Install Windows 10 on USB External Hard Disk on MAC/PC

As a matter of fact, Microsoft doesn't allow to install windows on USB external devices. If you try to install Windows on external disk drive, you'll get this error:

Windows cannot be installed to this disk. Setup does not support configuration of or installation to disks connected through a USB or IEEE 1394 port.

 But you can install Windows by creating and configuring custom UEFI/GPT-based partition scheme.

Note: In this tutorial, I'll teach you how to install Windows on UEFI/GPT-based hard drive partition because almost every PC and MACBOOK run on it. BIOS/MBR-based hard drive partition has become obsolete.

Configuring Disk Partitions using Bootable Windows 10 USB

You have to create a Windows RE Tools partition, a system partition, an MSR partition, a Windows partition, and a recovery image partition. The following diagram shows this configuration:

After creating the partitions, you can apply the Windows image on the newly created partitions.

1. Create a windows 10 USB bootable disk and boot from it.
2. Once you're in the Setup program, select your language, time and currency format and input method, and click Next. Click the Install Now button. Enter/Skip your Windows key if prompted, and read and accept the software licence. In the next screen, press "SHIFT+F10" to open command prompt. Also connect your external hard disk.
3. Now type diskpart and create the partition using the following script below:

list disk

select disk x (where x your disk number 0,1,2,3,... and so on)

clean (This will format the whole disk)

convert gpt

create partition primary size=350

format quick fs=ntfs label="Windows RE Tools"

assign letter="T"

set id="de94bba4-06d1-4d40-a16a-bfd50179d6ac"

gpt attributes=0x8000000000000001

create partition efi size=100
** NOTE: For Advanced Format 4Kn drives, change this value to size = 260 **

format quick fs=fat32 label="System"

assign letter="S"

create partition msr size=128

create partition primary size=256000
** NOTE: I've given 250GB Disk space to the drive where windows will be installed, change this value according to your disk size **

format quick fs=ntfs label="Windows"

assign letter="W"

create partition primary size=4096

format quick fs=ntfs label="Recovery Image"

assign letter="R"

set id="de94bba4-06d1-4d40-a16a-bfd50179d6ac"

gpt attributes=0x8000000000000001

**NOTE: I've a 500GB External hard disk and partitioned it accordingly. After this I get an unallocated disk space roughly say 245 GB which I can create a partition here using "create partition primary" or later after Windows installation using Disk Management. **

list volume

exit

Applying Windows, System, and Recovery Partitions by using Deployment Image Servicing and Management(DISM) Tool

Hope you didn't close the command prompt, if yes then again press SHIFT+F10 to open it.

Type C: and press enter.

Type Dir to check if it's your Windows 10 bootable pendrive. If not, use diskpart to verify your pendrive volume letter. list volume command in the above script shows the drive letter of your pendrive.

Now, type the following command in sequence:

md R:\RecoveryImage

copy C:\sources\install.wim R:\RecoveryImage\install.wim

cd X:\Windows\System32

dism /Apply-Image /ImageFile:R:\RecoveryImage\install.wim /Index:1 /ApplyDir:W:\

md T:\Recovery\WindowsRE

copy W:\Windows\System32\Recovery\winre.wim T:\Recovery\WindowsRE\winre.wim

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

W:\Windows\System32\reagentc /setosimage /path R:\RecoverImage /target W:\Windows /index 1

W:\Windows\System32\reagentc /setreimage /path T:\Recovery\WindowsRE /target W:\Windows

That's it! Exit the command prompt and close the Windows installation. Reboot and make sure external hard disk is your first priority on any Windows PC. If on Mac, reboot and keep pressing option/alt key until you get Boot Menu, select the EFI Boot and continue. It will reboot again so make sure to press option/alt key again as soon as the system starts and do the same.
And then after some more minutes you will be greeted to create your account!

Use BootCamp on Macintosh OS X to download drivers for Windows 10 which will be approximately 1.5 GB. Standalone/Offline driver download is not available as of now.  

Boot Camp Assistant

That's all for today! If you stuck at any point, feel free to comment below!