[rogerbinns]

They were not competing. Microsoft has always put phenomenal effort into backwards compatibility. Windows was constrained to work with DOS, your DOS device drivers, and most importantly your DOS apps. The majority of initial PC buyers were businesses, and those apps mattered. The last time I tried, the MSDOS 1.0 version of Visicalc (1982) still ran under Windows.

By contrast the Mac didn't provide any Apple 2 backwards compatibility (although I believe one Mac model had an add on board, and there was the IIgs). Windows and the Mac were competing in different dimensions (backwards compatible, hardware & software variety versus green field new platform).

TopView - https://en.wikipedia.org/wiki/IBM_TopView - GEM https://en.wikipedia.org/wiki/Graphical_Environment_Manager - and to a lesser extent Desqview and similar were the competition for Windows, until later OS/2 was as well.