I tried a few ways but only this worked for me:Needed: USB flash drive 8GB or more, Windows iso, VirtualBox + Extension Pack, WinToUSB ( ) and of course the external drive. WinToUSB free works with Windows10 Home. Please read info on their site for other Windows versions.Use Bootcamp Assistant to download the Windows Support files (you might need to click in the menu for Action).Use Disk utility to format the USB flash drive to exFAT and the external drive to GUID HFS+ or FATCopy the Windows iso, Windows Support files and WinToUSB to the USB flash drive and eject.Install VirtualBox and Extension Pack. Start VirtualBox and make a Windows10 virtual machine (VM), be sure the USB port is enabled.Start the Windows VM. Attach the USB flash drive and the external drive that you want Windows on.Copy the files from the flash drive to the VMs desktop.Install WinToUSB. Open WinToUSB and select the Windows iso as source and the external drive as goal. Let WinToUSB do its work. Wait until it says 100% and then (important:) click HOME. Now copy the Windows Support files to the external drive.Close the VM and VirtualBox and reboot. As soon as you hear the startup sound hold the Alt-key until you see the options for startup. Choose the EFI disk.Now you have to install Windows. When finished, open the Windows Support folder and click setup to install the Bootcamp-drivers.Done!
.iso files under 4GB have been removed from most of the posted online sources, including the official Windows download site. As of February 2021, there's only one ISO version available. I had the best luck downloading a free trial of an NFTS emulator for Mac, and formatting the USB drive there. I then followed the instructions on this blog. Using Terminal:
- You can also download Windows 10 as a free download from Microsoft, but you will need a valid Windows 10 product key to activate at some point. I was unable to enter a Windows 7 or 8 product key in the Windows 10 installer (it won't ask if it auto detects Win 7 or 8 previously installed). Be sure to only download Windows 10 from the Microsoft site to avoid malware. -us/software-download/windows10ISO
You'll then be prompted to enter your product key. If you bought the USB Flash drive version the key is a sticker on the back of the credit card in the box. If you bought the download version then your key is in your receipt. If you are using the free downloaded version you'll need to hit the DO THIS LATER button when asked for a product key serial number. If you already have Windows 8 or 7 installed it shouldn't ask you for a product key and if you activate by July 2016 it should be a free purchase. 153554b96e