The definition of UNIX

UNIX is a family of OSes, each being made by a different company or organization but all offering a very similar look and feel. It can not quite be considered non-proprietary, however, as the differences between different vendor's versions can be significant (it is still generally possible to switch from one vendor's UNIX to another without too much effort; today the differences between different UNIXes are similar to the differences between the different MS-Windows; historically there were two different UNIX camps, Berkeley / BSD and AT&T / System V, but the assorted vendors have worked together to minimalize the differences). The free variant Linux is one of the closest things to a current, non-proprietary OS; its development is controlled by a non-profit organization and its distribution is provided by several companies. UNIX is powerful; it is fully multitasking and can do pretty much anything that any OS can do (look to the Hurd if you need a more powerful OS). With power comes complexity, however, and UNIX tends not to be overly friendly to beginners (although those who think UNIX is difficult or cryptic apparently have not used CP/M). Window managers are available for UNIX (running under X-Windows) and once properly configured common operations will be almost as simple on a UNIX machine as on a Mac. Out of all the OSes in current use, UNIX has the greatest range of hardware support. It will run on machines built around many different processors. Lightweight versions of UNIX have been made to run on PDAs, and in the other direction, full featured versions make full advantage of all the resources on large, multi-processor machines. Some different UNIX versions include Solaris, Linux, IRIX, AIX, SunOS, FreeBSD, Digital UNIX, HP-UX, NetBSD, OpenBSD, etc.