install windows 8.1 to external disk

Here’s how to install Windows 8 to an external disk on a Mac.

Note that, for reasons that are a bit of a mystery to me, you can’t get the install to work with a USB 3 external HD. However, it’s completely fine to install to a USB 2 HD and then image the drive over to a USB3 one.

  1. Install Virtualbox
  2. Install VirtualBox OracleVM Extension Pack. It’s a separate download.
  3. Pull down the Windows 8.1 VM for VirtualBox from
  4. Extract with The Unarchiver
  5. Import image to VirtualBox
  6. Connect USB HD to Mac
  7. In Disk Utility, partition the USB HD with 1 Partition of “Free Space”.
  8. Unmount USB HD using Disk Utility
  9. Under “ports->USB” add the HD to the VM
  10. Enable USB2 in “ports->USB”
  11. Launch VM
  12. Open compmgmt.msc by typing it into Explorer
  13. Down in Storage Manager, format the unallocated space as an NTFS partition
  14. Install WinToUsb on VM
  15. By hook or by crook, get your Windows 8 ISO inside the virtual machine. In my case I did it over SMB from a fileserver, YMMV.
  16. Run through the WinToUsb setup, choosing the 200MB parition as the EFI partition, and the large NTFS partition as the system partition.
  17. Go brew some coffee, take a walk, etc.
  18. Turn off the Mac
  19. Hold down Option on boot, choose EFI boot
  20. Now you’re running Windows.

If you want to copy over to a USB3 drive:

  1. Launch Disk Utility
  2. Partition your USB3 drive with 1 MS-DOS partition. Make sure the parition table is GUID, not MBR. MBR won’t boot.
  3. Use WinClone to image the old drive. It’s $30 at the time of this writing, but worth it if you’re doing serious Windows work. The image that comes out the other side is tiny, <4GB in my case.
  4. Restore the image onto the new HD.

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