I have been really curious on the subject of operating system. Since I left my school days before I hit this subject, I suppose I can just learn this by myself. Couple of days ago I took the course on Udacity, tought by lecturers from University of Georgia, which also available on Youtube, for free.
Operating system sounds really fancy. But it turns out to be just another computer program like those we as a software engineer build day to day.
What differ is the purpose.
Operating system is a program that manages other programs.
It manages how each of our program uses the available resources such as the disk, memory, or processor.
It provide isolation and protection among applications, and hides hardware complexities through system calls (sort of API of using your hardware on behalf of the OS).
Examples of operating systems are Mac OS and Linux, which both are Unix-based. Other forms might include Android, iOS, and Symbian on embedded platforms.