What are the important ways in which windows operating system is different from DOS?

Windows is a multi-threaded operating system. Multiple threads are executed on time sharing basis. Thus while one activity is going on in a window another activity may appear to be going on in another window simultaneously. Windows use graphical user interface. Windows run over the DOS layers.

DOS is a single threaded operating system. Only one activity is done at a time. It uses character user interface. Modern windows support advanced file systems.