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

Macos Sierra Installer And Disk Creator

How to Download a Full macOS High Sierra Installer App. Create a bootable installer for macOS and use it forever. This bootable copy will allow you to downgrade from the latest version of macOS Sierra. This article provides you effective methods to help you fix the macOS High Sierra including the latest macOS 10.13.4 update failure, stuck or installation problem without losing any data.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Recoverit

• Complete set of extraction tools
• Cost effective method in comparison to technician's bills
• Intuiting wizard based layout
• Retrieve 550+ file from any category

These advanced steps are primarily for system administrators and others who are familiar with the command line. You don't need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful when you want to install on multiple computers without downloading the installer each time.

What you need to create a bootable installer

• A USB flash drive or other secondary volume, formatted as Mac OS Extended, with at least 12 GB of available storage
• A downloaded installer for macOS Big Sur, Catalina, Mojave, High Sierra or El Capitan

Download macOS

• Download: macOS Big Sur, macOS Catalina, macOS Mojave or macOS High Sierra
  These will be downloaded to your Applications folder as an app named Install macOS [version name]. If the installer opens after downloading, quit it without continuing installation. To get the correct installer, download from a Mac that is using macOS Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators, please download from Apple, not a locally hosted software-update server.
• Download: OS X El Capitan
  This will be downloaded as a disk image named InstallMacOSX.dmg. On a Mac that is compatible with El Capitan, open the disk image and run the installer within, named InstallMacOSX.pkg. It will install an app named Install OS X El Capitan into your Applications folder. You will create the bootable installer from this app, not from the disk image or .pkg installer.

Use the 'createinstallmedia' command in Terminal

1. Connect the USB flash drive or other volume that you're using for the bootable installer.
2. Open Terminal, which is in the Utilities folder of your Applications folder.
3. Type or paste one of the following commands in Terminal. These assume that the installer is in your Applications folder and MyVolume is the name of the USB flash drive or other volume you're using. If it has a different name, replace MyVolume in these commands with the name of your volume.

Big Sur:*

Catalina:*

Mojave:*

High Sierra:*

El Capitan:

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument and installer path, similar to the way this is done in the command for El Capitan.

After typing the command:

1. Press Return to enter the command.
2. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
3. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the volume is erased.
4. After the volume has been erased, you may see an alert stating that Terminal would like to access files on a removable volume. Click OK to allow the copy to proceed.
5. When Terminal says that it's been completed, the volume will have the same name as the installer you downloaded, such as Install macOS Big Sur. You can now quit Terminal and eject the volume.
   

Use the bootable installer

Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

Apple silicon

1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
2. Turn on your Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes and a gear icon labelled Options.
3. Select the volume containing the bootable installer, then click Continue.
4. When the macOS installer opens, follow the onscreen instructions.

Macos Sierra Installer Dmg

Intel processor

1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
2. Press and hold the Option (Alt) ⌥ key immediately after turning on or restarting your Mac.
3. Release the Option key when you see a dark screen showing your bootable volumes.
4. Select the volume containing the bootable installer. Then click the up arrow or press Return.
   If you can't start up from the bootable installer, make sure the External Boot setting in Startup Security Utility is set to allow booting from external media.
5. Choose your language, if prompted.
6. Select Install macOS (or Install OS X) from the Utilities window, then click Continue and follow the onscreen instructions.

Learn more

For more information about the createinstallmedia command and the arguments that you can use with it, make sure the macOS installer is in your Applications folder, then enter the appropriate path in Terminal:

• Big Sur: /Applications/Install macOS Big Sur.app/Contents/Resources/createinstallmedia
• Catalina: /Applications/Install macOS Catalina.app/Contents/Resources/createinstallmedia
• Mojave: /Applications/Install macOS Mojave.app/Contents/Resources/createinstallmedia
• High Sierra: /Applications/Install macOS High Sierra.app/Contents/Resources/createinstallmedia
• El Capitan: /Applications/Install OS X El Capitan.app/Contents/Resources/createinstallmedia

A bootable installer doesn't download macOS from the internet, but it does require an internet connection to get firmware and other information specific to the Mac model.