DOS- do windows need it or not?

Hello!
Please, can someone tell me finaly and for ever, if windows (and which versions!) can live without DOS.
Why do we have DOS under cmd then? (what for?)

Many thanks all!

All recent and not so recent versions of Windows actually live without any DOS. All NT-based versions of Windows are full-fledged operating systems on their own and do not need or use the real DOS in any way. This includes NT 4.0, 2000, XP, 2003, Vista, 2008, 7, 2008, 8 and 2012, none of which has any dependence on DOS.

The last version that sits on top of DOS is Me (along with 95 and 98), which uses the bootloader of DOS, a few services from it, and put GUI and its own driver system on top of it, but has no real kernel on its own. It can be though of similar to Win 3X, but with an hybrid core with 32/16 bits code running on it. That desing was long ago discarded in favor of NT system, which uses a real kernel architecture and completely throws away the DOS layer bellow it.

The cmd window is NOT DOS, not at all. It's just a program like everything else that happens to execute OS commands directly and display results in a way that resembles the old DOS way of doing things. It's sort of a "clone" of DOS, attempting to expose the very same commands it has and adding substantial improvements, all that while sitting on top of the NT kernel architecture, as an independent program, not as a core part of the operating system.

A bit of history, back 'in the day' before Windows 95 it was necessary to first install DOS/Disk Operating System then a version of Windows such as 3.1 was installed. DOS was the Operating System, Windows was the Operating Environment or GUI/Graphical User Interface. The last true DOS I used was MS-DOS 6.22 [there were others such as IBM-DOS, PC-DOS, etc.] Win95 was the first to begin merging DOS with the GUI but still could be set up to boot to DOS [7]. Windows NT4 was further from DOS as was Windows 2000. WinME was the last to be for the consumer as Win2000 was more for business. WinXP moved even further from DOS but as has been noted the Command Prompt does much the same as DOS in having DOS commands available but not all of them. Depending upon what I am doing or where I am doing it I will use the Command Prompt a few times each day, especially for checking Network/Internet connectivity.

As mentioned, its not DOS, its a command shell. Some things are better done from a command shell than a GUI. It also lets you run scripts to automat things you want to do.