Also known as UNIX, though the letters do not stand for anything. The Unix operating system was first created in Bell Labs way back in the 1960s. It became popular in the 1970s for high-level computing, but not on the consumer level. Since a lot of Internet services were originally hosted on Unix machines, the platform gained tremendous popularity in the 1990s. It still leads the industry as the most common operating system for Web servers.
Still, Unix remains somewhat of an ambiguous operating system, as there are many different versions of it. Some examples include Ultrix, Xenix, Linux, and GNU, which, making things even more confusing, all run on a number of different hardware platforms. Most people do not ever need to use Unix, but computer geeks seem to have the need to use it as much as possible.