The document provides an introduction to operating systems. It explains that while users feel in control of their computer, an operating system is actually controlling tasks behind the scenes. Common operating systems include Windows, Mac OS X, Linux and UNIX. The operating system is the first software loaded and is essential, as without it a computer cannot function. Operating systems are now also found on smaller devices like phones and wireless routers, as the computers inside have become powerful enough to run full operating systems and applications. The purpose of an operating system is to organize and control hardware and software to allow devices to operate in a predictable yet flexible manner.