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Unix (; trademarked as UNIX) is a family of multitasking,
multiuser Multi-user software is computer software Software is a collection of Instruction (computer science), instructions that tell a computer how to work. This is in contrast to Computer hardware, hardware, from which the system is built and actually ...
computer
operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Examples of system software include operating systems like macOS macOS (; previously Mac OS X and later ...

operating system
s that derive from the original
AT&T AT&T Inc. is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, a s ...
Unix, whose development started in 1969 at the
Bell Labs Nokia Bell Labs (formerly named Bell Labs Innovations (1996–2007), AT&T Bell Laboratories (1984–1996) and Bell Telephone Laboratories (1925–1984)) is an American industrial research and scientific development company A company, abbrev ...
research center by
Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techni ...

Ken Thompson
,
Dennis Ritchie Dennis MacAlistair Ritchie (September 9, 1941 – October 12, 2011) was an American computer scientist A computer scientist is a person A person (plural people or persons) is a being that has certain capacities or attributes such as reaso ...

Dennis Ritchie
, and others. Initially intended for use inside the
Bell System The Bell System was the system of companies, led by the Bell Telephone Company The Bell Telephone Company, a common law joint stock company, was organized in Boston, Massachusetts on July 9, 1877, by Alexander Graham Bell's father-in-law Gar ...
, AT&T
license A license (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American English ...

license
d Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of California ...

University of California, Berkeley
(
BSD The Berkeley Software Distribution (BSD) is a discontinued based on , developed and distributed by the (CSRG) at the . The term "BSD" commonly refers to its descendants, including , , , and . BSD was initially called Berkeley Unix because it ...
),
Microsoft Microsoft Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinationa ...

Microsoft
(
Xenix Xenix is a discontinued version of the Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser Multi-user software is computer software Software is a collection of Instruction (computer science), instructions and data ...

Xenix
),
Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java (programming language), Java programming language, the Solaris ...
(
SunOS SunOS is a Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser Multi-user software is computer software Software is a collection of Instruction (computer science), instructions and data (computing), data that tell ...
/ Solaris), / HPE (
HP-UX HP-UX (from "Hewlett Packard Unix") is Hewlett Packard Enterprise The Hewlett Packard Enterprise Company (HPE) is an American multinational enterprise information technology company based in Houston, Texas Texas (, ) is a sta ...
), and
IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the C ...

IBM
(
AIX AIX (Advanced Interactive eXecutive, pronounced , “ay-eye-ex”), is a series of proprietary Unix operating systems developed and sold by IBM for several of its computer platforms. Originally released for the IBM RT PC RISC A reduc ...

AIX
). In the early 1990s, AT&T sold its rights in Unix to
Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah Provo is the third-largest city in Utah, United States. It is south of Salt Lake City along the Wasatch Front. Provo is the largest city and county se ...

Novell
, which then sold its Unix business to the
Santa Cruz Operation The Santa Cruz Operation, Inc. (usually known as SCO, pronounced either as individual letters or as a word) was an American software company, based in Santa Cruz, California, that was best known for selling three Unix operating system variants fo ...
(SCO) in 1995. The UNIX trademark passed to
The Open Group The Open Group is a global consortium that seeks to "enable the achievement of business objectives" by developing "Open-source model, open, vendor-neutral technology standards and certifications." It has over 840 member organizations and provides ...
, an industry consortium founded in 1996, which allows the use of the mark for certified operating systems that comply with the
Single UNIX Specification The Single UNIX Specification (SUS) is the collective name of a family of standards for computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can ...
(SUS). However, Novell continues to own the Unix copyrights, which the SCO Group, Inc. v. Novell, Inc. court case (2010) confirmed. Unix systems are characterized by a
modular design Modular design, or modularity in design, is a design principle that subdivides a system into smaller parts called ''modules'' (such as modular process skids), which can be independently created, modified, replaced, or exchanged with other modules or ...
that is sometimes called the "
Unix philosophy The Unix philosophy, originated by Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science Computer science deals with the theoretical foundations of information, algorithms and the architectu ...
". According to this philosophy, the operating system should provide a set of simple tools, each of which performs a limited, well-defined function. A unified and
inode The inode (index node) is a data structure in a Unix filesystem, Unix-style file system that describes a File system, file-system object such as a computer file, file or a directory (computing), directory. Each inode stores the attributes and disk ...
-based
filesystem In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwa ...
(the ) and an
inter-process communication In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Alg ...
mechanism known as "
pipes PIPES is the common name for piperazine-N,N′-bis(2-ethanesulfonic acid), and is a frequently used buffering agent in biochemistry. It is an ethanesulfonic acid buffer developed by Good et al. in the 1960s. Applications PIPES has two Acid dissoc ...
" serve as the main means of communication, and a
shell Shell may refer to: Architecture and design * Shell (structure)A shell is a type of structural element which is characterized by its geometry, being a three-dimensional solid whose thickness is very small when compared with other dimensions, and ...
scripting and command language (the
Unix shell A Unix shell is a command-line interpreter or shell Shell may refer to: Architecture and design * Shell (structure)A shell is a type of structural element which is characterized by its geometry, being a three-dimensional solid whose thickness i ...
) is used to combine the tools to perform complex workflows. Unix distinguishes itself from its predecessors as the first
portable Portable may refer to: General * Portable building, a manufactured structure that is built off site and moved in upon completion of site and utility work * Portable classroom, a temporary building installed on the grounds of a school to provide ad ...
operating system: almost the entire operating system is written in the
C programming language C (, as in the letter ''c'') is a general-purpose, procedural computer programming language A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/outp ...
, which allows Unix to operate on numerous platforms.


Overview

Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmers. The system grew larger as the operating system started spreading in academic circles, and as users added their own tools to the system and shared them with colleagues. At first, Unix was not designed to be
portable Portable may refer to: General * Portable building, a manufactured structure that is built off site and moved in upon completion of site and utility work * Portable classroom, a temporary building installed on the grounds of a school to provide ad ...
or for multi-tasking. Later, Unix gradually gained portability, multi-tasking and
multi-user Multi-user software is software, computer software that allows access by multiple User (computing), users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "mul ...
capabilities in a
time-sharing In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softw ...
configuration. Unix systems are characterized by various concepts: the use of
plain text In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softw ...

plain text
for storing data; a hierarchical
file system In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwa ...
; treating devices and certain types of
inter-process communication In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Alg ...
(IPC) as files; and the use of a large number of
software tools A programming tool or software development tool is a that s use to create, debug, maintain, or otherwise support other programs and applications. The term usually refers to relatively simple programs, that can be combined to accomplish a task, mu ...
, small programs that can be strung together through a
command-line interpreter A command-line interface (CLI) processes command (computing), commands to a computer program in the form of lines of text. The program which handles the interface is called a command-line interpreter or command-line processor. Operating systems ...
using
pipes PIPES is the common name for piperazine-N,N′-bis(2-ethanesulfonic acid), and is a frequently used buffering agent in biochemistry. It is an ethanesulfonic acid buffer developed by Good et al. in the 1960s. Applications PIPES has two Acid dissoc ...
, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are collectively known as the "
Unix philosophy The Unix philosophy, originated by Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science Computer science deals with the theoretical foundations of information, algorithms and the architectu ...
".
Brian Kernighan Brian Wilson Kernighan (; born 1942) is a Canadian computer scientist A computer scientist is a person A person (plural people or persons) is a being that has certain capacities or attributes such as reason, morality, consciousness or self- ...
and
Rob Pike Robert "Rob" C. Pike (born 1956) is a Canadian programmer A computer programmer, sometimes called a software developer, a programmer or more recently a coder (especially in more informal contexts), is a person who creates computer software ...
summarize this in ''
The Unix Programming Environment ''The Unix Programming Environment'', first published in 1984 by Prentice Hall Prentice Hall is an American major educational publisher owned by Savvas Learning Company. Prentice Hall publishes print and digital content for the 6–12 and hig ...
'' as "the idea that the power of a system comes more from the relationships among programs than from the programs themselves". By the early 1980s, users began seeing Unix as a potential universal operating system, suitable for computers of all sizes. The Unix environment and the client–server program model were essential elements in the development of the
Internet The Internet (or internet) is the global system of interconnected s that uses the (TCP/IP) to communicate between networks and devices. It is a ' that consists of private, public, academic, business, and government networks of local to ...

Internet
and the reshaping of computing as centered in
networks Network and networking may refer to: Arts, entertainment, and media * Network (1976 film), ''Network'' (1976 film), a 1976 American film * Network (2019 film), ''Network'' (2019 film), an Indian film * Network (album), ''Network'' (album), a 2004 ...
rather than in individual computers. Both Unix and the
C programming language C (, as in the letter ''c'') is a general-purpose, procedural computer programming language A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds of Input/outp ...
were developed by AT&T and distributed to government and academic institutions, which led to both being ported to a wider variety of machine families than any other operating system. The Unix operating system consists of many libraries and utilities along with the master control program, the
kernel Kernel may refer to: Computing * Kernel (operating system) In an operating system with a Abstraction layer, layered architecture, the kernel is the lowest level, has complete control of the hardware and is always in memory. In some systems it ...
. The kernel provides services to start and stop programs, handles the
file system In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwa ...
and other common "low-level" tasks that most programs share, and schedules access to avoid conflicts when programs try to access the same resource or device simultaneously. To mediate such access, the kernel has special rights, reflected in the distinction of ''kernel space'' from
user space A modern computer operating system usually segregates virtual memory into kernel space and user space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel s ...
, the latter being a priority realm where most application programs operate.


History

The origins of Unix date back to the mid-1960s when the
Massachusetts Institute of Technology Massachusetts Institute of Technology (MIT) is a in . Established in 1861, MIT has since played a key role in the development of modern technology and science, ranking it among the top in the world. Founded in response to the increasing ...
,
Bell Labs Nokia Bell Labs (formerly named Bell Labs Innovations (1996–2007), AT&T Bell Laboratories (1984–1996) and Bell Telephone Laboratories (1925–1984)) is an American industrial research and scientific development company A company, abbrev ...
, and
General Electric General Electric Company (GE) is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Mult ...
were developing
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level store, single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", C ...

Multics
, a
time-sharing In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softw ...
operating system for the GE-645 mainframe computer. Multics featured several innovations, but also presented severe problems. Frustrated by the size and complexity of Multics, but not by its goals, individual researchers at Bell Labs started withdrawing from the project. The last to leave were
Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techni ...

Ken Thompson
,
Dennis Ritchie Dennis MacAlistair Ritchie (September 9, 1941 – October 12, 2011) was an American computer scientist A computer scientist is a person A person (plural people or persons) is a being that has certain capacities or attributes such as reaso ...

Dennis Ritchie
,
Douglas McIlroy Malcolm Douglas McIlroy (born 1932) is a mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Greek: ) includes the study of such topics as numbers ( and ), formulas and related struct ...
, and
Joe Ossanna Joseph Frank Ossanna, Jr. (December 10, 1928 in Detroit (strait) , nicknames = The Motor City, Motown, Renaissance City, City of the Straits, The D, D-Town, Hockeytown, The Automotive Capital of the World, Rock City, The ...
, who decided to reimplement their experiences in a new project of smaller scale. This new operating system was initially without organizational backing, and also without a name. The new operating system was a single-tasking system. In 1970, the group coined the name ''Unics'' for ''Uniplexed Information and Computing Service'' as a
pun The pun, also known as paronomasia, is a form of word play Word play or wordplay (also: play-on-words) is a literary technique A narrative technique (known for literary fictional narratives as a literary technique, literary device, or fict ...
on ''Multics'', which stood for ''Multiplexed Information and Computer Services''.
Brian Kernighan Brian Wilson Kernighan (; born 1942) is a Canadian computer scientist A computer scientist is a person A person (plural people or persons) is a being that has certain capacities or attributes such as reason, morality, consciousness or self- ...
takes credit for the idea, but adds that "no one can remember" the origin of the final spelling ''Unix''. Dennis Ritchie, Doug McIlroy, and Peter G. Neumann also credit Kernighan. The operating system was originally written in
assembly language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, genera ...
, but in 1973, Version 4 Unix was rewritten in C. Version 4 Unix, however, still had many
PDP-11 The PDP-11 is a series of 16-bit 16-bit microcomputers are computers in which 16-bit microprocessors were the norm. A 16-bit register can store 216 different values. The range (computer programming), range of integer values that can be stored i ...
dependent codes, and was not suitable for porting. The first port to another platform was made five years later (1978) for the
Interdata 8/32 The Model 7/32 and Model 8/32 were 32-bit 32-bit microcomputers are computers in which 32-bit microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit ...
. In 1974, Ken Robinson of the Department of Computer Science at
University of New South Wales The University of New South Wales (UNSW), also known as UNSW Sydney, is a public In public relations and communication science, publics are groups of individual people, and the public (a.k.a. the general public) is the totality of such g ...
(UNSW) in
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
requested a copy of Unix for their PDP-11/40 minicomputer from Dennis Ritchie at Bell Labs. This 1975 installation made UNSW the first university outside the United States to run Unix. Bell Labs produced several versions of Unix that are collectively referred to as ''
Research Unix The term "Research Unix" refers to early versions of the Unix operating system for PDP-7, DEC PDP-7, PDP-11, VAX and Interdata 7/32 and 8/32 computers, developed in the Bell Labs Computing Sciences Research Center (CSRC). History The term ''Res ...
''. In 1975, the first source license for ''UNIX'' was sold to Donald B. Gillies at the
University of Illinois at Urbana–Champaign The University of Illinois Urbana-Champaign (U of I, Illinois, or colloquially the University of Illinois or UIUC) is a public In public relations and communication science, publics are groups of individual people, and the public (a.k.a. ...
Department of Computer Science (UIUC). UIUC graduate student Greg Chesson, who had worked on the Unix kernel at Bell Labs, was instrumental in negotiating the terms of the license. During the late 1970s and early 1980s, the influence of Unix in academic circles led to large-scale adoption of Unix (
BSD The Berkeley Software Distribution (BSD) is a discontinued based on , developed and distributed by the (CSRG) at the . The term "BSD" commonly refers to its descendants, including , , , and . BSD was initially called Berkeley Unix because it ...

BSD
and System V) by commercial startups, which in turn led to Unix fragmenting into multiple, similar but often slightly mutually-incompatible systems including
DYNIX DYNIX (''DYNamic UnIX'') was a Unix-like operating system developed by Sequent Computer Systems, based on 4.2BSDThe History of the Berkeley Software Distribution begins in the 1970s. 1BSD (PDP-11) The earliest distributions of Unix from Bell La ...
,
HP-UX HP-UX (from "Hewlett Packard Unix") is Hewlett Packard Enterprise The Hewlett Packard Enterprise Company (HPE) is an American multinational enterprise information technology company based in Houston, Texas Texas (, ) is a sta ...
,
SunOS SunOS is a Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser Multi-user software is computer software Software is a collection of Instruction (computer science), instructions and data (computing), data that tell ...
/ Solaris,
AIX AIX (Advanced Interactive eXecutive, pronounced , “ay-eye-ex”) is a series of Proprietary software, proprietary Unix operating systems developed and sold by IBM for several of its computer platforms. Originally released for the IBM RT P ...
, and
Xenix Xenix is a discontinued version of the Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser Multi-user software is computer software Software is a collection of Instruction (computer science), instructions and data ...

Xenix
. In the late 1980s, AT&T
Unix System Laboratories Unix System Laboratories (USL), sometimes written UNIX System Laboratories to follow relevant trademark guidelines of the time, was an American software laboratory and product development company that existed from 1989 through 1993. At first wh ...
and
Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java (programming language), Java programming language, the Solaris ...
developed System V Release 4 (
SVR4 Unix System V (pronounced: "System Five") is one of the first commercial versions of the Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser Multi-user software is computer software Software is a collection of In ...
), which was subsequently adopted by many commercial Unix vendors. In the 1990s, Unix and
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Examples of system software include operating s ...
systems grew in popularity and became the operating system of choice for over 90% of the world's top 500 fastest supercomputers, as BSD and
Linux Linux ( or ) is a family of open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product ...

Linux
distributions were developed through collaboration by a worldwide network of programmers. In 2000, Apple released
Darwin Darwin most often refers to: * Charles Darwin (1809–1882), English naturalist and writer, best known as the originator of the theory of biological evolution by natural selection * Darwin, Northern Territory, a capital city in Australia * Darwin ( ...
, also a Unix system, which became the core of the Mac OS X operating system, later renamed
macOS macOS (; previously Mac OS X and later OS X) is a proprietary {{Short pages monitor (complementary film to the preceding "Making Computers More Productive")
audio bsdtalk170 - Marshall Kirk McKusick at DCBSDCon -- on history of tcp/ip (in BSD) -- abridgement of the three lectures on the history of BSD.



BYTE Magazine, September 1986: UNIX and the MC68000
a software perspective on the MC68000 CPU architecture and UNIX compatibility {{Authority control Unix, 1969 software Operating system families Time-sharing operating systems