If you download a Windows 10 installer ISO then it's not immediately obvious how to correctly write it to a USB disk.
Microsoft don't make this easy. Frustratingly, the naïve approach of writing the ISO straight to the USB disk will yield something that _does_ boot, but that can't actaully perform a successful installation! And, to make things even harder, there isn't even a proper error message the results in trying to use it. The best you get is being dumped straight into a prompt "A media driver your computer needs is missing..."
So, how to correctly use the Windows 10 ISO to prepare a bootable USB disk?
- Create a partition on the USB disk, and create a FAT32 filesystem upon it
Copy the _contents_ of the ISO filesystem, except for the sources/install.wim file to the FAT32 filesystem: rsync -cai /mnt/CCCOMA_X64FRE_EN-GB_DV9/ /mnt/usb/ --exclude=sources/install.wim
Split the install.wim file into several 'split image' files, each one small enough to be copied to the FAT32 filesystem: wimlib-imagex split /mnt/CCCOMA_X64FRE_EN-GB_DV9/sources/install.wim /mnt/usb/sources/install.swm 4096
Now you can boot off the USB stick and install Windows 10.
Not really all that difficult--just completely undocumented.