The next screen should give you a list of options.

Open the Boot Camp Assistant, and then click Continue.

From the Finder, open the Applications folder, and then Utilities.

If your Mac has an optical drive, the option will be either missing or grayed out. Thanks.In macOS, the option to create a Windows flash drive appears only when the computer does not have an optical drive. so You Can have a LOT of fun with other Operationg Systems and if you really dig there are actually a TON of Completely NON UNIX, LINUX, or MS-DOS based Operating Systems u can have fun with. I modified my MAC PRO and it now runs Win98, winXP, Win10, Ubuntu, Zorin64PRO, Android via RemixOS (dead site but still works and I have the files so Message me if you cant find them) and Phoenix. also NEVER delete the EFI or RECOVERY partitions unless you absolutelly know what you are doing. now wait till its done dumping your disk to a Large External Drive as a RAW Image and feel free to mess around. Make an Ubunto 64bit Boot Disk from a USB drive, and use the ( $ sudo dd if=/dev/sdX 'where X is your Internal Disks Location' of=/diretorytoLargeStorageDevice/filename.img bs=4M conv=noerror status=progress ). But, there are always ways out of 'BrickMode' so just make sure to test your setup on a PC. and after you mess around with it for a bit its a whole lot of fun, granted you dont accidentally brick something lol.

Thanks to this post, I learned EVERYTHING I could possibly ever lear about uEFI, Boot Loaders and Boot Code, Linux, Windows, and various other Implimentations of these. I prefer to have just one folder on the USB root drive to dump my personal stuff into (you can have as many sub-folders in there as you desire). Once the boot applications are written you can copy across any folders containing installers, personal files, PC backup images etc. Luckily after the first boot application is written, the Autoformat checkbox is un-ticked. When it is completed, simply click OK add any others you want to include by ticking the appropriate checkbox. The process will start for the first boot application to be written. 4 message boxes will appear in succession: click YES YES YES OK. A warning will appear concerning the NTFS file system, just click OK and continue to browse for the iso image file. Click the three dots and browse for the image file.

Next, in my case since I use Macrium Reflect and Windows8.1, tick the Windows Vista/7/8/10. If you plan to use this on a UEFI boot system then format to FAT32 (but you lose the ability to copy large files). This allows me to copy large files (>4Gb) to the USB drive.

I don't use UEFI in my bios boot options so I format the drive using NTFS. Next tick the checkbox 'Auto format it with FBinst'. First plug the target USB drive into the PC and open the exe for WinSetupFromUSB.

Make usb bootable