How to Boot Camp USB 3.0 External Hard Drive

In this tutorial I will show you how to install Windows 10 onto a USB external hard drive. This can be used as a stand alone bootable windows instillation and if you have a mac a bootable Boot Camp instillation. You will need a Windows PC or virtual machine as well as a Mac if you are wanting to Boot Camp. Before we start, this has only been tested with a USB Hard Drive. This may not work with flash drives.


We are going to get all the tools together first.


  1. On your Mac open Boot Camp Assistant and uncheck Create a Windows 7 or later version install disk. Make sure Download the latest Windows support software from Apple. You will need a 4GB or higher usb drive to download it too.
  2. First you will need to download a Windows 10 ISO. You can do this by going here. Follow the steps to get your specific ISO you need.
  3. When that finishes downloading open the ISO and go to the sources Find the install.wim (If you do not find a install.wim and only find an install.esd follow this to convert the install.esd to an install.wim) and copy and paste it to your desktop. You can delete the ISO. It is no longer needed.

Switch to Windows. This can be a virtual machine or a physical Windows instillation. (I recommend a physical instillation. I had problems with my virtual machine when partitioning.)


  1. Move your wim onto your Windows Desktop and put it on the Desktop for now. We will move it later.


  1. Next you need a tool called imagex.exe. It is a command line tool. To get this you can just click here to download.
  2. Move the wim and imagex.exe onto your C Drive. If you don’t know what that means. Open up File Explorer(that little folder icon you use to get to your documents) and type C:/ into the address bar at the top. The reason we do this is to make it easier to navigate to them while we are in command prompt. You may need to provide administer permission to move them to the C Drive. If this happens press Continue for both.
  3. Plug in your external harddrive.
  4. Open Command Prompt as Administrator. To do this open the start menu and find command prompt and right click on it and click run as administrator.

The next few steps will all be commands in the command prompt. So type each step or copy paste and press enter.

  1. cd C:\ (make sure you do a backslash and not a forward slash backslash is above the enter/return key)
  2. diskpart
  3. list disk This will show you a list of the devices connected to your computer. Find your external hard drive. The easiest way is to find the size of it. Now note the Number next to Disk.
  4. select disk n (where n is the number you noted before.)
  5. clean (this will clean all the partitions of the external hard drive and erase everything)
  6. convert mbr (Master boot record is the partitioning format we will use.)
  7. create partition primary size=350 (This will make a 350MB partition that will be used for booting)
  8. format fs=fat32 quick (this formats the partition to fat32)
  9. active (this makes it bootable)
  10. assign letter=b (this assigns a letter to this partition. If you wish to use another letter swap it with where the b Just make sure note of which letter you used) If Windows gives a popup about a drive, just ignore it.
  11. create partition primary (this will make a partition that uses the rest of the drive.)
  12. format fs=ntfs quick (formats it to ntfs)
  13. assign letter=o (o as in operating system not the number 0. This like the last one we assigned can be changed as well.)
  14. exit (this will exit you from diskpart. Stay in the command prompt though)

This is the moment of truth. You will now deploy the install.wim to the external hard drive.

Before you use imagex make sure you are focused on the C:\ directory. Otherwise it will not be able to find the install.wim file.

cd C:\ (you should have done this in step 9 but just in case I wrote it a second time.)(make sure you do a backslash and not a forward slash backslash is above the enter/return key)

  1. imagex.exe /info C:\install.wim (this is to find the index number of the version you want to install.)
  2. imagex.exe /apply C:\install.wim 1 o: (replace the 1 with the index number you found in the last step.) Be patient this will take a while.
  3. o:\windows\system32\bcdboot o:\windows /f ALL /s b:

Once that finishes you are done on the Windows computer and can close the command prompt and eject and unplug the external hard drive from your Windows machine.

If this ends in an error and you are using Windows 7, it is because Windows 7 doesn’t support the /f ALL command.

For Windows 7 use this: o:\windows\system32\bcdboot o:\windows /s b:

  1. Turn off your Mac.
  2. Plug the external hard drive into your Mac.
  3. Power it on and hold the option
  4. Choose EFI boot when the boot options show up.
  5. Follow the install instructions to install Windows. (It may reboot a couple times during instillation. Make sure to press option at every boot and choose the efi boot to continue the instillation.)
  6. Once Windows is done installing and boots for the first time plug in your usb drive that has the Boot Camp drivers and open the usb and press the setup.exe and follow the install instructions.

If you did it right, you will now have a full Windows instillation on your usb hard drive. Happy Boot Camping!