Now you are asking a different question - how to boot Windows from an external drive. I don't know if that is possible in general but, if so, it is going to be excruciatingly slow.
Bear in mind that Windows installation not only depend upon the particular hardware that they are installed on (for device drivers), but also are tied to that hardware by licence key and activation. I don't think it would be possible to produce a Windows disk that would boot and run on any computer, let alone an externally connected one.
This sort of thing is possible with Linux.