The document discusses different types of operating systems including desktop OS, mobile OS, and virtualization. It provides details on the most popular desktop OS such as Windows, Mac OS, Linux, and their versions. It mentions that Windows has 90% of the desktop market. It also discusses features of different mobile OS including Android, iOS, BlackBerry OS, WebOS, and Windows Phone. It provides a brief introduction to Linux, UNIX, and virtualization explaining how a single computer can run multiple guest OS.