Opinions seem to vary a little on the birthday of Windows. Charles Petzold says the files are dated November 15th, 1985. Ray Ozzie says it's the 20th. ComputerWorld says the 20th also.
Whatever you think the date should be, you really need to read the article by Charles. He did a keynote "selling" Windows 1.0 (a product almost none of us used) as a solution to the problems of the day:
Will it spoil the gentle humour throughout the piece, written 5 years ago, if I show you the output of his demo? I think not:
And that is Windows, and I don’t know about you, but after this event is over,
I’m going home and writing me some Windows apps.
I'm with you, man.