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Unix (; trademarked as UNIX) is a family of multitasking,
multiuser Multi-user software is computer software that allows access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving t ...
computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by
Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science. Thompson worked at Bell Labs for most of his career where he designed and implemented the original Unix operating system. He also invented the B programmi ...
, Dennis Ritchie, and others. Initially intended for use inside the Bell System, AT&T licensed 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 land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...
( BSD), Microsoft ( Xenix), Sun Microsystems ( SunOS/ Solaris), HP/ HPE ( HP-UX), and IBM ( AIX). In the early 1990s, AT&T sold its rights in Unix to Novell, which then sold the UNIX trademark to
The Open Group The Open Group is a global consortium that seeks to "enable the achievement of business objectives" by developing "open, vendor-neutral technology standards and certifications." It has over 840 member organizations and provides a number of servi ...
, an industry consortium founded in 1996. The Open Group allows the use of the mark for certified operating systems that comply with the Single UNIX Specification (SUS). Unix systems are characterized by a modular design that is sometimes called the " Unix philosophy". 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-based
filesystem In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is Computer data storage, stored and retrieved. Without a file system, data placed in a storage me ...
(the Unix filesystem) and an inter-process communication mechanism known as "
pipes Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circula ...
" serve as the main means of communication, and a
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
scripting and command language (the
Unix shell A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating syste ...
) is used to combine the tools to perform complex workflows. Unix distinguishes itself from its predecessors as the first portable operating system: almost the entire operating system is written in the C programming language, 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 or for multi-tasking. Later, Unix gradually gained portability, multi-tasking and
multi-user Multi-user software is computer software that allows access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving t ...
capabilities in a time-sharing configuration. Unix systems are characterized by various concepts: the use of
plain text In computing, plain text is a loose term for data (e.g. file contents) that represent only characters of readable material but not its graphical representation nor other objects (floating-point numbers, images, etc.). It may also include a limit ...
for storing data; a hierarchical file system; treating devices and certain types of inter-process communication (IPC) as files; and the use of a large number of software tools, small programs that can be strung together through a
command-line interpreter A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
using
pipes Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circula ...
, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are collectively known as the " Unix philosophy".
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" Pike (born 1956) is a Canadian programmer and author. He is best known for his work on the Go (programming language), Go programming language and at Bell Labs, where he was a member of the Unix team and was involved in the creation o ...
summarize this in '' The Unix Programming Environment'' 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 computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
and the reshaping of computing as centered in
networks Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...
rather than in individual computers. Both Unix and the C programming language 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 central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learn ...
. The kernel provides services to start and stop programs, handles the file system 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 user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...
, 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 The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...
, Bell Labs, and General Electric were developing Multics, a time-sharing 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. Thompson worked at Bell Labs for most of his career where he designed and implemented the original Unix operating system. He also invented the B programmi ...
, Dennis Ritchie,
Douglas McIlroy Malcolm Douglas McIlroy (born 1932) is a mathematician, engineer, and programmer. As of 2019 he is an Adjunct Professor of Computer Science at Dartmouth College. McIlroy is best known for having originally proposed Unix pipelines and developed se ...
, and Joe Ossanna, 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 A 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 rhetorical effect. These ambiguities can arise from the intentional use of homophoni ...
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, but in 1973, Version 4 Unix was rewritten in C. Version 4 Unix, however, still had many PDP-11 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. 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 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 ''Resear ...
''. In 1975, the first source license for ''UNIX'' was sold to Donald B. Gillies at the
University of Illinois Urbana–Champaign The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Universit ...
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 and
System V Unix System V (pronounced: "System Five") is one of the first commercial versions of the Unix operating system. It was originally developed by AT&T and first released in 1983. Four major versions of System V were released, numbered 1, 2, 3, an ...
) by commercial startups, which in turn led to Unix fragmenting into multiple, similar but often slightly mutually-incompatible systems including DYNIX, HP-UX, SunOS/ Solaris, AIX, and 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 developed System V Release 4 ( SVR4), which was subsequently adopted by many commercial Unix vendors. In the 1990s, Unix and Unix-like 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 Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, w ...
distributions were developed through collaboration by a worldwide network of programmers. In 2000, Apple released Darwin, also a Unix system, which became the core of the Mac OS X operating system, later renamed macOS. Unix-like operating systems are widely used in modern servers, workstations, and mobile devices.


Standards

In the late 1980s, an open operating system standardization effort now known as POSIX provided a common baseline for all operating systems; IEEE 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 (COSE) initiative, which eventually became the Single UNIX Specification (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, vendor-neutral technology standards and certifications." It has over 840 member organizations and provides a number of servi ...
. 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 group formed to develop and maintain a common revision of POSIX.1 and parts of the Single UNIX Specification. It is named after the location of the first ...
, 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 (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 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 central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learn ...
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, earning its reputation as a portable system. 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 compiler (first appeared in V3 Unix) ** ''as'' machine-language assembler for the machine ** ''ld''
linker Linker or linkers may refer to: Computing * Linker (computing), a computer program that takes one or more object files generated by a compiler or generated by an assembler and links them with libraries, generating an executable program or shar ...
, 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 for the C programming language, as specified in the ISO C standard. ISO/IEC (2018). '' ISO/IEC 9899:2018(E): Programming Languages - C §7'' Starting from the original ANSI C standard, it was ...
'', 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 d ...
'') 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), a tech DIY periodical *Make (software), a software build tool *Make, Botswana, in the Kalahari Desert *Make Architects Make Architects is an international architecture practice headquartered in Londo ...
'' build manager (introduced in PWB/UNIX), 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 language designed for text processing and typically used as a data extraction and reporting tool. Like sed and grep, it is a filter, and is a standard feature of most Unix-like operating systems. The AWK lang ...
scripting language; later versions and implementations contain many other language compilers and toolsets. Early BSD releases included Pascal tools, and many modern Unix systems also include the GNU Compiler Collection 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 Lex or LEX may refer to: Arts and entertainment * ''Lex'', a daily featured column in the ''Financial Times'' Games * Lex, the mascot of the word-forming puzzle video game ''Bookworm'' * Lex, the protagonist of the word-forming puzzle video ga ...
'' & '' yacc''), and debugging tools. * ''Commands'' Unix makes little distinction between commands (user-level programs) for system operation and maintenance (e.g. '' cron''), 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 command ''g/re/p'' (''globally search for a regular expression and print matching lines''), which has the sa ...
''), 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 interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
, 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'', '' ls'', ''
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 command ''g/re/p'' (''globally search for a regular expression and print matching lines''), which has the sa ...
'', ''
find Find, FIND or Finding may refer to: Computing * find (Unix), a command on UNIX platforms * find (Windows), a command on DOS/Windows platforms Books * ''The Find'' (2010), by Kathy Page * ''The Find'' (2014), by William Hope Hodgson Film and t ...
'' 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 Unix and Unix-like operating systems, such as Linux, macOS, and FreeBSD. A similar command, CHKDSK, exists in Microsoft Windows ...
'', 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'', ''
troff troff (), short for "typesetter roff", is the major component of a document processing system developed by Bell Labs for the Unix operating system. troff and the related nroff were both developed from the original roff. While nroff was inte ...
'', ''
tbl Part of the troff suite of Unix document layout tools, tbl is a preprocessor that formats tables in preparation for processing with troff/nroff. Overview Mike Lesk is the original author of tbl. Like the main troff program, it uses command l ...
'', '' eqn'', '' refer'', and '' pic''. Some modern Unix systems also include packages such as
TeX Tex may refer to: People and fictional characters * Tex (nickname), a list of people and fictional characters with the nickname * Joe Tex (1933–1982), stage name of American soul singer Joseph Arrington Jr. Entertainment * ''Tex'', the Italian ...
and
Ghostscript Ghostscript is a suite of software based on an interpreter for Adobe Systems' PostScript and Portable Document Format (PDF) page description languages. Its main purposes are the rasterization or rendering of such page description language file ...
. ** ''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 wi ...
as a standard windowing system and GUI, and many support OpenGL. ** ''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 of Unix-to-Unix Copy. The term generally refers to a suite of computer programs and protocols allowing remote execution of commands and transfer of files, email and netnews between computers. A command named is one of the pr ...
, and systems beginning with BSD release 4.1c included TCP/IP utilities. * ''Documentation'' Unix was one of the first operating systems to include all of its documentation online in machine-readable form. The documentation included: ** ''
man A man is an adult male human. Prior to adulthood, a male human is referred to as a boy (a male child or adolescent). Like most other male mammals, a man's genome usually inherits an X chromosome from the mother and a Y chromo ...
'' manual pages for each command, library component,
system call In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, acc ...
, 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, but was soon rewritten in C, a high-level programming language. Although this followed the lead of CTSS, Multics and Burroughs MCP, 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 drives), providing a uniform interface, but at the expense of occasionally requiring additional mechanisms such as ioctl 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 ...
's "group, user" hierarchy evolved into OpenVMS directories, CP/M's volumes evolved into MS-DOS 2.0+ subdirectories, and HP's MPE group.account hierarchy and IBM's SSP and OS/400 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 for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating syste ...
used the same language for interactive commands as for scripting ( shell scripts – there was no separate job control language like IBM's 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 ( pipelines) made a powerful programming paradigm (
coroutine Coroutines are computer program components that generalize subroutines for non-preemptive multitasking, by allowing execution to be suspended and resumed. Coroutines are well-suited for implementing familiar program components such as cooperative ...
s) 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- 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-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 protocols The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
, e.g., FTP,
SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients ty ...
, HTTP,
SOAP Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...
, and SIP. Unix popularized a syntax for
regular expression A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" ...
s 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 soon spread beyond Unix, and is now ubiquitous in systems and applications programming. Early Unix developers were important in bringing the concepts of modularity and
reusability In computer science and software engineering, reusability is the use of existing ''assets'' in some form within the software product development process; these ''assets'' are products and by-products of the software development life cycle and in ...
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 TCP/IP networking protocols were quickly implemented on the Unix versions widely used on relatively inexpensive computers, which contributed to the
Internet The 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'' that consists of private, pub ...
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 The free software movement is a social movement with the goal of obtaining and guaranteeing certain freedoms for software users, namely the freedoms to run the software, to study the software, to modify the software, and to share copies of the s ...
in 1983.


Free Unix and Unix-like variants

In 1983, Richard Stallman announced the
GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...
(short for "GNU's Not Unix") project, an ambitious effort to create a free software Unix-like 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 The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general ...
. In addition to their use in the
GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...
operating system, many GNU packages – such as the GNU Compiler Collection (and the rest of the GNU toolchain), the GNU C library and the
GNU core utilities The GNU Core Utilities or coreutils is a package of GNU software containing implementations for many of the basic tools, such as cat, ls, and rm, which are used on Unix-like operating systems. In September 2002, the ''GNU coreutils'' were ...
 – 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, SUSE Linux Enterprise,
openSUSE openSUSE () is a free and open source RPM-based Linux distribution developed by the openSUSE project. The initial release of the community project was a beta version of SUSE Linux 10.0. Additionally the project creates a variety of tools, s ...
, Debian, Ubuntu,
Linux Mint Linux Mint is a community-driven Linux distribution based on Ubuntu (which is in turn based on Debian), bundled with a variety of free and open-source applications. It can provide full out-of-the-box multimedia support for those who choose to i ...
, Mandriva Linux,
Slackware Linux Slackware is a Linux distribution created by Patrick Volkerding in 1993. Originally based on Softlanding Linux System, Slackware has been the basis for many other Linux distributions, most notably the first versions of SUSE Linux distributions ...
,
Arch Linux Arch Linux () is an independently developed, x86-64 general-purpose Linux distribution that strives to provide the latest stable versions of most software by following a rolling-release model. The default installation is a minimal base system, ...
and Gentoo. A free derivative of BSD Unix,
386BSD 386BSD (also known as "Jolix") is a discontinued Unix operating system based on the Berkeley Software Distribution (BSD). It was released in 1992 and ran on PC-compatible computer systems based on the 32-bit Intel 80386 microprocessor. 386BSD inn ...
, 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 wh ...
, 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, which included a CDDL-licensed kernel and a primarily
GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...
userland. However, 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 Illumos (stylized as illumos) is a partly free and open-source Unix operating system. It is based on OpenSolaris, which was based on System V Release 4 (SVR4) and the Berkeley Software Distribution (BSD). Illumos comprises a kernel, device d ...
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 University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Univers ...
. The Unix system was said to "present several interesting capabilities as an ARPANET mini-host". At the time, Unix required a license from
Bell Telephone Laboratories Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...
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
compilers In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
, an editor based on QED, a versatile document preparation system, and an efficient file system featuring sophisticated access control, mountable and de-mountable volumes, and a unified treatment of peripherals as special files." The latter permitted the Network Control Program (NCP) to be integrated within the Unix file system, treating network connections as special files that could be accessed through standard Unix I/O calls, which included the added benefit of closing all connections on program exit, should the user neglect to do so. In order "to minimize the amount of code added to the basic Unix
kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learn ...
", much of the NCP code ran in a swappable user process, running only when needed.


Branding

In October 1993, 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, vendor-neutral technology standards and certifications." It has over 840 member organizations and provides a number of servi ...
), and in 1995 sold the related business operations to Santa Cruz Operation (SCO). Whether Novell also sold the copyrights to the actual software was the subject of a federal lawsuit in 2006, ''
SCO v. Novell ''SCO v. Novell'' was a United States lawsuit in which the software company The SCO Group (SCO), claimed ownership of the source code for the Unix operating system. SCO sought to have the court declare that SCO owned the rights to the Unix code, ...
'', 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 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 qualify as "UNIX" (others are called " Unix-like"). 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 Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
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, EulerOS, HP-UX, Inspur K-UX, IRIX, macOS, Solaris, Tru64 UNIX (formerly "Digital UNIX", or OSF/1), and
z/OS z/OS is a 64-bit operating system for IBM z/Architecture mainframes, introduced by IBM in October 2000. It derives from and is the successor to OS/390, which in turn was preceded by a string of MVS versions.Starting with the earliest: * ...
. 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'' always be used as an adjective followed by a generic term such as ''system'' to help avoid the creation of a
genericized trademark A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, because of its popularity or significance, has become the generic term for, or synonymous with, a general class of products ...
. ''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, 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 Bell Labs for the Unix operating system. troff and the related nroff were both developed from the original roff. While nroff was inte ...
'' 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 Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
noun of the third declension, is also popular. The pseudo- Anglo-Saxon plural form ''Unixen'' is not common, although occasionally seen. Sun Microsystems, 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 free and proprietary software * List of operating systems, Unix systems, and Unix commands *
Plan 9 from Bell Labs Plan 9 from Bell Labs is a distributed operating system which originated from the Computing Science Research Center (CSRC) at Bell Labs in the mid-1980s and built on UNIX concepts first developed there in the late 1960s. Since 2000, Plan 9 has be ...
* Timeline of operating systems *
Unix time Current Unix time () Unix time is a date and time representation widely used in computing. It measures time by the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970, the beginning of the Unix epoch, less adjustments m ...
* Market share of operating systems *
Year 2038 problem The year 2038 problem (also known as Y2038, Y2K38, or the Epochalypse) is a time formatting bug in computer systems with representing times after 03:14:07 UTC on 19 January 2038. The problem exists in systems which measure Unix time � ...


References


Further reading

;General * * * * * Lions, John: ''Lions' with Source Code'', Peer-to-Peer Communications, 1996; ;Books * Salus, Peter H.: ''A Quarter Century of UNIX'', Addison Wesley, June 1, 1994; ;Television *
Computer Chronicles ''(The) Computer Chronicles'' is an American half-hour television series, which was broadcast from 1983 to 2002 on Public Broadcasting Service (PBS) public television and which documented various issues from the rise of the personal computer from ...
(1985).
UNIX
. *
Computer Chronicles ''(The) Computer Chronicles'' is an American half-hour television series, which was broadcast from 1983 to 2002 on Public Broadcasting Service (PBS) public television and which documented various issues from the rise of the personal computer from ...
(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, vendor-neutral technology standards and certifications." It has over 840 member organizations and provides a number of servi ...
. * *
The Unix Tree: files from historic releases

Unix History Repository
— a
git Git () is a distributed version control system: tracking changes in any set of files, usually used for coordinating work among programmers collaboratively developing source code during software development. Its goals include speed, data in ...
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 Products introduced in 1969 Operating system families Time-sharing operating systems