Windows 3.0 (and subsequent in that series) was not an operating system, it was a windowing environment. Remember, it still ran on top of MS-DOS, and it was still effectively single-tasking in that switching tasks paused the previous task.
I remember a frequent help-desk issue from certain users. Once you'd started Windows 3 (on a 386-grade computer IIRC) you could invoke an MS-DOS command prompt from within it, either within a window or full screen. Having started a full screen prompt, the user would then want to return to the windowing environment and so would type "win". This started a second copy of Windows 3 within the first one. I think you could get to about 3 before it stopped working and the plaintive cry for help came. Funnily enough, it was always the same people it kept happening to.
Windows was not a true OS until Windows 95, as I recall the history.
I recall a lot of modifying of the definition of "Operating System" to try to get MS-DOS recognised as being one.