I don't mean to be so dismissive but you kidding me right?
IBM and Microsoft signed an contract, that IBM AT clone computers would ship with Microsoft DOS and they would license (and pay for) every-single-copy of it. The openish IBM PC standard allowed for Microsoft to continually expand into their near monopoly on the Business, and Home PC market.
That agreement literally built Microsoft. When they signed that agreement, Microsoft didn't even own the rights to DOS, or had even made an OS. They just licensed a BASIC compiler.
DOS and Windows are not the same thing. One reasonable interpretation of the history is that "Windows" is specifically the point over which Microsoft & IBM diverged, with Windows being the additions/lineage where Microsoft ruled and IBM's formal contributions essentially nil.
In DOS you literally started windows as an application (not MSDOS 1.0). Windows was originally a visual file manager in MSDOS long before it was short hand for an OS/and full window manager we know today.
Yes, but what was IBM's formal involvement in any of those early versions of 'Windows'?
Neither my memory nor the Wikipedia history suggest any formal IBM role in the development of 'Windows' itself, at least not through Windows 3.11. It wasn't a joint project (though I suppose the closeness of the partnership likely meant source/fix/feature sharing behind the scenes).
Then, IBM was formally cooperating with Microsoft on something they thought would be OS/2. To the extent anything co-developed then wound up in Windows NT, that was never IBM's intent. Again, Windows was the Microsoft-controlled branch, not the partnership product.
That would roughly match the assertion by rational-future about which you were dismissive.
At the time, Windows was a GUI shell over DOS. The diverging happened when IBM and Microsoft were working on OS/2, and Microsoft decided to split and develop WinNT.
IBM and Microsoft signed an contract, that IBM AT clone computers would ship with Microsoft DOS and they would license (and pay for) every-single-copy of it. The openish IBM PC standard allowed for Microsoft to continually expand into their near monopoly on the Business, and Home PC market.
That agreement literally built Microsoft. When they signed that agreement, Microsoft didn't even own the rights to DOS, or had even made an OS. They just licensed a BASIC compiler.