To answer your questions in the most simple way possible:
Disk operationg system DOS is a computer operating system using line instruction. For a computer system uses disk drive as secondary memory. A Windows system is a computer operating system with Graphic User Interface GUI instead of line instruction.
Disk Operating System is over with. It's extinct.You can still use a dos/type environment called Command Prompt (NOT THE SAME) .Windows provides a graphic user interface (GUI) which utilizes a mouse/icons/etc.