There is a much longer (and more detailed) description of the history of the transition from DOS to Windows: https://www.filfre.net/2018/06/doing-windows-part-1-ms-dos-a...

(That's part 1 out of 9)

It has a slightly different focus: it doesn't mention PIF files, but spends time on the business relationship between IBM and MS. It also discusses OS/2.