Windows 3.0 was the first successful operating system that satisfied PC users.  Windows was not a computer but software that ran and organized files.  This is an operating system.  Windows allows multiple programs to run at the same time.  This software helped the PC boom in 90s.  Macintosh sales declined so that by the end of the decade almost 90% of computers were PC. 

The Microsoft corporation became one of the biggest in the world with Bill Gates becoming the riches person ever.  Due to software that PC users could not live without, Microsoft company continues to be the major producer of operating systems in the world.