Described by one of its developers as "a weak pun on Multics" (which was an experimental, time-sharing operating system at Bell Labs in the 1960s), Unix took off in the early 1970s as a general-purpose operating system. Since much of the Internet is hosted on Unix machines, the OS took on a new surge of popularity in the early 1990s.
Unix comes in many flavors--including Xenix, Ultrix, GNU, and Linux--and runs on a variety of platforms, which makes its development a subject of widespread discussion. But the truly great debate involves how to style the word itself: should it have an initial capital (Unix)? Or should it be in all caps (UNIX)? Since the operating system itself is case-sensitive, the debate rages. Bell Labs' implementation of Unix is trademarked in all caps; for the other implementations, it's optional.