The word UNIX, written in all upper case (i.e., capital) letters, is generally used to refer to those operating systems which use this term as the entirety of or as part of their official names, including all of the original versions of UNIX that were developed at Bell Labs. It is also used to refer to the UNIX trademark.
When UNIX was first developed, it was a common practice for the names of operating systems to consist of all upper case letters, largely because many computer terminals at the time could not produce lower case (i.e., small) letters. Although UNIX was originally written as Unix (i.e., lower case except for the first letter), the name was soon changed to the all-upper case version, where it remains today, to conform to the naming convention of that era.
The use of the word Unix has become increasingly common in recent years, including by some major publishers, as a generic term that refers to all operating systems which incorporate the major features of the early versions of UNIX, whether or not they officially call themselves UNIX or use the UNIX trademark. However, this usage is controversial, and it is not favored by the owners of the UNIX trademark.
The UNIX trademark is owned by The Open Group, an industry consortium that was formed in 1996 from a merger of the Open Software Foundation (OSF) and X/Open Company, Ltd (X/Open). This trademark was acquired by X/Open in 1994 from Novell, Inc., which had purchased it from AT&T (the parent corporation of Bell Labs) the previous year.
Reasons cited by its advocates for the lower case version's growth in popularity include the facts that it supposedly looks better and is easier to type. It is also said to help distinguish the generic category from the proprietary names which use the all-upper case version. Moreover, it is shorter and easier to type than the term Unix-like.
Unix-like is commonly used as a generic term referring to all operating systems that incorporate the major features of the early versions of UNIX, whether or not they officially call themselves UNIX or use the UNIX trademark. It is a broader term than Unix in the sense that the addition of the word -like eliminates any claim or implication that any system is UNIX (regardless of how UNIX might be defined, or spelled), and instead merely indicates that a system resembles the original UNIX systems. Thus, it is better at avoiding the controversial issues regarding what is, or can legally be called, UNIX, or Unix.
The Linux Information Project follows the convention of using the term UNIX to refer only to the original versions of the operating system that were developed at Bell Labs, to operating systems which use UNIX as part of their official names and to the UNIX trademark. It generally avoids the use of the word Unix by itself and instead uses Unix-like as a generic term to refer to all operating systems that resemble the original versions of UNIX as developed at Bell Labs, including those versions of UNIX and Linux.
Created May 22, 2005.