How to Boot a Mac from a USB Memory Drive

Table of contents:

2024 Author: Samantha Chapman | [email protected]. Last modified: 2023-12-17 09:13

Nowadays optical drives, CD-ROMs and DVDs, are disappearing on modern computers leaving the only option for installing or reinstalling the operating system to use external USB drives. The process of making these memory devices bootable on Mac is quite simple and hassle-free, as long as you dedicate some time and patience to them.

Steps

Step 1. Download the installation file for the version of the operating system you need from the App Store (for example Mac OS X Lion or macOS Sierra)

The most modern versions of the Mac operating system are available for download directly from the App Store.

Step 2. Downloading this type of file may take some time, depending on the speed of your internet connection

Don't worry if the connection drops during the download, the process will automatically resume where it left off as soon as the connection is restored.

Step 3. Make a backup copy of the operating system installation file you downloaded from the Mac App Store and store it on your desktop

Under no circumstances and for no reason should you use the original installation file.

Step 4. Use the backup copy of the operating system installation file to create the bootable USB drive

Step 5. Select the installation file in question with the right mouse button and click on the option "Show package contents"

Step 6. The contents of the installation file you downloaded from the Mac App Store will be displayed in a new dialog box

Step 7. Navigate to the "Contents" folder, then click the "SharedSupport" icon

Step 8. Inside the indicated folder you will find an installation disk image named "InstallESD.dmg"

This is the file you will need to use to create a bootable installation USB drive of the version of the Apple operating system you have chosen (for example OS X Mountain Lion).

Step 9. Click on the magnifying glass icon located on the menu bar and type in the keywords "Disk Utility"

Step 10. Click on the "Disk Utility" icon that appeared in the list of results to start the program

Step 11. Drag the "InstallESD.dmg" file from the folder where it is located inside the white box on the left side of the "Disk Utility" window

The installation file will be imported into the program.

Step 12. Connect the USB drive to the Mac using one of the free ports

Step 13. Wait for the memory drive to be detected and for the corresponding icon to appear on the desktop

Step 14. Select the USB drive from the list displayed within the "Disk Utility" window

Step 15. Click the Initialize button

Step 16. Make sure you partition the drive using the "Mac OS Extended (Journaled)" file system by selecting it from the "Format" drop-down menu in the "Disk Utility" window

Step 17. The default drive name is "Untitled"

If you wish, you can assign any name you like or use the existing one.

Step 18. Click on the Initialize button located in the lower right corner of the window

Step 19. Wait for the USB drive to be formatted and partitioned with the indicated file system

Step 20. Click on the InstallESD.dmg file icon displayed in the left pane of the "Disk Utility" window

Step 21. Click on the Recover tab displayed in the top center of the "Disk Utility window."

The "InstallESD.dmg" file should already be listed in the "Source" field.

Step 22. Drag the USB drive, displayed in the upper left pane of the "Disk Utility" window, to the "Destination" text field

Step 23. Hit the Reset button and wait for the "Disk Utility" app to do its job

This step can take a long time to complete, so please be patient.

Step 24. Close the "Disk Utility" window

You now have a bootable installation USB drive for the version of the operating system you have chosen to use (for example Mac OS X Mountain Lion).

Step 25. Restart the computer on which you want to use the USB drive you just created

Step 26. While your Mac restarts, hold down the ⌥ Option key on your keyboard

Step 27. Select the USB drive from the menu that appears to have it used as a startup disk

Step 28. Congratulations

At this point you can use the USB drive you just created to diagnose the partitions on a Mac, to check the integrity of the OS X or macOS operating system, to upgrade an old version of the Apple operating system with the one on the USB drive or to perform a fresh installation of the operating system on a Mac.

Advice

Use only original software and programs created directly by Apple and downloadable from the Mac App Store.
There are third-party programs produced just for the purpose of creating bootable USB drives for Mac.

Warnings

Always make a backup copy of the operating system installation file before copying it to the external USB drive.
USB boot drives created with a Mac only work on computers made by Apple.
Always back up your entire system using the Time Machine program before performing a fresh installation of the operating system.
Do not disconnect the USB drive from the Mac while the setup process is in progress.

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