What you’ll need:

You’ll need a few things to complete this guide:

A Mac which supports booting from a USB Device (see Apple Support: Mac computers that support Windows 10)

A USB 3.0 SSD similar to the Samsung T1 (a flash storage device will not be fast enough)

A spare USB drive with a minimum of 2GB of storage to copy the Bootcamp Drivers over to Windows.

Basic understanding of VirtualBox and installing Windows.

Download Windows 10 Installation

Windows 10 is available to download from Microsoft and allows a grace period to license the installation. Windows 10 can be purchased from the Microsoft Store.

Click here to access the Windows 10 download page.

Follow the prompts to download Windows 10 installation disk.

The download is 3.7GB so it may take some time, the next steps will prepare your system to install Windows 10 to the USB SSD.

Download Bootcamp Software for Windows 10

Apple offer a prepackaged driver installation for Bootcamp.

Click here to download the Bootcamp 6.0 drivers for Windows 10 via the Apple CDN. (AppleBCUpdate.exe 1.13GB)

Thanks to Reddit user sadalhayat for identifying this link.

Once this has downloaded copy it to a spare USB drive separate from SSD you will be using to install Bootcamp. Save this for later.

Mac OS X cannot write to the Windows drive out of the box. For this reason you will need to use a separate drive to copy the Bootcamp Software into the new Bootcamp Installation.

Install VirtualBox

Are you wondering why VirtualBox is the next step? Don’t worry, we’re taking advantage of the virtualisation technology to kick start the installation of Windows 10.

We will be using VirtualBox to mount the USB drive as a virtual hard disk inside the Virtual Machine. This bypasses the limitations imposed by the Microsoft Installer preventing us from installing Bootcamp the Apple way.

Download and Install VirtualBox

If you don’t already have VirtualBox, it can be downloaded from their website. Once you have downloaded the package, use the installation package to get up and running with VirtualBox.

Identify your USB Drive’s device location

Open up the Terminal and type:

diskutil list

This command will list all the connected drives on your computer. Browse through the list until you find your storage device.

Your result will look similar to this. Read over the type names until you find one that is your USB SSD.

The text highlighted red “/dev/disk2” is the information we need. This information will tell VirtualBox exactly which storage device it needs to access.

Please note this information may be different on your machine. Read the list carefully to match the address of your USB SSD.

Disconnecting Mac OS X from the USB SSD.

Before we connect VirtualBox to our USB SSD you will need to completely unmount the SSD from Mac OS X to allow VirtualBox full access to the USB SSD.

This can be done by searching for Disk Utility in Spotlight then

Choosing the External USB Device Choosing Eject in the top Menu

Create a Virtual Disk mapping to the USB Drive

This is where the magic starts. We will be using VirtualBox to mount the USB SSD as a normal hard disk in order to trick the Windows 10 installer into thinking it is using a normal hard drive.

First we need to create a Virtual Disk File for VirtualBox so it knows what storage device we are accessing.

Below is the command we will be modifying to create the Virtual Disk file

VBoxManage internalcommands createrawvmdk -filename "bootcamp.vmdk" -rawdisk /dev/diskX

You can copy the entire command with the exception of the last part “/dev/diskX” which will need to be changed to the drive number you identified in the previous step.

In my case it is “/dev/disk2”.

Installing Windows 10 to the USB SSD via VirtualBox

Now that we have everything organised we can start the installation of Windows 10 via VirtualBox.

We will need to give VirtualBox elevated permissions to access our handy bootcamp.vmdk file.

In your terminal type:

sudo /Applications/VirtualBox.app/Contents/MacOS/VirtualBox

This will force VirtualBox to run as the root user and have permission to access the USB SSD.

Creating Virtual Machine

In VirtualBox choose “New” and type “Windows 10 Bootcamp” and click Continue.

Change Memory to “512” MB and click Continue.

On the Hard Disk screen choose “Use an existing virtual hard disk file” browse to your home directory and select the newly created “bootstrap.vmdk”.

Installing Bootcamp, from a Virtual Machine

Now that we have scaffolded the Virtual Machine, connected the hard drive and downloaded Windows 10, it is time to install Windows 10 onto our shiny new USB SSD.

Back in VirtualBox we will need to mount the Windows 10 Installation ISO into the virtual DVD drive.

Open the Virtual Machine’s Settings Panel. Select the Storage tab on the top of the Settings Panel. Select the Empty DVD Icon. Select the CD Icon next to the Optical Drive, Choose Virtual Optical Disk File and select the Windows 10 ISO file. Select OK to save the new settings.

Run the Normal Windows 10 Installation

Follow through the standard screens to begin the Windows 10 installation.

Clicking next and agreeing to the terms and conditions is all you really need to do here except for the following points:

When you meet the installation type screen, select “Custom”.

Delete exisitn

When you are asked where to install Windows, just delete any existing partitions and select “Next”.

Don’t worry, Windows can only see the USB SSD drive you assigned by VirtualBox, your Mac’s existing partitions are not accessible here.

Important! Don’t let windows restart!