An Operating System is the most important piece of software on your computer. Your OS is always there for you when you need it. We never really think about our OS, it is just there.
What does an Operating system do? It does a lot of tasks!
Computer Operating Systems have come a long ways. For more details see Computer History 101: The Development Of The PC
One of the main parts (if not the only part) of an OS is the kernel. This is a very important part of the OS, so please make sure to read about it. There are also different types of kernels, make sure you understand the differences between each one.
Original webpage by Petersen Gross, modified by William Albritton.