk is the partition from which the operating system was loaded at startup.