Rufus is a free small tool that enables you to format & create a bootable USB from an ISO image quickly and easily. What is an ISO File?Īn ISO image file or ISO file is an archive file that contains an identical copy (or image) of data & files found on an optical disc (DVD, or CD). Windows ISO file is an archive containing all the required files of the Windows operating system same as a Windows CD or DVD. A bootable USB drive is a simple flash drive containing a Windows ISO file with a boot sector.