How to Boot from an External HDD or SSD: Step-by-Step Guide

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A step-by-step guide making your PC or Mac boot from USB
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This wikiHow teaches you how to have your computer boot from an attached external hard drive rather than from its built-in hard drive. Doing so is useful when attempting to run a different operating system (e.g., Linux) or install a tool that requires your built-in hard drive to be inactive. Continue reading to learn more.

Quickly Boot from an External Drive

On Windows, go into the BIOS, locate the "Boot Order" section, and make the external drive the first in the boot order. On a Mac, restart your computer, press Opt as the logo appears, then choose the drive you want to boot from.

Section 1 of 3:

Setting up Your External Hard Drive

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  1. Skip this step on Mac. If you can't boot into Windows, or you want to set your computer to boot from an external hard drive, you'll need to access the BIOS , which is a control panel that you open by repeatedly pressing a key (usually a function key such as F12 ) as your computer starts up. [1]
  2. Plug one end of the external hard drive's USB cable into a free USB port on your computer, then plug the other end of the cable into the external hard drive.
    • The external hard drive will usually have an indicator light that blinks slowly or stays constant when your drive is connected.
    • If your PC or Mac doesn't have a port that matches the USB cable on your external drive, you may need to buy an adapter. For example, if your Mac doesn't have a USB 3.0 (rectangular) port, you can buy a USB-A to USB-C or Thunderbolt-3 adapter.
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  3. If the external hard drive isn't compatible with your computer out of the box, you may encounter an error message stating that the drive is corrupted or otherwise unreadable. Formatting the drive for your computer's file system ( NTFS for Windows and Apple File System (APFS) for Mac) will allow you to access the drive. [2] [3]
    • When formatting the drive, you can choose exFAT as the file system to make the drive accessible to both Windows and Mac computers.
    • Depending on the type of data you plan on putting on the drive, you may have to format it again later. For example, using the Live Linux tool to burn a Linux Disc Image to the external hard drive will automatically format it again.
    • Formatting will erase any data that's already on the drive.
  4. You can't boot from an empty hard drive; in most cases, booting from a hard drive will require you to have a disc Image (abbreviated to " ISO ") file on the hard drive. Examples of ISO files include the ones used to install Linux and Windows.
  5. You can usually do this by dragging the ISO file (or other file, if different) into the external hard drive's window and dropping it there.
    • If you're using a program such as the Windows 10 installation tool or LiveLinux to create your bootable external drive, skip this step.
  6. The final step before you can boot from your external drive is to tell your computer to view it as bootable. You can use Command Prompt (Windows) or Terminal (Mac) to do so. [4]
    • If you're using a program such as LiveLinux to burn an ISO file onto the external hard drive, the hard drive will be made bootable in the process.
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Section 2 of 3:

Booting from an External Hard Drive on Windows

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  1. Your external HDD or SSD's cable should be connected firmly to both your computer and the external hard drive, and the external hard drive should be in a position where it doesn't create any tension on the cable.
  2. In the Start menu, press the "Power" icon, then select Restart . You'll need to press the BIOS key as your computer restarts.
    • You can also start BIOS in Windows by going to Settings > Update & Security > Recovery > Restart now > Troubleshoot > Advanced > UEFI Firmware Settings > Restart . [5]
  3. As soon as your computer's screen turns off, you'll need to begin pressing repeatedly the key specified by your computer's manufacturer.
    • Here are some of the most common BIOS keys:
      • Acer: F2 or DEL
      • ASUS: F2 or DEL
      • Dell: F2 or F12
      • HP: ESC or F10
      • Lenovo: F2 or Fn + F2
      • MSI: DEL
  4. The BIOS is usually a minimal interface with white or colored letters on a blue or black background.
  5. Scroll over to the "Boot Order" tab using the right arrow key, or look for the "Boot Order" option in one of the menus on the main page if you don't see a "Boot Order" tab.
    • You may first need to select an Advanced tab to see the "Boot Order" menu.
    • The BIOS menu varies from PC to PC, so don't be afraid to look around for the "Boot Order" section.
  6. Find your external hard drive's name or classification (e.g., External Hard Drive ) in the "Boot Order" list, then press the "Down" arrow key until the external hard drive is selected.
    • In some cases, you'll only be able to select USB devices (or similar) in this menu. If so, make sure that your external hard drive is the only USB storage attached to your computer when booting from it.
  7. Since it's a USB drive, you'll usually want to look for "USB" or "Removable Devices." Press the "Move Up" key (usually the + key) as specified by the key legend on the right side of the screen until your hard drive's name is at the top of the "Boot Order" list.
    • In some cases, the key legend will be at the bottom of the screen instead.
  8. Usually, you'll press a key to do this, so check the key legend for a "Save and Exit" option.
    • You may need to confirm this step by pressing another key.
  9. Once your external hard drive is selected as the boot location, your boot program or service will open; follow the on-screen prompts to open, install, or set up the program or service. [6]
    • For example, if you're installing Linux, you'll be asked to select a language and country, enter your user information, and so on.
    • If you already have an operating system installed and set up on the external hard drive, completing the BIOS setup will open the operating system.
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Section 3 of 3:

Booting from an External Hard Drive on Mac

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  1. Your external drive's cable should be connected firmly to both your computer and the external hard drive, and the external hard drive should be in a position where it doesn't create any tension on the cable.
    • If you can't see your external disk in Finder, go to Finder > Settings and make sure External disks is checked. If it has a line through it instead, your disks won't display even if they are connected.
  2. It's in the drop-down menu.
  3. Your Mac will begin to restart.
  4. Once your Mac's screen goes black, you can start holding down the ⌥ Option key.
  5. You'll do this until the Startup Manager window opens.
  6. This window, which will appear in the middle of the screen, will have a list of your available boot locations.
  7. Click your external drive's name in the Startup Manager window. [7]
  8. Click the upward-facing arrow below the external drive. Doing so will prompt your Mac to begin booting from the external hard drive. [8]
  9. Once your external hard drive is selected as the boot location, your boot program or service will open; follow the on-screen prompts to open, install, or set up the program or service.
    • For example, if you're installing Linux, you'll be asked to select a language and country, enter your user information, and so on.
    • If you already have an operating system installed and set up on the external hard drive, confirming your hard drive selection will open the operating system.
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Community Q&A

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  • Question
    Does my hard drive need to have an OS installed on it?
    Community Answer
    Yes, an OS is required to boot from an external hard drive.
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  • Question
    Will my computer boot normally when the hard drive is not connected?
    Community Answer
    No; the hard drive contains the OS files required.
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      Tips

      • If you want your Mac to start from your external hard drive by default rather than just once, open System Settings, click General > Startup Disk , click the lock icon, and enter your login information, select your external hard drive, and click Restart... . [9]
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      Warnings

      • Unplugging your external hard drive from your computer while booting from it will cause your computer to crash.
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      References

      1. ↑ https://www.freecodecamp.org/news/how-to-get-into-bios-in-windows-10-bios-setup-pc-guide/
      2. ↑ https://support.apple.com/en-sa/guide/disk-utility/dsku19ed921c/22.6/mac/15.0
      3. ↑ https://support.microsoft.com/en-us/windows/create-and-format-a-hard-disk-partition-bbb8e185-1bda-ecd1-3465-c9728f7d7d2e
      4. ↑ https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/install-windows-from-a-usb-flash-drive?view=windows-11
      5. ↑ https://www.hp.com/us-en/shop/tech-takes/how-to-enter-bios-setup-windows-pcs
      6. ↑ https://www.pcmag.com/how-to/how-to-run-windows-10-from-a-usb-drive
      7. ↑ https://support.apple.com/guide/mac-help/change-your-mac-startup-disk-mchlp1034/mac
      8. ↑ https://support.apple.com/en-us/HT201372
      9. ↑ https://support.apple.com/en-us/HT202796

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