What Is the Most Popular Operating System in the World?.
If your answer is Windows, you're plain wrong. It's ITRON, a Japanese real-time OS kernel that can be customized for any small-scale embedded systems. According to LinuxInsider.com, it is used by more than 3 billion microprocessors found in mobile phones, digital cameras, CD players and many other electronic devices including even satellites.
Source: Jan Krikke, LinuxInsider.com, October 15, 2003 [Roland Piquepaille's Technology Trends]