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Have you ever thought of carrying your Mac OS on an external device and gain access to it at any time? If the reaction is yes, then you have arrived at the right post. We will be providing you with the information through which you can install macOS High Sierra on an external drive.

Part 1. How to Install macOS High Sierra on the External Drive

Before beginning the process, there are a few requisites that you must meet. You will need an external drive with a minimum capacity of 16 GB, and second, you will need the copy of the macOS High Sierra installer. You can obtain the installer from the App Store by searching for "macOS" and download it to your Mac hard drive.

install macOS high sierra on external hard drive

Step 1: Formatting the External Drive

To allow the external drive to function as the startup disk, you need to format it to Mac OS Extended and employ GUID partition map. Start the utility disk. You can find it under the Applications category or search it using Spotlight.

free up storage space on macOS high sierra

As utility disk runs in the background, you can check for the format of the external drive. In the following example, the drive is in Master Boot Record format. First, unmount the drive. After unmounting, you can select the same drive from the left of the window as shown in the figure below. Now, from the tabs that appear in right window, choose "Erase" option.

check format of hard drive

In the next window, you can now format the external drive as "Mac OS Extended" and opt for GUID Partition Map. If you choose to, you can also give it a name. Press "Erase" to proceed. After completion, you will see the following screen. Press "Done" to proceed.

format external hard drive

Step 2: Installing macOS High Sierra on the External Drive

After you complete the download of the macOS installer, double click the same from the Applications folder to begin the installation procedure. Press "Continue" in the following screen.

download macos installer

Click "Agree" to the accept license agreement. In the next window, press the "Show all disks" option. The window will display the local drive and the connected external drive. Choose the external drive in this case. You will have to key in your system user name and password.

accept license agreement

macOS High Sierra will begin installing on the selected external hard disk. It requires some time to complete the task. You can wait until the process is complete. Before it completes the installation, the Mac will restart. Therefore, it is preferable to save any other work that is in progress.

install macos high sierra

After restarting, the Mac will take a minimum of 15 minutes to complete the installation process. It will then reboot from the new device. You then have to proceed with the general process of activating Siri, time zone, and adding the user account. Once you complete these actions, you will possess the new version of macOS High Sierra on your external drive. Do not remove the external drive, as Mac OS will access the files on the drive periodically. You can now use the same every time you wish to use High Sierra.

istall macos high sierra on external hard drive

Part 2. How to Use macOS High Sierra with the Bootable Hard Drive

As you now have macOS High Sierra in the form of bootable hard drive, you can use it with another compatible Mac or when the situation demands. However, remember that using the external device as a bootable drive will slow down the functioning of the system. More importantly, it is useful only when you are facing trouble with your existing internal drive of the Mac.

The following information will be helpful in case if you choose to use macOS High Sierra with the bootable hard drive:

Step 1: If there is a trouble with the current hard disk, and you wish to solve it or use the new version of the OS, then plug the bootable external drive to the Mac.

Step 2: Power on the machine and hold the option button until you notice the recovery screen appear. From the screen, you can choose the bootable external device that you have created.

Step 3: You will boot into the macOS High Sierra version for that particular session.

install macOS high sierra with bootable hard drive

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