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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 and data (computing), data that tell a computer how to work. This is in contrast to Computer hardware, physical hardware, from wh ...
computer
operating system An operating system (OS) is system software that manages computer hardware, computer software, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), sch ...

operating system
s that derive from the original
AT&T AT&T Inc. is an American multinational conglomerate holding company, Delaware-registered but it is headquartered at Whitacre Tower in Downtown Dallas, Texas.Godinez, Victor and David McLemore.AT&T moving headquarters to Dallas from San An ...
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. He created the C programming language and, with long-time colleague Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an Ame ...
, and others. Initially intended for use inside the
Bell System The Bell System was the system of companies, led by the Bell Telephone Company and later by AT&T AT&T Inc. is an American multinational conglomerate holding company, Delaware-registered but it is headquartered at Whitacre Tower in ...
, 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 operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley. The term "BSD" commonly re ...
),
Microsoft Microsoft Corporation is an American multinational corporation, multinational technology company with headquarters in Redmond, Washington. It develops, manufactures, licenses, supports, and sells Software, computer software, consumer electroni ...

Microsoft
(
Xenix Xenix is a discontinued version of the Unix operating system for various microcomputer platforms, licensed by Microsoft from AT&T Corporation in the late 1970s. The Santa Cruz Operation (SCO) later acquired exclusive rights to the software, and ev ...

Xenix
),
Sun Microsystems Sun Microsystems, Inc. (Sun for short) is a defunct American company that sold computers, computer components, software, and information technology services and created the Java (programming language), Java programming language, the Solaris oper ...
(
SunOS SunOS is a Unix Unix (; trademarked as UNIX) is a family of Computer multitasking, multitasking, multiuser computer operating systems that derive from the original AT&T Corporation, AT&T Unix, whose development started in the 1970s at the Bel ...
/ 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 ...
). 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. Its most significant product was the multi-System platform, platform network operating system known as Novell NetWare. Under the leadership of chief executi ...

Novell
, which then sold its Unix business to the
Santa Cruz Operation Santa Cruz Operation (SCO) was a software company based in Santa Cruz, California which was best known for selling three Unix variants for Intel x86 processors: Xenix, SCO UNIX (later known as SCO OpenServer), and UnixWare. Eric S. Raymond, Eric ...
(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 i ...
scripting and command language (the
Unix shell A Unix shell is a command-line interpreter or shell that provides a command line user interface 300px, The Reactable, an example of a tangible user interface ">tangible_user_interface.html" ;"title="Reactable, an example of a tangible user int ...
) 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 ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing ...
, 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 computer software Software is a collection of Instruction (computer science), instructions and data (computing), data that tell a computer how to work. This is in contrast to Computer hardware, physical hardware, from wh ...
capabilities in a
time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and computer multitasking, multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Numb ...
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, a file system or filesystem (often abbreviated to fs) controls how data is Computer data storage, stored and retrieved. Without a file system, data placed in a storage medium would be one large body of data with no way to tell where ...
; 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 computer program A computer program is a collection of instructions that can be executed by a computer to perform a specific task. A computer program is usually written by a computer progr ...
, small programs that can be strung together through a
command-line interpreter A command-line interface (CLI) processes 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 implement a command- ...
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. He worked at Bell Labs and contributed to the development of Unix alongside Unix creators Ken Thompson and Dennis Ritchie. Kernighan's name became widely known through co ...
and
Rob Pike Robert "Rob" C. Pike (born 1956) is a Canadian programmer and author An author is the creator or originator of any written work such as a book or play, and is also considered a writer. More broadly defined, an author is "the person who origina ...
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 (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''network of networks'' t ...

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 ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing ...
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) The kernel is a computer program at the core of a computer's operating system that has complete control over everything in the system. It is the "portion of the operating system co ...
. The kernel provides services to start and stop programs, handles the
file system In computing, a file system or filesystem (often abbreviated to fs) controls how data is Computer data storage, stored and retrieved. Without a file system, data placed in a storage medium would be one large body of data with no way to tell where ...
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 An operating system (OS) is system software that manages computer hardware, computer software, software resources, and provides common daemon (computing), services for computer programs. Time-sharing opera ...
, 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 private land-grant research university in Cambridge, Massachusetts Cambridge ( ) is a city in Middlesex County, Massachusetts, Middlesex County, Massachusetts, and part of the Greater Bos ...
,
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 corporation, multinational Conglomerate (company), conglomerate incorporated in New York State and headquartered in Boston. Until 2021, the company operated through GE Aviation, aviati ...
were developing
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and computer multitas ...

Multics
, a
time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and computer multitasking, multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Numb ...
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. He created the C programming language and, with long-time colleague Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an Ame ...
,
Douglas McIlroy Malcolm Douglas McIlroy (born 1932) is a mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathem ...
, 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 that exploits multiple meanings of a term, or of similar-sounding words, for an intended humorous or rhetoric Rhetoric () is the Art (skill), art of persuasion, which alon ...
on ''Multics'', which stood for ''Multiplexed Information and Computer Services''.
Brian Kernighan Brian Wilson Kernighan (; born 1942) is a Canadian computer scientist. He worked at Bell Labs and contributed to the development of Unix alongside Unix creators Ken Thompson and Dennis Ritchie. Kernighan's name became widely known through co ...
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, assembly language (or assembler language), often abbreviated asm, is any low-level programming language in which there is a very strong correspondence between the instructions in the language and the computer architecture ...
, 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 (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, smal ...

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 UnixResearch Unix refers to early versions of the Unix operating system for 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 ''Research Unix'' ...
''. 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 ...
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 operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley. The term "BSD" commonly re ...

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 Berkeley Software Distribution#4.2BSD, 4.2BSD and modified to run on Intel-based symmetric multiprocessing, symmetric multiprocessor hardwar ...
,
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 Computer multitasking, multitasking, multiuser computer operating systems that derive from the original AT&T Corporation, AT&T Unix, whose development started in the 1970s at the Bel ...
/ Solaris,
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 ...
, and
Xenix Xenix is a discontinued version of the Unix operating system for various microcomputer platforms, licensed by Microsoft from AT&T Corporation in the late 1970s. The Santa Cruz Operation (SCO) later acquired exclusive rights to the software, and ev ...

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 whol ...
and
Sun Microsystems Sun Microsystems, Inc. (Sun for short) is a defunct American company that sold computers, computer components, software, and information technology services and created the Java (programming language), Java programming language, the Solaris oper ...
developed System V Release 4 (
SVR4 Unix System V (pronounced: "System Five") is one of the first commercial versions of the Unix operating system An operating system (OS) is system software that manages computer hardware, computer software, software resources, and provides c ...
), 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 is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like Ap ...
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 free and open-source software, open-source Unix-like operating systems based on the Linux kernel, an Kernel (computing), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is t ...

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 software, proprietary graphical user interface, graphical operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for A ...
. Unix operating systems are widely used in modern servers,
workstation A workstation is a special computer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network A local area network (LAN) is a computer net ...

workstation
s, and
mobile device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known a ...
s.


Standards

In the late 1980s, an open operating system standardization effort now known as
POSIX The Portable Operating System Interface (POSIX) is a family of standardization, standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines the application programming interface (API), a ...
provided a common baseline for all operating systems;
IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a professional association A professional association (also called a professional body, professional organization, or professional society) seeks to advocacy, further a particul ...
based POSIX around the common structure of the major competing variants of the Unix system, publishing the first POSIX standard in 1988. In the early 1990s, a separate but very similar effort was started by an industry consortium, the
Common Open Software Environment The Common Open Software Environment (COSE) was an initiative formed in March 1993 by the major Unix Unix (; trademarked as UNIX) is a family of Computer multitasking, multitasking, multiuser computer operating systems that derive from the or ...
(COSE) initiative, which eventually became 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) administered by
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 ...
. Starting in 1998, the Open Group and IEEE started the
Austin Group The Austin Group or the Austin Common Standards Revision Group is a joint technical working groupWorking Group may refer to: * Working group, an interdisciplinary group of researchers; or * Working Group (dogs), kennel club designation for certain ...
, to provide a common definition of POSIX and the Single UNIX Specification, which, by 2008, had become the Open Group Base Specification. In 1999, in an effort towards compatibility, several Unix system vendors agreed on SVR4's
Executable and Linkable Format 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 soft ...
(ELF) as the standard for binary and object code files. The common format allows substantial binary compatibility among different Unix systems operating on the same CPU architecture. The
Filesystem Hierarchy Standard The Filesystem Hierarchy Standard (FHS) defines the directory structure In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic p ...

Filesystem Hierarchy Standard
was created to provide a reference directory layout for Unix-like operating systems; it has mainly been used in Linux.


Components

The Unix system is composed of several components that were originally packaged together. By including the development environment, libraries, documents and the portable, modifiable source code for all of these components, in addition to the
kernel Kernel may refer to: Computing * Kernel (operating system) The kernel is a computer program at the core of a computer's operating system that has complete control over everything in the system. It is the "portion of the operating system co ...
of an operating system, Unix was a self-contained software system. This was one of the key reasons it emerged as an important teaching and learning tool and has had such a broad influence. The inclusion of these components did not make the system large the original V7 UNIX distribution, consisting of copies of all of the compiled binaries plus all of the source code and documentation occupied less than 10 MB and arrived on a single nine-track
magnetic tape Magnetic tape is a medium for magnetic recording, made of a thin, magnetizable coating on a long, narrow strip of plastic film Plastic film is a thin continuous polymeric material. Thicker plastic material is often called a "sheet". Thes ...
. The printed documentation, typeset from the online sources, was contained in two volumes. The names and filesystem locations of the Unix components have changed substantially across the history of the system. Nonetheless, the V7 implementation is considered by many to have the canonical early structure: * ''Kernel'' source code in /usr/sys, composed of several sub-components: ** ''conf'' configuration and machine-dependent parts, including boot code ** ''dev'' device drivers for control of hardware (and some pseudo-hardware) ** ''sys'' operating system "kernel", handling memory management, process scheduling, system calls, etc. ** ''h'' header files, defining key structures within the system and important system-specific invariables * ''Development environment'' early versions of Unix contained a development environment sufficient to recreate the entire system from source code: ** '' ed'' text editor, for creating source code files ** ''cc''
C 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 ...
compiler (first appeared in V3 Unix) ** ''as'' machine-language assembler for the machine ** ''ld'' linker, for combining object files ** ''lib'' object-code libraries (installed in /lib or /usr/lib). ''
libc The C standard library or libc is the standard library A standard library in computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perf ...
'', the system library with C run-time support, was the primary library, but there have always been additional libraries for things such as mathematical functions (''
libm C mathematical operations are a group of functions in the standard library of the C programming language implementing basic mathematical functions. All functions use floating-point numbers in one manner or another. Different C standards provide ...
'') or database access. V7 Unix introduced the first version of the modern "Standard I/O" library ''stdio'' as part of the system library. Later implementations increased the number of libraries significantly. ** ''
make Make or MAKE may refer to: *Make (magazine), ''Make:'' (magazine), an American magazine and television program *Make (software), a computer-assisted software engineering tool *Make, Botswana, a small village in the Kalahari Desert *Make Architects, ...
'' build manager (introduced in
PWB/UNIX The Programmer's Workbench (PWB/UNIX) is an early, now discontinued, version of the Unix operating system that had been created in the Bell Labs Computer Science Research Group of AT&T Corporation, AT&T. Its stated goal was to provide a time-shari ...
), for effectively automating the build process ** ''include'' header files for software development, defining standard interfaces and system invariants ** ''Other languages'' V7 Unix contained a Fortran-77 compiler, a programmable arbitrary-precision calculator (''bc'', ''dc''), and the
awk AWK (''awk'') is a domain-specific languageA domain-specific language (DSL) is a computer languageA computer language is a method of communication with a computer A computer is a machine that can be programmed to carry out sequences of ari ...
scripting language; later versions and implementations contain many other language compilers and toolsets. Early BSD releases included
Pascal Pascal, Pascal's or PASCAL may refer to: People and fictional characters * Pascal (given name), including a list of people with the name * Pascal (surname), including a list of people and fictional characters with the name ** Blaise Pascal, French ...
tools, and many modern Unix systems also include the
GNU Compiler Collection The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, Computer architecture, hardware architectures and operating systems. The Free Software Foundation (FSF) distribut ...
as well as or instead of a proprietary compiler system. ** ''Other tools'' including an object-code archive manager ('' ar''), symbol-table lister (''nm''), compiler-development tools (e.g. '' lex'' & ''
yacc Yacc (Yet Another Compiler-Compiler) is a computer program A computer program is a collection of instructions that can be executed by a computer to perform a specific task. A computer program is usually written by a computer programmer in a ...
''), and debugging tools. * ''Commands'' Unix makes little distinction between commands (user-level programs) for system operation and maintenance (e.g. ''
cron The software utility cron also known as cron job is a time-based job scheduler in Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, while not necessarily ...
''), commands of general utility (e.g. ''
grep grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed (text editor), ed command ''g/re/p'' (''globally search for a regular expression and print matching lines''), ...

grep
''), and more general-purpose applications such as the text formatting and typesetting package. Nonetheless, some major categories are: ** '' sh'' the "shell" programmable
command-line interpreter A command-line interface (CLI) processes 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 implement a command- ...
, the primary user interface on Unix before window systems appeared, and even afterward (within a "command window"). ** ''Utilities'' the core toolkit of the Unix command set, including '' cp'', '''', ''
grep grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed (text editor), ed command ''g/re/p'' (''globally search for a regular expression and print matching lines''), ...

grep
'', '' find'' and many others. Subcategories include: *** ''System utilities'' administrative tools such as '' mkfs'', ''
fsck The system utility fsck (''file system consistency check'') is a tool for checking the consistency of a file system In computing, a file system or filesystem (often abbreviated to fs) controls how data is Computer data storage, stored and retrie ...
'', and many others. *** ''User utilities'' environment management tools such as ''passwd'', ''kill'', and others. ** ''Document formatting'' Unix systems were used from the outset for document preparation and typesetting systems, and included many related programs such as ''
nroff nroff (short for "new roff") is a text-formatting computer program, program on Unix and Unix-like operating systems. It produces output suitable for simple fixed-width computer printer, printers and computer terminal, terminal windows. It is an i ...
'', ''
troff troff (), short for "typesetter roff", is the major component of a document processing system developed by AT&T Corporation AT&T Corporation, originally the American Telephone and Telegraph Company, is the subsidiary of AT&T Inc. that prov ...
'', '''', '' eqn'', '' refer'', and '' pic''. Some modern Unix systems also include packages such as
TeX TeX (, see below), stylized within the system as TeX, is a typesetting system which was designed and mostly written by Donald Knuth and released in 1978. TeX is a popular means of typesetting complex mathematical formulae; it has been noted ...
and
Ghostscript Ghostscript is a suite of software based on an interpreter for Adobe Systems Adobe Inc. ( ) is an American multinational computer software Software is a collection of Instruction (computer science), instructions and data (computing), dat ...

Ghostscript
. ** ''Graphics'' the ''plot'' subsystem provided facilities for producing simple vector plots in a device-independent format, with device-specific interpreters to display such files. Modern Unix systems also generally include
X11 The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting with ...

X11
as a standard windowing system and
GUI#REDIRECT graphical user interface The graphical user interface (GUI "UI" by itself is still usually pronounced . or ) is a form of user interface that allows User (computing), users to Human–computer interaction, interact with electronic devic ...

GUI
, and many support
OpenGL OpenGL (Open Graphics Library) is a cross-language, cross-platform application programming interface (API) for rendering 2D computer graphics, 2D and 3D computer graphics, 3D vector graphics. The API is typically used to interact with a graphic ...
. ** ''Communications'' early Unix systems contained no inter-system communication, but did include the inter-user communication programs ''mail'' and ''write''. V7 introduced the early inter-system communication system
UUCP UUCP is an acronym An acronym is a word or name formed from the initial components of a longer name or phrase, usually using individual initial letters, as in NATO (North Atlantic Treaty Organization) or European Union, EU (European Union), bu ...
, and systems beginning with BSD release 4.1c included
TCP/IP The Internet protocol suite is the conceptual model A conceptual model is a representation of a system, made of the composition of concept Concepts are defined as abstract ideas or general notions that occur in the mind, in speech, or in tho ...
utilities. * ''Documentation'' Unix was the first operating system to include all of its documentation online in machine-readable form. The documentation included: ** ''
man A man is an adult male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot sexual reproduction, reproduce ...
'' manual pages for each command, library component,
system call 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 soft ...
, header file, etc. ** ''doc'' longer documents detailing major subsystems, such as the C language and troff


Impact

The Unix system had a significant impact on other operating systems. It achieved its reputation by its interactivity, by providing the software at a nominal fee for educational use, by running on inexpensive hardware, and by being easy to adapt and move to different machines. Unix was originally written in
assembly language In computer programming, assembly language (or assembler language), often abbreviated asm, is any low-level programming language in which there is a very strong correspondence between the instructions in the language and the computer architecture ...
, but was soon rewritten in C, a
high-level programming language 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 Algori ...
. Although this followed the lead of
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and computer multitas ...

Multics
and
Burroughs MCP The MCP (Master Control Program) is the proprietary operating system An operating system (OS) is system software that manages computer hardware, computer software, software resources, and provides common daemon (computing), services for comput ...
, it was Unix that popularized the idea. Unix had a drastically simplified file model compared to many contemporary operating systems: treating all kinds of files as simple byte arrays. The file system hierarchy contained machine services and devices (such as printers, terminals, or
disk drive Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is ...
s), providing a uniform interface, but at the expense of occasionally requiring additional mechanisms such as
ioctl 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 mode flags to access features of the hardware that did not fit the simple "stream of bytes" model. The Plan 9 operating system pushed this model even further and eliminated the need for additional mechanisms. Unix also popularized the hierarchical file system with arbitrarily nested subdirectories, originally introduced by Multics. Other common operating systems of the era had ways to divide a storage device into multiple directories or sections, but they had a fixed number of levels, often only one level. Several major proprietary operating systems eventually added recursive subdirectory capabilities also patterned after Multics. DEC's
RSX-11M RSX-11 is a discontinued family of multi-user real-time operating systems for PDP-11 computers created by Digital Equipment Corporation. In widespread use through the late 1970s and early 1980s, RSX-11 was influential in the development of later op ...
's "group, user" hierarchy evolved into
OpenVMS OpenVMS, often referred to as just VMS, is a multi-user Multi-user software is computer software Software is a collection of Instruction (computer science), instructions and data (computing), data that tell a computer how to work. This is in ...
directories,
CP/M CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/Intel 8085, 85-based microcomputers by Gary Kildall of Digital Research, Inc. ...
's volumes evolved into
MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and few operatin ...
2.0+ subdirectories, and HP's MPE group.account hierarchy and IBM's SSP and
OS/400 IBM i (the ''i'' standing for ''integrated'') is an operating system An operating system (OS) is system software that manages computer hardware, computer software, software resources, and provides common daemon (computing), services for compute ...
library systems were folded into broader POSIX file systems. Making the command interpreter an ordinary user-level program, with additional commands provided as separate programs, was another Multics innovation popularized by Unix. The
Unix shell A Unix shell is a command-line interpreter or shell that provides a command line user interface 300px, The Reactable, an example of a tangible user interface ">tangible_user_interface.html" ;"title="Reactable, an example of a tangible user int ...
used the same language for interactive commands as for scripting (
shell script A shell script is a computer program designed to be run by the Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be scripting languages. Typical operations performed by shell scripts include file mani ...
s – there was no separate job control language like IBM's Job Control Language, JCL). Since the shell and OS commands were "just another program", the user could choose (or even write) their own shell. New commands could be added without changing the shell itself. Unix's innovative command-line syntax for creating modular chains of producer-consumer processes (pipeline (Unix), pipelines) made a powerful programming paradigm (coroutines) widely available. Many later command-line interpreters have been inspired by the Unix shell. A fundamental simplifying assumption of Unix was its focus on newline-Delimiter, delimited text for nearly all file formats. There were no "binary" editors in the original version of Unix – the entire system was configured using textual shell command scripts. The common denominator in the I/O system was the byte – unlike Record-oriented filesystem, "record-based" file systems. The focus on text for representing nearly everything made Unix pipes especially useful and encouraged the development of simple, general tools that could be easily combined to perform more complicated ''ad hoc'' tasks. The focus on text and bytes made the system far more scalable and portable than other systems. Over time, text-based applications have also proven popular in application areas, such as printing languages (PostScript, ODF), and at the application layer of the Internet Protocol Suite, Internet protocols, e.g., File Transfer Protocol, FTP, Simple Mail Transfer Protocol, SMTP, Hypertext Transfer Protocol, HTTP, SOAP, and Session Initiation Protocol, SIP. Unix popularized a syntax for regular expressions that found widespread use. The Unix programming interface became the basis for a widely implemented operating system interface standard (POSIX, see above). The
C programming language ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing ...
soon spread beyond Unix, and is now ubiquitous in systems and applications programming. Early Unix developers were important in bringing the concepts of Modularity (programming), modularity and reusability into software engineering practice, spawning a "software tools" movement. Over time, the leading developers of Unix (and programs that ran on it) established a set of cultural norms for developing software, norms which became as important and influential as the technology of Unix itself; this has been termed 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 ...
. The Internet protocol suite, TCP/IP networking protocols were quickly implemented on the Unix versions widely used on relatively inexpensive computers, which contributed to the
Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''network of networks'' t ...

Internet
explosion of worldwide real-time connectivity, and which formed the basis for implementations on many other platforms. The Unix policy of extensive on-line documentation and (for many years) ready access to all system source code raised programmer expectations, and contributed to the launch of the free software movement in 1983.


Free Unix and Unix-like variants

In 1983, Richard Stallman announced the GNU (short for "GNU's Not Unix") project, an ambitious effort to create a free software
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like Ap ...
system; "free" in the sense that everyone who received a copy would be free to use, study, modify, and redistribute it. The GNU project's own kernel development project, GNU Hurd, had not yet produced a working kernel, but in 1991 Linus Torvalds released the Linux kernel as free software under the GNU General Public License. In addition to their use in the GNU operating system, many GNU packages – such as the
GNU Compiler Collection The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, Computer architecture, hardware architectures and operating systems. The Free Software Foundation (FSF) distribut ...
(and the rest of the GNU toolchain), the glibc, GNU C library and the Coreutils, GNU core utilities – have gone on to play central roles in other free Unix systems as well. Linux distributions, consisting of the Linux kernel and large collections of compatible software have become popular both with individual users and in business. Popular distributions include Red Hat Enterprise Linux, Fedora (operating system), Fedora, SUSE Linux, SUSE Linux Enterprise, openSUSE, Debian, Ubuntu, Linux Mint, Mandriva Linux, Slackware Linux, Arch Linux and Gentoo Linux, Gentoo. A free derivative of
BSD The Berkeley Software Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley. The term "BSD" commonly re ...

BSD
Unix, 386BSD, was released in 1992 and led to the NetBSD and FreeBSD projects. With the 1994 settlement of a lawsuit brought against the University of California and Berkeley Software Design Inc. (''USL v. BSDi'') by
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 whol ...
, it was clarified that Berkeley had the right to distribute BSD Unix for free if it so desired. Since then, BSD Unix has been developed in several different product branches, including OpenBSD and DragonFly BSD. Linux and BSD are increasingly filling the market needs traditionally served by proprietary Unix operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. Because of the modular design of the Unix model, sharing components is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and some systems also include GNU utilities in their distributions. In a 1999 interview, Dennis Ritchie voiced his opinion that Linux and BSD operating systems are a continuation of the basis of the Unix design, and are derivatives of Unix: In the same interview, he states that he views both Unix and Linux as "the continuation of ideas that were started by Ken and me and many others, many years ago". OpenSolaris was the free software counterpart to Solaris developed by
Sun Microsystems Sun Microsystems, Inc. (Sun for short) is a defunct American company that sold computers, computer components, software, and information technology services and created the Java (programming language), Java programming language, the Solaris oper ...
, which included a CDDL-licensed kernel and a primarily GNU userland. However, Oracle Corporation, Oracle discontinued the project upon their acquisition of Sun, which prompted a group of former Sun employees and members of the OpenSolaris community to fork OpenSolaris into the illumos kernel. As of 2014, illumos remains the only active open-source System V derivative.


ARPANET

In May 1975, RFC 681 described the development of ''Network Unix'' by the Center for Advanced Computation at the University of Illinois Urbana-Champaign. The Unix system was said to "present several interesting capabilities as an ARPANET mini-host". At the time, Unix required a license from Bell Labs, Bell Telephone Laboratories that cost US$20,000 for non-university institutions, while universities could obtain a license for a nominal fee of $150. It was noted that Bell was "open to suggestions" for an ARPANET-wide license. The RFC specifically mentions that Unix "offers powerful local processing facilities in terms of user programs, several Compiler, compilers, an Text editor, editor based on QED (text editor), QED, a versatile document preparation system, and an efficient
file system In computing, a file system or filesystem (often abbreviated to fs) controls how data is Computer data storage, stored and retrieved. Without a file system, data placed in a storage medium would be one large body of data with no way to tell where ...
featuring sophisticated access control, Mount (computing), mountable and de-mountable volumes, and a unified treatment of peripherals as Device file, special files." The latter permitted the Network Control Program (NCP) to be integrated within the Unix file system, treating Transport layer, network connections as special files that could be accessed through standard Unix System call, I/O calls, which included the added benefit of closing all connections on program exit, should the user neglect to do so. The modular design of Unix allowed them "to minimize the amount of code added to the basic Unix
kernel Kernel may refer to: Computing * Kernel (operating system) The kernel is a computer program at the core of a computer's operating system that has complete control over everything in the system. It is the "portion of the operating system co ...
", with much of the NCP code in a Memory paging, swappable user process, running only when needed.


Branding

In October 1993,
Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah. Its most significant product was the multi-System platform, platform network operating system known as Novell NetWare. Under the leadership of chief executi ...

Novell
, the company that owned the rights to the Unix System V source at the time, transferred the trademarks of Unix to the X/Open Company (now
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 ...
), and in 1995 sold the related business operations to
Santa Cruz Operation Santa Cruz Operation (SCO) was a software company based in Santa Cruz, California which was best known for selling three Unix variants for Intel x86 processors: Xenix, SCO UNIX (later known as SCO OpenServer), and UnixWare. Eric S. Raymond, Eric ...
(SCO). Whether Novell also sold the copyrights to the actual software was the subject of a federal lawsuit in 2006, ''SCO v. Novell'', which Novell won. The case was appealed, but on August 30, 2011, the United States Court of Appeals for the Tenth Circuit affirmed the trial decisions, closing the case. Unix vendor SCO Group, SCO Group Inc. accused Novell of slander of title. The present owner of the trademark ''UNIX'' is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to 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 ...
qualify as "UNIX" (others are called "
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like Ap ...
"). By decree of The Open Group, the term "UNIX" refers more to a class of operating systems than to a specific implementation of an operating system; those operating systems which meet The Open Group's Single UNIX Specification should be able to bear the UNIX 98 or UNIX 03 trademarks today, after the operating system's vendor pays a substantial certification fee and annual trademark royalties to The Open Group. Systems that have been licensed to use the UNIX trademark include
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 ...
, EulerOS,
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 ...
, Inspur K-UX, IRIX,
macOS macOS (; previously Mac OS X and later OS X) is a Proprietary software, proprietary graphical user interface, graphical operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for A ...
, Solaris, Tru64 UNIX (formerly "Digital UNIX", or OSF/1), and z/OS. Notably, EulerOS and Inspur K-UX are Linux distributions certified as UNIX 03 compliant. Sometimes a representation like ''Un*x'', ''*NIX'', or ''*N?X'' is used to indicate all operating systems similar to Unix. This comes from the use of the asterisk (''*'') and the question mark characters as wildcard indicators in many utilities. This notation is also used to describe other Unix-like systems that have not met the requirements for UNIX branding from the Open Group. The Open Group requests that ''UNIX'' is always used as an adjective followed by a generic term such as ''system'' to help avoid the creation of a genericized trademark. ''Unix'' was the original formatting, but the usage of ''UNIX'' remains widespread because it was once typeset in small caps (''Unix''). According to
Dennis Ritchie Dennis MacAlistair Ritchie (September 9, 1941 – October 12, 2011) was an American computer scientist. He created the C programming language and, with long-time colleague Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an Ame ...
, when presenting the original Unix paper to the third Operating Systems Symposium of the American Association for Computing Machinery (ACM), "we had a new typesetter and ''
troff troff (), short for "typesetter roff", is the major component of a document processing system developed by AT&T Corporation AT&T Corporation, originally the American Telephone and Telegraph Company, is the subsidiary of AT&T Inc. that prov ...
'' had just been invented and we were intoxicated by being able to produce small caps". Many of the operating system's predecessors and contemporaries used all-uppercase lettering, so many people wrote the name in upper case due to force of habit. It is not an acronym. Trademark names can be registered by different entities in different countries and trademark laws in some countries allow the same trademark name to be controlled by two different entities if each entity uses the trademark in easily distinguishable categories. The result is that Unix has been used as a brand name for various products including bookshelves, ink pens, bottled glue, diapers, hair driers and food containers. Several plural forms of Unix are used casually to refer to multiple brands of Unix and Unix-like systems. Most common is the conventional ''Unixes'', but ''Unices'', treating Unix as a Latin noun of the Latin declension#Third declension (i), third declension, is also popular. The pseudo-Anglo-Saxon language, Anglo-Saxon plural form ''Unixen'' is not common, although occasionally seen.
Sun Microsystems Sun Microsystems, Inc. (Sun for short) is a defunct American company that sold computers, computer components, software, and information technology services and created the Java (programming language), Java programming language, the Solaris oper ...
, developer of the Solaris variant, has asserted that the term ''Unix'' is itself plural, referencing its many implementations.


See also

* Comparison of operating systems and Comparison of open-source and closed-source software, free and proprietary software * List of operating systems, List of Unix systems, Unix systems, and List of Unix commands, Unix commands * Usage share of operating systems, Market share of operating systems * Timeline of operating systems * Plan 9 from Bell Labs * Unix time * Year 2038 problem


References


Further reading

;General * * * * * John Lions, Lions, John: ''Lions' with Source Code'', Peer-to-Peer Communications, 1996; ;Books * Peter H. Salus, Salus, Peter H.: ''A Quarter Century of UNIX'', Addison Wesley, June 1, 1994; ;Television * Computer Chronicles (1985).
UNIX
. * Computer Chronicles (1989).
Unix
. ;Talks * *


External links


The UNIX Standard
at
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 ...
. * *
The Unix Tree: files from historic releases

Unix History Repository
— a git repository representing a reconstructed version of the Unix history *
The Unix 1st Edition Manual
*
1st Edition manual rendered to HTML
* (film about Unix featuring Dennis Ritchie, Ken Thompson, Brian Kernighan, Alfred Aho, and more) * (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