Making an ISO image of a hard drive means creating a 1-to-1 backup copy that consists of a .iso file. Here are two ways to do just that.

How do I install Windows on a SSD instead of HDD? To set up Windows on an SSD instead of HDD, connect the SSD and a bootable USB drive with the Windows installation files.

Windows 10 has a concept of a boot folder that gives a logical location for the boot files and that can be confusing if you expect the boot order you set in BIOS to be the final determination.