Microsoft released Windows 1.0 on 20 Nov 1985 and it is 25 years now. Microsoft, no doubt is one of the most popular operating systems till date. Even though, many hate Windows for its instability, stolen look and feel etc. Whatever the allegations could be, but Microsoft Windows is a highly successful Operating System. Right from Windows 1.0 till Windows 7, there have been several Windows versions released. Some of them were very successful and others were just flops. Happy 25 Year Anniversary Microsoft! Wish you get better OS like Windows Phone 7!
Source ZDnet UK
Major Windows releases are below. Highly successful versions are Windows 3.1, Windows 95, Windows XP. (Images from Wikipedia)