Operating Systems; Computer Science; Information Technology


UNIX is a computer operating system originally developed by researchers at Bell Laboratories in 1969. The term is also used to refer to later operating systems based in part on its source code. Several of the original UNIX operating system's features, such as its hierarchical file system and multiuser support, became standard in later systems.


The creators of UNIX were Dennis Ritchie (standing) and Ken Thompson (sitting).

The creators of UNIX were Dennis Ritchie (standing) and Ken Thompson (sitting).

As computer technology rapidly developed in the mid-twentieth century, programmers sought to create means of interfacing with computers and making use of their functions in a more straightforward, intuitive way. Chief among the goals of many programmers was the creation of an operating system (OS). OSs are specialized programs that manage all of computers’ processes and functions. Although many different OSs were created over the decades, UNIX proved to be one of the most influential. UNIX inspired numerous later OSs and continues to be used in various forms into the twenty-first century.

Development of the original UNIX OS began in 1969 at Bell Laboratories, a research facility then owned by AT&T. Researchers at Bell had been working on the Multiplexed Information and Computing Service (Multics) project in collaboration with the Massachusetts Institute of Technology and General Electric. The group had focused on creating systems that allowed multiple users to access a computer at once. After AT&T left the project, Bell programmers Ken Thompson and Dennis Ritchie began work on an OS. Thompson coded the bulk of the system, which consisted of 4,200 lines of code, in the summer of 1969, running it on an outdated PDP-7 computer.

The OS was initially named the Unmultiplexed Information and Computing Service, a play on the name of the Multics project. That name was later shortened to UNIX. Thompson, Ritchie, and their colleagues continued to work on UNIX over the next several years. In 1973 they rewrote the OS in the new programming language C, created by Ritchie. UNIX gained popularity outside of Bell Laboratories in the mid-1970s. It subsequently inspired the creation of many UNIX variants and UNIX-like OSs.


In keeping with its origins as a project carried out by former Multics researchers, UNIX was designed to have multiuser capabilities. This enabled multiple people to use a single computer running UNIX at the same time. This was an especially important feature in the late 1960s and early 1970s. At this time, computers were not personal computers but large, expensive mainframes that took up a significant amount of space and power. Multiuser capabilities made it possible for the organization using the UNIX OS to maximize the functions of their computers.

UNIX is also a multitasking system, meaning it can carry out multiple operations at once. One of the first programs designed for UNIX was a text-editing program needed by the employees of Bell Laboratories. Over time, programmers wrote numerous programs compatible with the OS and its later variants, including games, web browsers, and design software.


At the time that UNIX was first developed, AT&T was prohibited from selling products in fields other than telecommunications. The company was therefore unable to sell its researchers’ creation. Instead, the company licensed UNIX's source code to various institutions. Programmers at those many institutions rewrote portions of the OS's code, creating UNIX variants that suited their needs. Perhaps the most influential new form of UNIX was the Berkeley Software Distribution variant, developed at the University of California, Berkeley, in the late 1970s.

In the early twenty-first century, the multitude of UNIX variants and UNIX-derived OSs are divided into two main categories. Those that conform to standards established by an organization known as the Open Group, which holds the trademark to the UNIX name, may be referred to as “certified UNIX operating systems.” Systems that are similar to UNIX but do not adhere to the Open Group's standards are typically known as “UNIX-like operating systems.” The latter category includes Apple's OS X and the free, open-source system Linux. The mobile OSs Android and Apple iOS also fall under this category and account for hundreds of millions of users, arguably making UNIX-derived OSs the most widely used systems ever.

—Joy Crelin

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