## 2.1 Some basic questions you should think about

1. What are the fundamental differences between Windows, Linux, UNIX and OS X operating systems?
2. Why doesn’t a program on one operating system run on another?
3. What about platform-independent applications such as Java or HTML?
4. What is the difference between a .png and .jpg file?
5. Is one better than the other?
6. What is the difference between a .txt and .xlsx file?