I tried to follow the guide above using a 2013 MacBook Air and a VMware version of Windows 10 but for some reason, the USB drive (an old SSD from an rMBP in an OWC USB-3 enclosure) would not be recognized by the virtual Windows. I finally ended up using an actual PC running Windows 10 and it recognized the drive without problem.Hello all,
Just a quick guide for some people who may want to install Windows in an external drive (USB/TB) in a UEFI environment.
Note: The drive enclosure should support UASP.
Connect external drive to a Windows VM. You must have a Windows VM in VMware/Parallels.
What you need:
install.wim file (obtain this from your Windows ISO)
Open elevated cmd.exe
Note: All commands aren't case sensitive, including pathway to files.
Type list disk
Take note of the disk you want to select
Type select disk 1 (if your disk is Disk 1)
Type convert gpt
Type create partition EFI size=100
Type format quick fs=fat32 label=EFI
Type assign letter=S
Type create partition primary
Type format fs=ntfs quick label=W2G (or any other name you wish for label)
Type assign letter=E
Open up File Explorer. In your C drive, create a new folder named WIN2GO.
Put the install.wim file in this folder
Back in cmd.exe:
Type dism /apply-image /imagefile:C:\WIN2GO\install.wim /index:1 /applydir:E:\ (this process will take quite a while)
Type E:\Windows\System32\bcdboot E:\Windows /s S: /f UEFI
Restart your entire Mac. After the chime, hold down Option and when prompted to select your boot drive, select EFI Boot.
Proceed installation normally.
After installation, install Boot Camp drivers.
Hope it helps.
Note: If you have an install.esd file instead of install.wim, follow the guide here to convert it into a .wim file.
I also had the problem of having an install.esd file instead of an install.wim file.
I tried the program suggested in the intowindows link but I guess it's no longer freeware.
The comments in that same intowindows article mention a different program, ESD2WIM-WIM2ESD, and that one was free and worked.
Just be sure to check your drive letters when following the above guide because the process of converting the install.esd to install.wim will add and remove some virtual drives on its own.
I finished creating the drive on the Windows PC and then moved it to my 2014 rMBP and it option-booted just fine.
Once I had Windows 8 running off of the USB drive I rebooted to OS X and ran Bootcamp Assistant to get the Bootcamp drivers.
Returned to Windows 8 to install the drivers and then did an in-place upgrade to Windows 10 using the save nothing option. That was the longest part of the whole process -- probably took almost 2-hours.
Windows 10 finally booted and I again installed the Bootcamp drivers.
Whole thing probably took around 3-hours.