My understanding is that the original collaboration between Microsoft and IBM was around certain parts of OS/2, not the whole system, so it is plausible that Mi

My understanding is that the original collaboration between Microsoft and IBM was around certain parts of OS/2, not the whole system, so it is plausible that Microsoft worked simultaneously on OS/2 and NT as the book describes. Note that NT is heavily based on the work previously done at Digital on VMS (by people from the same team), so there are some pre-existing foundations there, at least in terms of design principles and ideas. https://en.wikipedia.org/wiki/OS/2 https://en.wikipedia.org/wiki/OS/2 provides a recap of the history but I cannot find details on exactly who did what in that page. And my memory from what I read in the book is fuzzy at this point...