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I have followed this guide: https://9to5mac.com/2017/08/31/how-windows-10-mac-boot-camp-external-drive-video/

When I select EFI Boot from my Samsung M3 portable drive it reboots to the boot recovery assistant and asks for my pw to unlock the macOS disk.

This is the second HD I've tried this on, both to the same effect.

The drive is partitioned 75/25 Time Machine / Windows.

Any help is appreciated

  • What is the model/year of your Mac. What version of Windows. – David Anderson Aug 10 '18 at 12:43
  • Hi @DavidAnderson I'm using the following: MacBook Pro (15-inch, 2018) 2.6 GHz Intel Core i7 16 GB 2400 MHz DDR4 Radeon Pro 560X 4096 MB Mac OS Mojave 10.14 Beta (18A353d) Using windows 10 professional, freshly downloaded ISO and new install of VMWare using said ISO – Allen Wixted Aug 11 '18 at 14:38
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When Boot Camp installs Windows 10 on a Mac, any Apple supplied drivers required to boot Windows 10 are automatically included in the driver store during the installation process. There is no outward indication that this takes place. After Windows 10 finishing installing, software including additional drivers are installed. This process is very evident due to output shown on the display.

When watching the video, I did not see any step where the Apple supplied drivers, required to boot Windows 10, were installed to the drivers store. This means the instructions supplied in this video are incomplete.

So you may ask: Why did the example shown the video work? My best guess would be that Windows 10 was installed on an older Mac. Microsoft makes an effort to include in the ISO all the drivers needed to boot an installation of Windows 10 for any Windows 10 compatible computer. For an older Mac, there would be no needed to copy the Apple supplied drivers to drive store, because the required files would already be in the store.

Since your Mac is a 2018 model, the drivers needed to boot may not have been included yet in any Windows 10 ISO file. If this is the case, Windows 10 will not be able to boot.

My best advice would be to not try to use third party software in an effort to trick Windows 10 into booting from an external drive. All the software needed to install to an external drive is already included in the Window 10 ISO file.

If you want to proceed based on the video, then eliminate the use of the VMWare Fusion software. In other words, use Boot Camp to install Windows 10 to your internal drive, then use WinToUSB to transfer to the external drive. You then can remove Windows 10 from the internal drive.

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  • Thanks for the super clear answer David. Will definitely give this a go! very much appreciated – Allen Wixted Sep 10 '18 at 11:47

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