Install Windows 10 on external hard drive.. but [duplicate]

I need to run Visual Studio on my MacBook Pro and I need Windows to do that. The easiest and well known way to install Windows on a Mac is by running the Boot Camp app on the Mac and let it do what's necessary. The problem is that I don't want to partition the Internal SSD so the remaining option is to install Boot Camp Windows 10 on an External Drive and boot it every time I need it by plugging in my external USB 3.0 HDD. Is this achievable?

Here's an updated procedure for Windows 10, based on orkoden's excellent answer.

I tested this process on a MacBookPro11,1 running OS X 10.11.5 (15F34). Throughout the process, directly connect all devices to your Mac. I found that certain operations failed more frequently if I used the USB hub in my monitor.

In addition to the external drive that will host your Windows installation (the "destination drive"), you will need another USB drive (the "driver drive") to temporarily store the Boot Camp drivers.

I used these parts:

• Destination drive: Samsung T3 Portable 500GB USB 3.0 External SSD (MU-PT500B/AM)
• Driver drive: SanDisk Extreme 32GB USB 3.0 Flash Drive (SDCZ80-032G-GAM46)

Here are the steps:

1. Install VMware Fusion 8.1.1 from VMware's site
2. The non-professional free evaluation version is sufficient
3. VMware Fusion 7.1.3 couldn’t connect my external USB disk to my Windows VM
4. I downloaded VMware-Fusion-8.1.1-3771013.dmg (SHA256: 29cad381a36374e58a85fb58f7aaad8cae41ad50ef07fdda0db6d782c95c0a95)
5. Download the Windows 10 ISO file from https://www.microsoft.com/en-us/software-download/windows10ISO
6. I chose Windows 10, English, 64-bit
7. I downloaded Win10_1511_1_English_x64.iso (SHA256: cf5cff9e23c853fed769cf382e18b29889dcc0055b69226f0164ab51eca3069c)
8. Download the Windows 7 Automated Installation Kit from https://www.microsoft.com/en-us/download/details.aspx?id=5753
9. I downloaded KB3AIK_EN.iso (SHA256: c6639424b2cebabff3e851913e5f56410f28184bbdb648d5f86c05d93a4cebba)
10. Prepare the driver drive.
    1. Run diskutil list to determine the device name. In my case, the device name was /dev/disk2.
    2. Erase the disk using diskutil eraseDisk fat32 DRIVERS MBR /dev/disk2
    3. Open Boot Camp Assistant
       1. In "Introduction", click "Continue"
       2. In "Select Tasks":
          1. Uncheck "Create a Windows 7 or later version install disk"
          2. Check "Download the latest Windows support software from Apple"
          3. Uncheck "Install Windows 7 or later version"
          4. Click "Continue"
       3. If "Select Tasks" is not there, try "Action->Download Windows Support Software".
       4. In "Save Windows Support Software", choose the driver drive, and click "Continue".
       5. Wait for the process to complete.
    4. Eject the driver drive: diskutil eject /dev/disk2
    5. Disconnect the driver drive.
11. Prepare the temporary Windows VM. We’ll use the temporary Windows VM to write the disk image to the destination drive. In VMware Fusion:
12. Create a new VM:
    1. File > New
    2. In "Select the Installation Method", choose "Install from disc or image", and click "Continue".
    3. In "Create a New Virtual Machine", choose "Use another disc or disc image…", locate Win10_1511_1_English_x64.iso, and click "Continue".
    4. In "Microsoft Windows Easy Install", uncheck "Use Easy Install", and click "Continue".
    5. Click "Finish".
13. Start the VM and complete Windows Setup. The settings don’t really matter, because we’re just using this VM to write the disk image.
    1. Choose "Next"
    2. Choose "Install now"
    3. Choose "I don’t have a product key"
    4. Choose "Windows 10 Pro"
    5. Choose "I accept the license terms"
    6. Choose "Custom: Install Windows only (advanced)"
    7. Choose "Drive 0 Unallocated Space" and click "Next"
    8. Choose "Use Express settings"
    9. Choose "I own it"
    10. Choose "Skip this step"
    11. Enter a username
14. Install the Automated Installation Kit:
    1. From the "Virtual Machine" menu, choose "CD/DVD (SATA)" > "Choose Disc or Disc Image...". Select KB3AIK_EN.iso.
    2. From the Start menu, choose "File Explorer", and then "This PC". Double-click "DVD Drive (D:) KB3AIK_EN".
    3. Choose "Yes"
    4. Choose ".NET Framework Setup"
       1. Choose "Download and install this feature"
       2. After installation completes, choose "Close"
    5. Choose "Windows AIK Setup"
       1. Choose "Next"
       2. Choose "I agree"
       3. Choose "Next"
       4. Choose "Next"
       5. After installation completes, choose "Close"
15. Prepare and image the destination drive:
    1. From the Start menu, choose "All apps". Choose "Microsoft Windows AIK". Right-click "Deployment Tools Command Prompt". Choose "More", then choose "Run as administrator". Choose "Yes".
    2. Prepare the destination drive:
       1. Run diskpart
       2. Plug in the destination drive. In the "Choose where you would like to connect " prompt, choose "Connect to Windows"
       3. Run list disk to determine the disk number of the destination drive. In my case, the disk number was 1.
       4. Run: select disk 1
       5. Run: clean
       6. Run: create partition primary
       7. Run: format fs=ntfs quick
       8. Run: assign
       9. Run: active
       10. Run: list volume
       11. Note the drive letter for the selected volume (marked with a *); this is the drive letter of the destination drive. In my case, the letter was "E".
       12. Run: exit
    3. Image the destination drive:
       1. From the "Virtual Machine" menu, choose "CD/DVD (SATA)" > "Choose Disc or Disc Image...". Select Win10_1511_1_English_x64.iso.
       2. Run: imagex /check /verify /apply d:\sources\install.wim "Windows 10 Home" e:
          • For Windows 10 Pro, use "Windows 10 Pro"
          • For Windows 10 Education, use "Windows 10 Education Retail Technical Preview"
       3. Run: bcdboot e:\windows /v /s e:
       4. Run: shutdown /p
       5. Quit VMware Fusion
16. Restart into Windows to complete installation
    1. Restart the Mac while holding the Option key
    2. When the startup disk list appears, use the arrow keys to choose Windows. Complete Windows Setup. If Windows restarts during Setup, restart again while holding the Option key to return to Windows.
    3. Insert the driver drive. Open the Start menu, choose “File Explorer”, choose “DRIVERS (E:)”, open the “BootCamp” folder, and open “Setup”. Complete the installation.

Windows is now installed and ready.

• To restart into OS X, click the Boot Camp icon in the notification area and choose “Restart in OS X…”.
• To restart into Windows, open “System Preferences” from the Apple menu, choose “Startup Disk”, choose “BOOTCAMP”, and then choose “Restart…”.
• To choose an OS at boot time, hold down the Option key.

Yes, you can do it. The instructions are originally for Windows 8. Some terminal commands might be a little different for Windows 10.

You will need :

1. Windows 10 x64 ISO file
2. a running Windows installation real or virtualised
3. a blank external hard drive
4. Apple Bootcamp drivers (obtained from the BootCamp setup) on USB key
5. Microsoft AIK

Format and prepare external drive

1. launch the CMD line tool (click on the Start menu, in the search bar type CMD, then launch it)
2. type DISKPART
3. type LIST DISK It will list all drives (DISK 0 ; DISK 1; DISK # ; etc...)
4. Choose the disk you want Windows installed onto and type accordingly SELECT DISK # (# being the number of the disk you want to use (e.g. SELECT DISK 2)
5. Type LIST DISK again, and you will see a * in front of the disk to be erased.
6. Type CLEAN
7. Type CREATE PARTITION PRIMARY
8. Type SELECT PARTITION 1
9. Type ACTIVE
10. Type FORMAT FS=NTFS QUICK
11. Type ASSIGN
12. Type EXIT or close the window

Install Windows with AIK

1. install AIK
2. Mount the Windows 10 ISO image as a drive. VMWare etc. can do that, otherwise use a tool like PowerISO.

3. Note your drives letters before proceeding. Change the letters for your system accordingly. - Drive letter for Windows ISO? Here E: - Drive letter for empty hard drive? Here G:

4. Open CMD tool as an Administrator: click on the Start menu, type CMD, right click and select Run as Administrator

5. Type C:\Program Files\Windows AIK\Tools\Amd64\imagex.exe /APPLY E:\sources\install.esd 1 G:\ (change the letters to fit your setup)
6. Make the USB Drive Bootable. Type BCDBOOT G:\WINDOWS /S G:

First boot and driver installation

1. Plug the external hard drive into your Mac.
2. Start your Mac and hold the ALT (⎇) key to choose the Windows Drive you just installed.
3. Windows will boot, and then will reboot the computer. At the boot chime hold ALT key and again choose the Windows drive.
4. Once on the Windows desktop appears, plug in your Apple Windows Drivers USB keydrive and install the Bootcamp drivers.

After the installation, reboot Windows. Hold ALT again at startup to choose the Windows drive.

Process for 2015- MacBooks (EFI installation)

You will need access to a working Windows 10 installation. See other answers to install a virtual machine.

In Mac OS:

1. Run Boot Camp Assistant to put the Windows drivers onto a separate USB stick
2. Download a Windows 10 x64 ISO
3. Transfer the ISO to your Windows installation.

In Windows:

1. Install Windows ADK, uncheck all alternatives except "Deployment Tools"
2. Double click the Windows ISO to mount it as a drive
3. Plug in the external USB drive.
4. Open an elevated command prompt and run the following:

Find Index Number:

dism /get-wiminfo /wimfile:d:\sources\install.wim

(Find the Windows version you want and remember the index number, we'll use this later.)

Formatting the drive:

diskpart
list disk
select disk 1 (the id of your external drive)
clean (warning: this will erase everything on the drive)
convert gpt
create partition efi size=200
format quick fs=fat32
assign letter=s
create partition msr size=16
create partition primary
format quick fs=ntfs
assign letter=w
exit

Installing Windows:

dism /apply-image /imagefile:D:\sources\install.wim /index:8 /ApplyDir:W:\ /CheckIntegrity 

(D is the letter of the windows installation drive, W is the external drive's NTFS partition, Use the index number you found above to choose the right version of Windows. For me, 8 was for Pro and 3 was for Home)

Installing boot files:

bcdboot W:\Windows /s S: /f UEFI

(S is the external drive EFI boot partition)

Done! Plug the drive into your Mac and restart holding down the Option key and you should see EFI Boot as an alternative, this is your Windows 10 installation.

Final step is to install the Boot Camp Windows drivers. Run setup.exe from the USB drive.