Unix is an operating system designed by Bell Labs to handle time sharing on their DEC mainframe computers. After abandoning the Multics OS project, Bell was in need of an operating system to power it's DEC mainframes. A notable Bell Multics developer designed the Unix code base from scratch specifically for the DEC PDP-7 machines. Four years later, the OS was completely rewritten in the C programming language. At the time, Unix excelled as a multitasking, multiuser OS that ran on a wide variety of hardware: the only system of it's kind. Bell parent AT&T licensed the code for outside use, spurring a swift development period in which four major versions were released in just over two years. Since then, Unix has inspired many clones and versions. Now owned by the Open Group, the Unix trademark is used as a certification measure for independent operating systems that meet the Single UNIX Specification. Other similar systems, such as Linux and Mac OS-X, are termed Unix-like.
In the late 1970's AT&T attempted to consolidate the differing licenses under which Unix was distributed under one general license that encompassed government, corporate, and university applications. This turned out to be unfavorable to the universities, who had enjoyed almost complete freedom to do as they pleased with the code. In response to the new license terms, the University of California at Berkeley released it's BSD operating system, developed from the Unix code base under the original terms of the license. This was the first of dozens of Unix clones, including Solaris, AIX, and Microsoft's own Xenix. These systems were used almost exclusively on large networking machines and workstations. Later clones such as Linux and Mac OS-X helped Unix-type systems gain widespread desktop adaptation. Today, with the exception of the Microsoft Windows family of operating systems, all operating systems in widespread use are based upon the Unix model.
The name Unix was chosen as a shortened form of Unics, itself a play on the name Multics. The first official use of the name was spelled UNIX, as terminals capable of supporting lower-case letters were fairly new at the time and the main developer rebelled the change. Arguing that UNIX is not an acronym, the same developer had lobbied to have the official spelling changed to Unix, unsuccessfully. The US patent on the trademark today remains UNIX and the official open standard, the Single UNIX Specification, uses only the all-caps version of the name. The Open Group does, however, recommend that all non-UNIX systems be referred to as Unix-like systems, with only the first letter capitalized.
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