My Mac won’t boot from a properly created boot disk

Have you ever tried to boot your Mac from a startup disk and haven’t been able to? This may be due to different reasons and throughout the following article I want to show you the most common, at least, in the most recent generations of Macs: those with a T2 chip that correspond to computers that integrate Intel processors with Touch ID and Touch Bar and also on Macs with an M1 chip, that is, computers with Apple Silicon processors.

In the first case, the reason is usually a protection system that is active by default and that does not allow the Mac to boot from a drive other than the one integrated into the computer itself . This protection system can be deactivated as you will see a little below and it is necessary to do so in order to start with the external unit. In the second case, on Mac with M1 chip, the reason is usually an incorrect use of the keyboard shortcut necessary to boot from a different drive than the usual one.

Allow an Intel-based Mac to boot from an external drive

As I said, in the case of Mac computers with an Intel processor and T2 chip, those that include Touch ID, the process involves deactivating a boot security option that by default is always active. To do this you just have to follow these steps:

1. With the Mac off, press the power button and quickly press the Command + R key combination to enter recovery mode.
2. Open the Utilities menu and then select the Startup Security Utility option.
3. In the new window, go to the External boot section and check the “Allow boot from external media” box.
4. Restart your Mac and hold down the Option (Alt) button during startup to allow your computer to select the drive you want to boot from (of course remember to have the external drive connected at the time of reboot).

Once you have taken these steps, you should have no problem booting your Mac with an external drive that contains an operating system installation disc or any other type of software that works during computer startup.

Booting a Mac with an M1 chip from external media

In the case of Macs with the new M1 processors developed by Apple, the process of booting with an external drive is done differently from computers that mount Intel chips. In this case, the start-up is carried out in the following way:

1. With the Mac off, press and hold the power button until the screen with the startup options appears. Of course, it is important that you have the external drive connected to the computer.
2. Select the external drive from which you want to start the computer and click on Continue.

And that’s all. In this case, it is not necessary to deactivate any security system, although as you have seen the process is different from the one followed in computers with Intel processors .

After following these steps you should have no problem starting your Mac with an external startup disk. If you are still having problems, it is likely that the startup disk is not created correctly or that there is some other problem related to the external drive.