Unix
Encyclopedia
Unix is a multitasking
, multi-user
computer operating system
originally developed in 1969 by a group of AT&T
employees at Bell Labs
, including Ken Thompson, Dennis Ritchie
, Brian Kernighan
, Douglas McIlroy
, and Joe Ossanna
. The Unix operating system was first developed in assembly language
, but by 1973 had been almost entirely recoded in C
, greatly facilitating its further development and porting
to other hardware. Today's Unix system evolution is split into various branches, developed over time by AT&T as well as various commercial vendors, universities (such as University of California, Berkeley
's BSD), and non-profit organizations.
The Open Group
, an industry standards consortium, owns the UNIX trademark. Only systems fully compliant with and certified according to the Single UNIX Specification
are qualified to use the trademark; others might be called Unix system-like or Unix-like
, although the Open Group disapproves of this term. However, the term Unix is often used informally to denote any operating system that closely resembles the trademarked system.
During the late 1970s and early 1980s, the influence of Unix in academic circles led to large-scale adoption of Unix (particularly of the BSD
variant, originating from the University of California, Berkeley
) by commercial startups, the most notable of which are Solaris
, HP-UX
and AIX
. Among all variants of Unix, Linux
is the most widely used, powering everything from huge data centers to desktop systems to mobile phones to embedded devices such as routers. Today, in addition to certified Unix systems such as those already mentioned, Unix-like
operating systems such as MINIX
, Linux
, Android, and BSD descendants (FreeBSD
, NetBSD
, OpenBSD
, and DragonFly BSD
) are commonly encountered. The term traditional Unix may be used to describe a Unix or an operating system that has the characteristics of either Version 7 Unix
or UNIX System V
.
s, workstation
s, and mobile devices. The Unix environment and the client–server program model were essential elements in the development of the Internet
and the reshaping of computing as centered in networks rather than in individual computers.
Originally, Unix was meant to be a programmer's workbench more than to be used to run application software. The system grew larger as the operating system started spreading in the academic circle, as users added their own tools to the system and shared them with colleagues.
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. As a result, Unix became synonymous with open systems
.
Unix was designed to be portable
, multi-tasking
and multi-user
in a time-sharing
configuration. Unix systems are characterized by various concepts: the use of plain text
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 tool
s, small programs that can be strung together through a command line interpreter using pipe
s, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are collectively known as the Unix philosophy
. Kernighan and Pike 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."
Under Unix, the operating system consists of many utilities along with the master control program, the kernel. 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 division between user-space and kernel-space.
The microkernel
concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a standard computer consisted of a hard disk for storage and a data terminal for input and output (I/O), the Unix file model worked quite well, as most I/O was linear. However, modern systems include networking and other new devices. As graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse
. In the 1980s non-blocking I/O and the set of inter-process communication
mechanisms were augmented with (Unix domain socket
s, shared memory
, message queue
s, semaphore
s). Functions such as network protocols were moved out of the kernel.
, AT&T Bell Labs, and General Electric
developed an experimental operating system called Multics
for the GE-645
mainframe.
Multics introduced many innovations, but had many problems.
Bell Labs
, frustrated by the size and complexity of Multics but not the aims, slowly pulled out of the project. Their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale.
At the time, Ritchie says "What we wanted to preserve was not just a good environment in which to do programming, but a system around which a fellowship could form. We knew from experience that the essence of communal computing, as supplied by remote-access, time-shared machines, is not just to type programs into a terminal instead of a keypunch, but to encourage close communication."
While Ken Thompson still had access to the Multics environment, he wrote simulations for the new file and paging system on it.
He also programmed a game called Space Travel
, but the game needed a more efficient and less expensive machine to run on, and eventually a little-used PDP-7
at Bell Labs fit the bill.
On this PDP-7, a team of Bell Labs researchers led by Thompson and Ritchie, including Rudd Canaday, developed a hierarchical file system, the concepts of computer processes
and device files, a command-line interpreter, and some small utility programs.
on Multics, (Multiplexing Information and Computer Services). Unics could eventually support multiple simultaneous users, and it was renamed Unix.
Up until this point there had been no financial support from Bell Labs. When the Computer Science Research Group wanted to use Unix on a much larger machine than the PDP-7, Thompson and Ritchie managed to trade the promise of adding text processing capabilities to Unix for a PDP-11/20 machine. This led to some financial support from Bell. For the first time in 1970, the Unix operating system was officially named and ran on the PDP-11/20. It added a text formatting program called roff
and a text editor
. All three were written in PDP-11/20 assembly language. Bell Labs used this initial text processing system, consisting of Unix, roff, and the editor, for text processing of patent
applications. Roff soon evolved into troff
, the first electronic publishing program with a full typesetting
capability. The UNIX Programmer's Manual was published on November 3, 1971.
In 1972, Unix was rewritten in the C programming language
, contrary to the general notion at the time "that something as complex as an operating system, which must deal with time-critical events, had to be written exclusively in assembly language". The migration from assembly language
to the higher-level language
C resulted in much more portable software, requiring only a relatively small amount of machine-dependent code to be replaced when porting Unix to other computing platforms
.
Under a 1958 consent decree in settlement of an antitrust case, AT&T (the parent organization of Bell Labs) had been forbidden from entering the computer business. Unix could not, therefore, be turned into a product; indeed, under the terms of the consent decree, Bell Labs was required to license its non-telephone technology to anyone who asked. Ken Thompson quietly began answering requests by shipping out tapes and disk packs – each, according to legend, with a note signed "love, ken”.
AT&T made Unix available to universities and commercial firms, as well as the United States government, under licenses. The licenses included all source code including the machine-dependent parts of the kernel, which were written in PDP-11 assembly code. Copies of the annotated Unix kernel sources circulated widely in the late 1970s in the form of a much-copied book by John Lions
of the University of New South Wales
, the Lions' Commentary on UNIX 6th Edition, with Source Code
, which led to considerable use of Unix as an educational example.
Versions of the Unix system were determined by editions of its user manuals. For example, "Fifth Edition UNIX" and "UNIX Version 5" have both been used to designate the same version. Development expanded, with Versions 4, 5, and 6
being released by 1975. These versions added the concept of pipes, which led to the development of a more modular code-base and quicker development cycles. Version 5 and especially Version 6 led to a plethora of different Unix versions both inside and outside Bell Labs, including PWB/UNIX
and the first commercial Unix, IS/1
. As more of Unix was rewritten in C, portability also increased. A group at the University of Wollongong
ported Unix
to the Interdata 7/32. Bell Labs developed several ports for research purposes and internal use at AT&T. Target machines included an Intel 8086
-based computer (with custom-built MMU
) and the UNIVAC 1100.
In May 1975 ARPA documented the benefits of the Unix time-sharing system which "presents several interesting capabilities" as an ARPA network
mini-host in RFC 681.
In 1978, UNIX/32V
was released for DEC
's then new VAX
system. By this time, over 600 machines were running Unix in some form. Version 7 Unix
, the last version of Research Unix
to be released widely, was released in 1979. Versions 8
, 9
and 10
were developed through the 1980s but were only released to a few universities, though they did generate papers describing the new work. This research led to the development of Plan 9 from Bell Labs
, a new portable distributed system.
AT&T licensed UNIX System III
, based largely on Version 7, for commercial use, the first version launching in 1982. This also included support for the VAX. AT&T continued to issue licenses for older Unix versions. To end the confusion between all its differing internal versions, AT&T combined them into UNIX System V
Release 1. This introduced a few features such as the vi
editor and curses
from the Berkeley Software Distribution
of Unix developed at the University of California, Berkeley
. This also included support for the Western Electric
3B series of machines. AT&T provided support for System III and System V through the Unix Support Group (USG), and these systems were sometimes referred to as USG Unix.
In 1983, the U.S. Department of Justice settled its second antitrust case against AT&T and broke up the Bell System. This relieved AT&T from the 1958 consent decree that had prevented them from turning Unix into a product. AT&T promptly rushed to commercialize Unix System V, a move that nearly killed Unix. The GNU Project
was founded the same year by Richard Stallman
.
Since the newer commercial UNIX licensing terms were not as favorable for academic use as the older versions of Unix, the Berkeley researchers continued to develop BSD Unix as an alternative to UNIX System III and V, originally on the PDP-11 architecture (the 2.xBSD releases, ending with 2.11BSD) and later for the VAX-11 (the 4.x BSD releases). Many contributions to Unix first appeared on BSD releases, notably the C shell
with job control (modelled on ITS). Perhaps the most important aspect of the BSD development effort was the addition of TCP/IP network
code to the mainstream Unix kernel. The BSD effort produced several significant releases that contained network code: 4.1cBSD, 4.2BSD, 4.3BSD, 4.3BSD-Tahoe ("Tahoe" being the nickname of the Computer Consoles Inc.
Power 6/32 architecture that was the first non-DEC release of the BSD kernel), Net/1, 4.3BSD-Reno (to match the "Tahoe" naming, and that the release was something of a gamble), Net/2, 4.4BSD, and 4.4BSD-lite. The network code found in these releases is the ancestor of much TCP/IP network code in use today, including code that was later released in AT&T System V UNIX and early versions of Microsoft Windows
. The accompanying Berkeley sockets
API
is a de facto standard for networking APIs and has been copied on many platforms.
Other companies began to offer commercial versions of the UNIX System for their own mini-computers and workstations. Most of these new Unix flavors were developed from the System V base under a license from AT&T; however, others were based on BSD instead. One of the leading developers of BSD, Bill Joy
, went on to co-found Sun Microsystems
in 1982 and created SunOS
for their workstation
computers. In 1980, Microsoft
announced its first Unix for 16-bit
microcomputers called Xenix
, which the Santa Cruz Operation (SCO) ported to the Intel 8086
processor in 1983, and eventually branched Xenix into SCO UNIX in 1989.
During this period (before PC compatible computers with MS-DOS
became dominant), industry observers expected that UNIX, with its portability and rich capabilities, was likely to become the industry standard operating system for microcomputers. In 1984 several companies established the X/Open
consortium with the goal of creating an open system specification based on UNIX. Despite early progress, the standardization effort collapsed into the "Unix wars
", with various companies forming rival standardization groups. The most successful Unix-related standard turned out to be the IEEE's POSIX
specification, designed as a compromise API
readily implemented on both BSD and System V platforms, published in 1988 and soon mandated by the United States government for many of its own systems.
AT&T added various features into UNIX System V, such as file locking
, system administration, STREAMS
, new forms of IPC
, the Remote File System
and TLI
. AT&T cooperated with Sun Microsystems and between 1987 and 1989 merged features from Xenix
, BSD, SunOS, and System V into System V Release 4 (SVR4), independently of X/Open. This new release consolidated all the previous features into one package, and heralded the end of competing versions. It also increased licensing fees.
During this time a number of vendors including Digital Equipment, Sun, Addamax
and others began building trusted versions
of UNIX for high security applications, mostly designed for military and law enforcement applications.
released OSF/1, their standard Unix implementation, based on Mach and BSD. The Foundation was started in 1988 and was funded by several Unix-related companies that wished to counteract the collaboration of AT&T and Sun on SVR4. Subsequently, AT&T and another group of licensees formed the group UNIX International
in order to counteract OSF. This escalation of conflict between competing vendors again gave rise to the phrase Unix wars.
In 1991, a group of BSD developers (Donn Seeley, Mike Karels, Bill Jolitz, and Trent Hein) left the University of California to found Berkeley Software Design, Inc (BSDI
). BSDI produced a fully functional commercial version of BSD Unix for the inexpensive and ubiquitous Intel platform, which started a wave of interest in the use of inexpensive hardware for production computing. Shortly after it was founded, Bill Jolitz left BSDI to pursue distribution of 386BSD
, the free software ancestor of FreeBSD
, OpenBSD
, and NetBSD
.
In 1991, Linus Torvalds began work on Linux
, a Unix clone that initially ran on IBM PC compatible
computers.
By 1993 most commercial vendors had changed their variants of Unix to be based on System V with many BSD features added. The creation of the Common Open Software Environment (COSE) initiative that year by the major players in Unix marked the end of the most notorious phase of the Unix wars, and was followed by the merger of UI and OSF in 1994. The new combined entity, which retained the OSF name, stopped work on OSF/1. By that time the only vendor using it was Digital Equipment Corporation
, which continued its own development, rebranding their product Digital UNIX in early 1995.
Shortly after UNIX System V Release 4 was produced, AT&T sold all its rights to UNIX to Novell
. Dennis Ritchie likened this sale to the Biblical story of Esau
selling his birthright for the proverbial mess of pottage
. Novell developed its own version, UnixWare
, merging its NetWare with UNIX System V Release 4. Novell tried to use this as a marketing tool against Windows NT
, but their core markets suffered considerably.
In 1993, Novell decided to transfer the UNIX trademark
and certification rights to the X/Open
Consortium. In 1996, X/Open merged with OSF
, creating the Open Group. Various standards by the Open Group now define what is and what is not a UNIX operating system, notably the post-1998 Single UNIX Specification
.
In 1995, the business of administering and supporting the existing UNIX licenses, plus rights to further develop the System V code base, were sold by Novell to the Santa Cruz Operation. Whether Novell also sold the copyrights is currently the subject of litigation (see below).
In 1997, Apple Computer
sought out a new foundation for its Macintosh operating system and chose NEXTSTEP
, an operating system developed by NeXT
. The core operating system, which was based on BSD and the Mach kernel, was renamed Darwin
after Apple acquired it. The deployment of Darwin in Mac OS X
makes it, according to a statement made by an Apple employee at a USENIX
conference, the most widely used Unix-based system in the desktop computer
market.
The bursting of the dot-com bubble
(2001–2003) led to significant consolidation of versions of Unix. Of the many commercial variants of Unix that were born in the 1980s, only Solaris
, HP-UX
, and AIX
were still doing relatively well in the market, though SGI's IRIX
persisted for quite some time. Of these, Solaris had the largest market share in 2005.
In 2003, the SCO Group started legal action against various users and vendors of Linux. SCO had alleged that Linux contained copyrighted Unix code now owned by The SCO Group. Other allegations included trade-secret violations by IBM
, or contract violations by former Santa Cruz customers who had since converted to Linux. However, Novell disputed the SCO Group's claim to hold copyright on the UNIX source base. According to Novell, SCO (and hence the SCO Group) are effectively franchise operators for Novell, which also retained the core copyrights, veto rights over future licensing activities of SCO, and 95% of the licensing revenue. The SCO Group disagreed with this, and the dispute resulted in the SCO v. Novell
lawsuit. On August 10, 2007, a major portion of the case was decided in Novell's favor (that Novell had the copyright to UNIX, and that the SCO Group had improperly kept money that was due to Novell). The court also ruled that "SCO is obligated to recognize Novell's waiver of SCO's claims against IBM and Sequent". After the ruling, Novell announced they have no interest in suing people over Unix and stated, "We don't believe there is Unix in Linux". SCO successfully got the 10th Circuit Court of Appeals to partially overturn this decision on August 24, 2009 which sent the lawsuit back to the courts for a jury trial.
On March 30, 2010, following a jury trial, Novell, and not The SCO Group, was "unanimously [found]" to be the owner of the UNIX and UnixWare copyrights. The SCO Group, through bankruptcy trustee Edward Cahn, decided to continue the lawsuit against IBM for causing a decline in SCO revenues.
In 2005, Sun Microsystems
released the bulk of its Solaris system code (based on UNIX System V
Release 4) into an open source
project called OpenSolaris
. New Sun OS technologies, notably the ZFS
file system, were first released as open source code via the OpenSolaris project. Soon afterwards, OpenSolaris spawned several non-Sun distributions. In 2010, after Oracle acquired Sun, OpenSolaris was officially discontinued, but the development of derivatives continued.
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
administered by The Open Group
. Starting in 1998 the Open Group and IEEE started the Austin Group
, to provide a common definition of POSIX and the Single UNIX Specification.
In an effort towards compatibility, in 1999 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 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, particularly Linux.
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 10MB, and arrived on a single 9-track magnetic tape
. The printed documentation, typeset from the on-line 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:
It was written in high level language rather than assembly language
(which had been thought necessary for systems implementation on early computers). Although this followed the lead of Multics
and Burroughs, 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 printer
s, terminal
s, 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-11
M's "group, user" hierarchy evolved into VMS 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
used the same language for interactive commands as for scripting (shell script
s – 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) his 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
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 ASCII 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
, e.g., FTP, SMTP, HTTP, SOAP
and 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
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
into software engineering
practice, spawning a "software tools" movement.
Unix provided the TCP/IP networking protocol on relatively inexpensive computers, which contributed to the Internet
explosion of worldwide real-time connectivity, and which formed the basis for implementations on many other platforms. This also exposed numerous security holes in the networking implementations.
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 1983 launch of the free software 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
.
announced the GNU
project, an ambitious effort to create a free software
Unix-like
system; "free" in 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 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/Linux 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 – have gone on to play central roles in other free Unix systems as well.
Linux distributions, comprising Linux 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
, Debian GNU/Linux
, Ubuntu
, Mandriva Linux
, Slackware Linux and Gentoo
.
A free derivative of BSD Unix, 386BSD
, was also released in 1992 and led to the NetBSD
and FreeBSD
projects. With the 1994 settlement of a lawsuit that UNIX Systems Laboratories brought against the University of California and Berkeley Software Design Inc. (USL v. BSDi
), 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 directions, including OpenBSD
and DragonFly BSD
.
Linux and BSD are now rapidly occupying much of the market traditionally occupied by proprietary Unix operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. Due to the modularity of the Unix design, sharing bits and pieces is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and modern systems also usually include some GNU utilities in their distributions.
OpenSolaris
is a relatively recent addition to the list of operating systems based on free software licenses marked as such by FSF
and OSI
. It includes a number of derivatives that combines CDDL-licensed kernel and system tools and also GNU
userland and is currently the only open source System V derivative available.
.
Since times before 1970 are rarely represented in Unix time
, one possible solution that is compatible with existing binary formats would be to redefine
merely postpones the problem to February 7, 2106, and could introduce bugs in software that computes time differences.
Some Unix versions have already addressed this. For example, in Solaris and Linux in 64-bit mode,
mini-host. The evaluation process was also documented. Unix required a license that was very expensive with $20,000(US) for non-university
users and $150 for an educational license. It was noted that for an ARPA network-wide license Bell "were open to suggestions in that area".
Specific features found beneficial were:
, the company that owned the rights to the Unix System V source at the time, transferred the trademark
s of Unix to the X/Open Company (now The Open Group
), and in 1995 sold the related business operations to Santa Cruz Operation. Whether Novell also sold the copyright
s to the actual software was the subject of a 2006 federal lawsuit, SCO v. Novell
, which Novell won. The case was appealed, but on Aug 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 system-like" or "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 or UNIX 03 trademarks today, after the operating system's vendor pays a fee to The Open Group. Systems licensed to use the UNIX trademark include AIX, HP-UX
, IRIX
, Solaris, Tru64 (formerly "Digital UNIX"), A/UX
, Mac OS X
, and a part of z/OS
.
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, e.g. Linux
, BSD, etc., 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 "U "font-variant:small-caps">NIX" remains widespread because, according to Dennis Ritchie
, when presenting the original Unix paper to the third Operating Systems Symposium of the American Association for Computing Machinery
, “we had a new typesetter and troff
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.
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 third declension, is also popular. The pseudo-Anglo-Saxon plural form Unixen is not common, although occasionally seen. 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 book shelves, ink pens, bottled glue, diapers, hair driers and food containers.
Television
Computer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
, multi-user
Multi-user
Multi-user is a term that defines an operating system or application software that allows concurrent 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 the...
computer operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
originally developed in 1969 by a group of AT&T
American Telephone & Telegraph
AT&T Corp., originally American Telephone and Telegraph Company, is an American telecommunications company that provides voice, video, data, and Internet telecommunications and professional services to businesses, consumers, and government agencies. AT&T is the oldest telecommunications company...
employees at Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
, including Ken Thompson, Dennis Ritchie
Dennis Ritchie
Dennis MacAlistair Ritchie , was an American computer scientist who "helped shape the digital era." He created the C programming language and, with long-time colleague Ken Thompson, the UNIX operating system...
, Brian Kernighan
Brian Kernighan
Brian Wilson Kernighan is a Canadian computer scientist who worked at Bell Labs alongside Unix creators Ken Thompson and Dennis Ritchie and contributed to the development of Unix. He is also coauthor of the AWK and AMPL programming languages. The 'K' of K&R C and the 'K' in AWK both stand for...
, Douglas McIlroy
Douglas McIlroy
Malcolm Douglas McIlroy is a mathematician, engineer, and programmer. As of 2007 he is an Adjunct Professor of Computer Science at Dartmouth College. Dr...
, and Joe Ossanna
Joe Ossanna
Joseph F. Ossanna was a Member of the Technical Staff of the Bell Telephone Laboratories in Murray Hill, New Jersey...
. The Unix operating system was first developed in assembly language
Assembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
, but by 1973 had been almost entirely recoded in C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
, greatly facilitating its further development and porting
Software portability
Portability in high-level computer programming is the usability of the same software in different environments. The prerequirement for portability is the generalized abstraction between the application logic and system interfaces...
to other hardware. Today's Unix system evolution is split into various branches, developed over time by AT&T as well as various commercial vendors, universities (such as University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
's BSD), and non-profit organizations.
The Open Group
The Open Group
The Open Group is a vendor and technology-neutral industry consortium, currently with over three hundred member organizations. It was formed in 1996 when X/Open merged with the Open Software Foundation...
, an industry standards consortium, owns the UNIX trademark. Only systems fully compliant with and certified according to the Single UNIX Specification
Single UNIX Specification
The Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
are qualified to use the trademark; others might be called Unix system-like or Unix-like
Unix-like
A Unix-like 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....
, although the Open Group disapproves of this term. However, the term Unix is often used informally to denote any operating system that closely resembles the trademarked system.
During the late 1970s and early 1980s, the influence of Unix in academic circles led to large-scale adoption of Unix (particularly of the BSD
Berkeley Software Distribution
Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...
variant, originating from the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
) by commercial startups, the most notable of which are Solaris
Solaris Operating System
Solaris is a Unix operating system originally developed by Sun Microsystems. It superseded their earlier SunOS in 1993. Oracle Solaris, as it is now known, has been owned by Oracle Corporation since Oracle's acquisition of Sun in January 2010....
, HP-UX
HP-UX
HP-UX is Hewlett-Packard's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984...
and AIX
AIX operating system
AIX AIX AIX (Advanced Interactive eXecutive, pronounced "a i ex" is a series of proprietary Unix operating systems developed and sold by IBM for several of its computer platforms...
. Among all variants of Unix, Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
is the most widely used, powering everything from huge data centers to desktop systems to mobile phones to embedded devices such as routers. Today, in addition to certified Unix systems such as those already mentioned, Unix-like
Unix-like
A Unix-like 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....
operating systems such as MINIX
Minix
MINIX is a Unix-like computer operating system based on a microkernel architecture created by Andrew S. Tanenbaum for educational purposes; MINIX also inspired the creation of the Linux kernel....
, Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, Android, and BSD descendants (FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
, NetBSD
NetBSD
NetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...
, OpenBSD
OpenBSD
OpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
, and DragonFly BSD
DragonFly BSD
DragonFly BSD is a free Unix-like operating system created as a fork of FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and a FreeBSD developer between 1994 and 2003, began work on DragonFly BSD in June 2003 and announced it on the FreeBSD mailing lists on July...
) are commonly encountered. The term traditional Unix may be used to describe a Unix or an operating system that has the characteristics of either Version 7 Unix
Version 7 Unix
Seventh Edition Unix, also called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercialization of Unix by AT&T in the early 1980s...
or UNIX System V
UNIX System V
Unix System V, commonly abbreviated SysV , is one of the first commercial versions of the Unix operating system. It was originally developed by American Telephone & Telegraph and first released in 1983. Four major versions of System V were released, termed Releases 1, 2, 3 and 4...
.
Overview
Unix operating systems are widely used in serverServer (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
s, workstation
Workstation
A workstation is a high-end microcomputer 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 and run multi-user operating systems...
s, and mobile devices. The Unix environment and the client–server program model were essential elements in the development of the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
and the reshaping of computing as centered in networks rather than in individual computers.
Originally, Unix was meant to be a programmer's workbench more than to be used to run application software. The system grew larger as the operating system started spreading in the academic circle, as users added their own tools to the system and shared them with colleagues.
Both Unix and the C programming language
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
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. As a result, Unix became synonymous with open systems
Open system (computing)
Open systems are computer systems that provide some combination of interoperability, portability, and open software standards. The term was popularized in the early 1980s, mainly to describe systems based on Unix,...
.
Unix was designed to be portable
Porting
In computer science, porting is the process of adapting software so that an executable program can be created for a computing environment that is different from the one for which it was originally designed...
, multi-tasking
Computer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
and multi-user
Multi-user
Multi-user is a term that defines an operating system or application software that allows concurrent 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 the...
in a time-sharing
Time-sharing
Time-sharing is the sharing of a computing resource among many users by means of multiprogramming and multi-tasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major technological shift in the history of computing.By allowing a large...
configuration. Unix systems are characterized by various concepts: the use of plain text
Plain text
In computing, plain text is the contents of an ordinary sequential file readable as textual material without much processing, usually opposed to formatted text....
for storing data; a hierarchical file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
; treating devices and certain types of inter-process communication
Inter-process communication
In computing, Inter-process communication is a set of methods for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC methods are divided into methods for message passing, synchronization, shared...
(IPC) as files; and the use of a large number of software tool
Programming tool
A programming tool or software development tool is a program or application that software developers use to create, debug, maintain, or otherwise support other programs and applications...
s, small programs that can be strung together through a command line interpreter using pipe
Pipeline (Unix)
In Unix-like computer operating systems , a pipeline is the original software pipeline: a set of processes chained by their standard streams, so that the output of each process feeds directly as input to the next one. Each connection is implemented by an anonymous pipe...
s, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are collectively known as the Unix philosophy
Unix philosophy
The Unix philosophy is a set of cultural norms and philosophical approaches to developing software based on the experience of leading developers of the Unix operating system.-McIlroy: A Quarter Century of Unix:...
. Kernighan and Pike summarize this in The Unix Programming Environment
The Unix Programming Environment
The Unix Programming Environment, first published in 1984 by Prentice Hall, is a book written by Brian W. Kernighan and Rob Pike, both of Bell Labs and considered an important and early document of the Unix operating system....
as "the idea that the power of a system comes more from the relationships among programs than from the programs themselves."
Under Unix, the operating system consists of many utilities along with the master control program, the kernel. The kernel provides services to start and stop programs, handles the file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
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 division between user-space and kernel-space.
The microkernel
Microkernel
In computer science, a microkernel is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system . These mechanisms include low-level address space management, thread management, and inter-process communication...
concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a standard computer consisted of a hard disk for storage and a data terminal for input and output (I/O), the Unix file model worked quite well, as most I/O was linear. However, modern systems include networking and other new devices. As graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse
Mouse (computing)
In computing, a mouse is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held under one of the user's hands, with one or more buttons...
. In the 1980s non-blocking I/O and the set of inter-process communication
Inter-process communication
In computing, Inter-process communication is a set of methods for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC methods are divided into methods for message passing, synchronization, shared...
mechanisms were augmented with (Unix domain socket
Unix domain socket
A Unix domain socket or IPC socket is a data communications endpoint for exchanging data between processes executing within the same host operating system. While similar in functionality to...
s, shared memory
Shared memory
In computing, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Depending on context, programs may run on a single processor or on multiple separate processors...
, message queue
Message queue
In computer science, message queues and mailboxes are software-engineering components used for interprocess communication, or for inter-thread communication within the same process. They use a queue for messaging – the passing of control or of content...
s, semaphore
Semaphore (programming)
In computer science, a semaphore is a variable or abstract data type that provides a simple but useful abstraction for controlling access by multiple processes to a common resource in a parallel programming environment....
s). Functions such as network protocols were moved out of the kernel.
History
In the 1960s, the Massachusetts Institute of TechnologyMassachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
, AT&T Bell Labs, and General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
developed an experimental operating system called Multics
Multics
Multics was an influential early time-sharing operating system. The project was started in 1964 in Cambridge, Massachusetts...
for the GE-645
GE-600 series
The GE-600 series was a family of 36-bit mainframe computers originating in the 1960s, built by General Electric . When GE left the mainframe business the line was sold to Honeywell, who built similar systems into the 1990s as the division moved to Groupe Bull and then NEC.-Architecture:The 600...
mainframe.
Multics introduced many innovations, but had many problems.
Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
, frustrated by the size and complexity of Multics but not the aims, slowly pulled out of the project. Their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale.
At the time, Ritchie says "What we wanted to preserve was not just a good environment in which to do programming, but a system around which a fellowship could form. We knew from experience that the essence of communal computing, as supplied by remote-access, time-shared machines, is not just to type programs into a terminal instead of a keypunch, but to encourage close communication."
While Ken Thompson still had access to the Multics environment, he wrote simulations for the new file and paging system on it.
He also programmed a game called Space Travel
Space Travel (video game)
Space Travel was an early computer game that simulated travel in the solar system. It was the development of this game that spurred the development of the Unix operating system. It is sometimes claimed that the unrelated game Spacewar! had led to the development of Unix...
, but the game needed a more efficient and less expensive machine to run on, and eventually a little-used PDP-7
PDP-7
The DEC PDP-7 is a minicomputer produced by Digital Equipment Corporation. Introduced in 1965, it was the first to use their Flip-Chip technology. With a cost of only $72,000 USD, it was cheap but powerful by the standards of the time. The PDP-7 was the third of Digital's 18-bit machines, with...
at Bell Labs fit the bill.
On this PDP-7, a team of Bell Labs researchers led by Thompson and Ritchie, including Rudd Canaday, developed a hierarchical file system, the concepts of computer processes
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
and device files, a command-line interpreter, and some small utility programs.
1970s
In 1970 Peter Neumann coined the project name Unics (UNiplexed Information and Computing Service) as a punWord play
Word play or wordplay is a literary technique in which the words that are used become the main subject of the work, primarily for the purpose of intended effect or amusement...
on Multics, (Multiplexing Information and Computer Services). Unics could eventually support multiple simultaneous users, and it was renamed Unix.
Up until this point there had been no financial support from Bell Labs. When the Computer Science Research Group wanted to use Unix on a much larger machine than the PDP-7, Thompson and Ritchie managed to trade the promise of adding text processing capabilities to Unix for a PDP-11/20 machine. This led to some financial support from Bell. For the first time in 1970, the Unix operating system was officially named and ran on the PDP-11/20. It added a text formatting program called roff
Roff
roff was the first Unix text-formatting computer program, the most important application run on the first machine specifically purchased to run UNIX, and a predecessor of the nroff and troff document processing systems....
and a text editor
Text editor
A text editor is a type of program used for editing plain text files.Text editors are often provided with operating systems or software development packages, and can be used to change configuration files and programming language source code....
. All three were written in PDP-11/20 assembly language. Bell Labs used this initial text processing system, consisting of Unix, roff, and the editor, for text processing of patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
applications. Roff soon evolved into troff
Troff
troff is a document processing system developed by AT&T for the Unix operating system.-History:troff can trace its origins back to a text formatting program called RUNOFF, written by Jerome H. Saltzer for MIT's CTSS operating system in the mid-1960s...
, the first electronic publishing program with a full typesetting
Typesetting
Typesetting is the composition of text by means of types.Typesetting requires the prior process of designing a font and storing it in some manner...
capability. The UNIX Programmer's Manual was published on November 3, 1971.
In 1972, Unix was rewritten in the C programming language
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
, contrary to the general notion at the time "that something as complex as an operating system, which must deal with time-critical events, had to be written exclusively in assembly language". The migration from assembly language
Assembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
to the higher-level language
High-level programming language
A high-level programming language is a programming language with strong abstraction from the details of the computer. In comparison to low-level programming languages, it may use natural language elements, be easier to use, or be from the specification of the program, making the process of...
C resulted in much more portable software, requiring only a relatively small amount of machine-dependent code to be replaced when porting Unix to other computing platforms
Platform (computing)
A computing platform includes some sort of hardware architecture and a software framework , where the combination allows software, particularly application software, to run...
.
Under a 1958 consent decree in settlement of an antitrust case, AT&T (the parent organization of Bell Labs) had been forbidden from entering the computer business. Unix could not, therefore, be turned into a product; indeed, under the terms of the consent decree, Bell Labs was required to license its non-telephone technology to anyone who asked. Ken Thompson quietly began answering requests by shipping out tapes and disk packs – each, according to legend, with a note signed "love, ken”.
AT&T made Unix available to universities and commercial firms, as well as the United States government, under licenses. The licenses included all source code including the machine-dependent parts of the kernel, which were written in PDP-11 assembly code. Copies of the annotated Unix kernel sources circulated widely in the late 1970s in the form of a much-copied book by John Lions
John Lions
John Lions was an Australian computer scientist. He is best known as the author of Lions' Commentary on UNIX 6th Edition, with Source Code, commonly known as the Lions Book.-Early life:...
of the University of New South Wales
University of New South Wales
The University of New South Wales , is a research-focused university based in Kensington, a suburb in Sydney, New South Wales, Australia...
, the Lions' Commentary on UNIX 6th Edition, with Source Code
Lions' Commentary on UNIX 6th Edition, with Source Code
Lions' Commentary on UNIX 6th Edition, with Source Code by John Lions contains the complete source code of the 6th Edition Unix kernel plus a commentary. It is commonly referred to as the Lions book...
, which led to considerable use of Unix as an educational example.
Versions of the Unix system were determined by editions of its user manuals. For example, "Fifth Edition UNIX" and "UNIX Version 5" have both been used to designate the same version. Development expanded, with Versions 4, 5, and 6
Version 6 Unix
Sixth Edition Unix, also called Version 6 Unix or just V6, was the first version of the Unix operating system to see wide release outside Bell Labs. It was released in May 1975 and, like its direct predecessor, targeted the DEC PDP-11 family of minicomputers...
being released by 1975. These versions added the concept of pipes, which led to the development of a more modular code-base and quicker development cycles. Version 5 and especially Version 6 led to a plethora of different Unix versions both inside and outside Bell Labs, including PWB/UNIX
PWB/UNIX
The Programmer's Workbench was an early version of the Unix operating system created in the Bell Labs Computer Science Research Group of AT&T....
and the first commercial Unix, IS/1
INTERACTIVE Systems Corporation
INTERACTIVE Systems Corporation was a US-based software company and the first vendor of the Unix operating system outside AT&T, operating from Santa Monica, CA....
. As more of Unix was rewritten in C, portability also increased. A group at the University of Wollongong
University of Wollongong
The University of Wollongong is a public university located in the coastal city of Wollongong, New South Wales, Australia, approximately 80 kilometres south of Sydney...
ported Unix
Wollongong Unix
A port of Version 6 Unix to the Interdata 7/32 was completed by Richard Miller and Ross Nealon at Wollongong University, Australia, during 1976-1977. This project was supervised by professor Juris Reinfelds. The resulting system was called Wollongong Interdata UNIX, Level 6...
to the Interdata 7/32. Bell Labs developed several ports for research purposes and internal use at AT&T. Target machines included an Intel 8086
Intel 8086
The 8086 is a 16-bit microprocessor chip designed by Intel between early 1976 and mid-1978, when it was released. The 8086 gave rise to the x86 architecture of Intel's future processors...
-based computer (with custom-built MMU
Memory management unit
A memory management unit , sometimes called paged memory management unit , is a computer hardware component responsible for handling accesses to memory requested by the CPU...
) and the UNIVAC 1100.
In May 1975 ARPA documented the benefits of the Unix time-sharing system which "presents several interesting capabilities" as an ARPA network
ARPANET
The Advanced Research Projects Agency Network , was the world's first operational packet switching network and the core network of a set that came to compose the global Internet...
mini-host in RFC 681.
In 1978, UNIX/32V
UNIX/32V
UNIX/32V was an early version of the Unix operating system from Bell Laboratories, released in June 1979. 32V was a direct port of the PDP-11 Seventh Edition Unix to the DEC VAX architecture....
was released for DEC
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
's then new VAX
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
system. By this time, over 600 machines were running Unix in some form. Version 7 Unix
Version 7 Unix
Seventh Edition Unix, also called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercialization of Unix by AT&T in the early 1980s...
, the last version of Research Unix
Research Unix
Research Unix is a term used to refer to 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 Science Research Center ....
to be released widely, was released in 1979. Versions 8
Version 8 Unix
Eighth Edition Unix, also known as Version 8 Unix or V8, was a version of the Research Unix operating system developed and used internally at Bell Labs and a select number of universities. It was "released" in February 1985, ran on VAX hardware, and was a variant of 4.1cBSD with some System V.1 ...
, 9
Version 9 Unix
Ninth Edition Unix, also known as Version 9 Unix or V9, was a version of the Research Unix operating system developed and used internally at the Bell Labs Information Sciences Research Division, "released" in September 1986. V9 was the successor to V8, and the predecessor to the last Research Unix...
and 10
Version 10 Unix
Tenth Edition Unix, also known as Version 10 Unix or V10, was the last version of the Research Unix operating system developed and used internally at Bell Labs. "Released" in 1989, it was the successor of V9...
were developed through the 1980s but were only released to a few universities, though they did generate papers describing the new work. This research led to the development of Plan 9 from Bell Labs
Plan 9 from Bell Labs
Plan 9 from Bell Labs is a distributed operating system. It was developed primarily for research purposes as the successor to Unix by the Computing Sciences Research Center at Bell Labs between the mid-1980s and 2002...
, a new portable distributed system.
1980s
UNIX System III
UNIX System III was a version of the Unix operating system released by AT&T's Unix Support Group . It was first released outside of Bell Labs in 1982. UNIX System III was a mix of various AT&T Unixes: PWB/UNIX 2.0, CB UNIX 3.0, UNIX/TS 3.0.1 and UNIX/32V...
, based largely on Version 7, for commercial use, the first version launching in 1982. This also included support for the VAX. AT&T continued to issue licenses for older Unix versions. To end the confusion between all its differing internal versions, AT&T combined them into UNIX System V
UNIX System V
Unix System V, commonly abbreviated SysV , is one of the first commercial versions of the Unix operating system. It was originally developed by American Telephone & Telegraph and first released in 1983. Four major versions of System V were released, termed Releases 1, 2, 3 and 4...
Release 1. This introduced a few features such as the vi
Vi
vi is a screen-oriented text editor originally created for the Unix operating system. The portable subset of the behavior of vi and programs based on it, and the ex editor language supported within these programs, is described by the Single Unix Specification and POSIX.The original code for vi...
editor and curses
Curses (programming library)
curses is a terminal control library for Unix-like systems, enabling the construction of text user interface applications.The name is a pun on the term “cursor optimization”. It is a library of functions that manage an application's display on character-cell terminals .- Overview :The curses API...
from the Berkeley Software Distribution
Berkeley Software Distribution
Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...
of Unix developed at the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
. This also included support for the Western Electric
Western Electric
Western Electric Company was an American electrical engineering company, the manufacturing arm of AT&T from 1881 to 1995. It was the scene of a number of technological innovations and also some seminal developments in industrial management...
3B series of machines. AT&T provided support for System III and System V through the Unix Support Group (USG), and these systems were sometimes referred to as USG Unix.
In 1983, the U.S. Department of Justice settled its second antitrust case against AT&T and broke up the Bell System. This relieved AT&T from the 1958 consent decree that had prevented them from turning Unix into a product. AT&T promptly rushed to commercialize Unix System V, a move that nearly killed Unix. The GNU Project
GNU Project
The GNU Project is a free software, mass collaboration project, announced on September 27, 1983, by Richard Stallman at MIT. It initiated GNU operating system development in January, 1984...
was founded the same year by Richard Stallman
Richard Stallman
Richard Matthew Stallman , often shortened to rms,"'Richard Stallman' is just my mundane name; you can call me 'rms'"|last= Stallman|first= Richard|date= N.D.|work=Richard Stallman's homepage...
.
Since the newer commercial UNIX licensing terms were not as favorable for academic use as the older versions of Unix, the Berkeley researchers continued to develop BSD Unix as an alternative to UNIX System III and V, originally on the PDP-11 architecture (the 2.xBSD releases, ending with 2.11BSD) and later for the VAX-11 (the 4.x BSD releases). Many contributions to Unix first appeared on BSD releases, notably the C shell
C shell
The C shell is a Unix shell that was created by Bill Joy while a graduate student at University of California, Berkeley in the late 1970s. It has been distributed widely, beginning with the 2BSD release of the BSD Unix system that Joy began distributing in 1978...
with job control (modelled on ITS). Perhaps the most important aspect of the BSD development effort was the addition of TCP/IP network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
code to the mainstream Unix kernel. The BSD effort produced several significant releases that contained network code: 4.1cBSD, 4.2BSD, 4.3BSD, 4.3BSD-Tahoe ("Tahoe" being the nickname of the Computer Consoles Inc.
Computer Consoles Inc.
Computer Consoles Inc. or CCI was a telephony and computer company located in Rochester, New York, USA, which did business first as a private, and then ultimately a public company from 1968 to 1990...
Power 6/32 architecture that was the first non-DEC release of the BSD kernel), Net/1, 4.3BSD-Reno (to match the "Tahoe" naming, and that the release was something of a gamble), Net/2, 4.4BSD, and 4.4BSD-lite. The network code found in these releases is the ancestor of much TCP/IP network code in use today, including code that was later released in AT&T System V UNIX and early versions of Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
. The accompanying Berkeley sockets
Berkeley sockets
The Berkeley sockets application programming interface comprises a library for developing applications in the C programming language that perform inter-process communication, most commonly for communications across a computer network....
API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
is a de facto standard for networking APIs and has been copied on many platforms.
Other companies began to offer commercial versions of the UNIX System for their own mini-computers and workstations. Most of these new Unix flavors were developed from the System V base under a license from AT&T; however, others were based on BSD instead. One of the leading developers of BSD, Bill Joy
Bill Joy
William Nelson Joy , commonly known as Bill Joy, is an American computer scientist. Joy co-founded Sun Microsystems in 1982 along with Vinod Khosla, Scott McNealy and Andy Bechtolsheim, and served as chief scientist at the company until 2003...
, went on to co-found Sun Microsystems
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
in 1982 and created SunOS
SunOS
SunOS is a version of the Unix operating system developed by Sun Microsystems for their workstation and server computer systems. The SunOS name is usually only used to refer to versions 1.0 to 4.1.4 of SunOS...
for their workstation
Workstation
A workstation is a high-end microcomputer 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 and run multi-user operating systems...
computers. In 1980, Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
announced its first Unix for 16-bit
16-bit
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...
microcomputers called Xenix
Xenix
Xenix is a version of the Unix operating system, licensed to Microsoft from AT&T in the late 1970s. The Santa Cruz Operation later acquired exclusive rights to the software, and eventually superseded it with SCO UNIX ....
, which the Santa Cruz Operation (SCO) ported to the Intel 8086
Intel 8086
The 8086 is a 16-bit microprocessor chip designed by Intel between early 1976 and mid-1978, when it was released. The 8086 gave rise to the x86 architecture of Intel's future processors...
processor in 1983, and eventually branched Xenix into SCO UNIX in 1989.
During this period (before PC compatible computers with MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
became dominant), industry observers expected that UNIX, with its portability and rich capabilities, was likely to become the industry standard operating system for microcomputers. In 1984 several companies established the X/Open
X/Open
X/Open Company, Ltd. was a consortium founded by several European UNIX systems manufacturers in 1984 to identify and promote open standards in the field of information technology. More specifically, the original aim was to define a single specification for operating systems derived from UNIX, to...
consortium with the goal of creating an open system specification based on UNIX. Despite early progress, the standardization effort collapsed into the "Unix wars
Unix wars
The Unix wars were the struggles between vendors of the Unix computer operating system in the late 1980s and early 1990s to set the standard for Unix thenceforth.- Origins :...
", with various companies forming rival standardization groups. The most successful Unix-related standard turned out to be the IEEE's POSIX
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
specification, designed as a compromise API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
readily implemented on both BSD and System V platforms, published in 1988 and soon mandated by the United States government for many of its own systems.
AT&T added various features into UNIX System V, such as file locking
File locking
File locking is a mechanism that restricts access to a computer file by allowing only one user or process access at any specific time. Systems implement locking to prevent the classic interceding update scenario ....
, system administration, STREAMS
STREAMS
In computer networking, STREAMS is the native framework in Unix System V for implementing character devices.STREAMS was designed as a modular architecture for implementing full-duplex I/O between kernel or user space processes and device drivers. Its most frequent uses have been in developing...
, new forms of IPC
Inter-process communication
In computing, Inter-process communication is a set of methods for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC methods are divided into methods for message passing, synchronization, shared...
, the Remote File System
Remote File System
The Remote File System was a distributed file system developed by AT&T in the 1980s. It was first delivered with UNIX System V Release 3 .Compared to NFS it made quite different design decisions...
and TLI
Transport Layer Interface
In computer networking, the Transport Layer Interface was the networking API provided by AT&T UNIX System V Release 3 in 1987 and continued into Release 4 . TLI was the System V counterpart to the BSD sockets programming interface, which was also provided in UNIX System V Release 4...
. AT&T cooperated with Sun Microsystems and between 1987 and 1989 merged features from Xenix
Xenix
Xenix is a version of the Unix operating system, licensed to Microsoft from AT&T in the late 1970s. The Santa Cruz Operation later acquired exclusive rights to the software, and eventually superseded it with SCO UNIX ....
, BSD, SunOS, and System V into System V Release 4 (SVR4), independently of X/Open. This new release consolidated all the previous features into one package, and heralded the end of competing versions. It also increased licensing fees.
During this time a number of vendors including Digital Equipment, Sun, Addamax
Addamax
Addamax is an American software company founded in 1986 in Champaign, Illinois by Dr. Peter A. Alsberg. They developed Trusted operating systems based on ATT System V and Berkeley variants of UNIX...
and others began building trusted versions
Trusted operating system
Trusted Operating System generally refers to an operating system that provides sufficient support for multilevel security and evidence of correctness to meet a particular set of government requirements....
of UNIX for high security applications, mostly designed for military and law enforcement applications.
1990s
In 1990, the Open Software FoundationOpen Software Foundation
The Open Software Foundation was a not-for-profit organization founded in 1988 under the U.S. National Cooperative Research Act of 1984 to create an open standard for an implementation of the UNIX operating system.-History:...
released OSF/1, their standard Unix implementation, based on Mach and BSD. The Foundation was started in 1988 and was funded by several Unix-related companies that wished to counteract the collaboration of AT&T and Sun on SVR4. Subsequently, AT&T and another group of licensees formed the group UNIX International
Unix International
Unix International or UI was an association created in 1988 to promote open standards, especially the Unix operating system. Its most notable members were AT&T and Sun Microsystems, and in fact the commonly accepted reason for its existence was as a counterbalance to the Open Software Foundation ,...
in order to counteract OSF. This escalation of conflict between competing vendors again gave rise to the phrase Unix wars.
In 1991, a group of BSD developers (Donn Seeley, Mike Karels, Bill Jolitz, and Trent Hein) left the University of California to found Berkeley Software Design, Inc (BSDI
Berkeley Software Design
Berkeley Software Design Inc. was a corporation which developed, sold licenses for, and supported BSD/OS , a commercial and partially proprietary variant of the BSD Unix operating system for PC compatible computer systems...
). BSDI produced a fully functional commercial version of BSD Unix for the inexpensive and ubiquitous Intel platform, which started a wave of interest in the use of inexpensive hardware for production computing. Shortly after it was founded, Bill Jolitz left BSDI to pursue distribution of 386BSD
386BSD
386BSD, sometimes called "Jolix", was a free Unix-like operating system based on BSD, first released in 1992. It ran on PC compatible computer systems based on the Intel 80386 microprocessor...
, the free software ancestor of FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
, OpenBSD
OpenBSD
OpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
, and NetBSD
NetBSD
NetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...
.
In 1991, Linus Torvalds began work on Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, a Unix clone that initially ran on IBM PC compatible
IBM PC compatible
IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. Such computers used to be referred to as PC clones, or IBM clones since they almost exactly duplicated all the significant features of the PC architecture, facilitated by various manufacturers' ability to...
computers.
By 1993 most commercial vendors had changed their variants of Unix to be based on System V with many BSD features added. The creation of the Common Open Software Environment (COSE) initiative that year by the major players in Unix marked the end of the most notorious phase of the Unix wars, and was followed by the merger of UI and OSF in 1994. The new combined entity, which retained the OSF name, stopped work on OSF/1. By that time the only vendor using it was Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
, which continued its own development, rebranding their product Digital UNIX in early 1995.
Shortly after UNIX System V Release 4 was produced, AT&T sold all its rights to UNIX to Novell
Novell
Novell, Inc. is a multinational software and services company. It is a wholly owned subsidiary of The Attachmate Group. It specializes in network operating systems, such as Novell NetWare; systems management solutions, such as Novell ZENworks; and collaboration solutions, such as Novell Groupwise...
. Dennis Ritchie likened this sale to the Biblical story of Esau
Esau
Esau , in the Hebrew Bible, is the oldest son of Isaac. He is mentioned in the Book of Genesis, and by the minor prophets, Obadiah and Malachi. The New Testament later references him in the Book of Romans and the Book of Hebrews....
selling his birthright for the proverbial mess of pottage
Mess of pottage
The phrase mess of pottage means something of little value, with a pottage being a type of soup. Though it can appear in general use, it is usually associated with the exchange by Esau of his birthright for a meal of lentil stew, as described in Genesis 25:29–34 in the Bible...
. Novell developed its own version, UnixWare
UnixWare
UnixWare is a Unix operating system maintained by The SCO Group . UnixWare is typically deployed as a server rather than desktop. Binary distributions of UnixWare are available for x86 architecture computers. It was originally released by Univel, a jointly owned venture of AT&T's Unix System...
, merging its NetWare with UNIX System V Release 4. Novell tried to use this as a marketing tool against Windows NT
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
, but their core markets suffered considerably.
In 1993, Novell decided to transfer the UNIX trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
and certification rights to the X/Open
X/Open
X/Open Company, Ltd. was a consortium founded by several European UNIX systems manufacturers in 1984 to identify and promote open standards in the field of information technology. More specifically, the original aim was to define a single specification for operating systems derived from UNIX, to...
Consortium. In 1996, X/Open merged with OSF
Open Software Foundation
The Open Software Foundation was a not-for-profit organization founded in 1988 under the U.S. National Cooperative Research Act of 1984 to create an open standard for an implementation of the UNIX operating system.-History:...
, creating the Open Group. Various standards by the Open Group now define what is and what is not a UNIX operating system, notably the post-1998 Single UNIX Specification
Single UNIX Specification
The Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
.
In 1995, the business of administering and supporting the existing UNIX licenses, plus rights to further develop the System V code base, were sold by Novell to the Santa Cruz Operation. Whether Novell also sold the copyrights is currently the subject of litigation (see below).
In 1997, Apple Computer
Apple Computer
Apple Inc. is an American multinational corporation that designs and markets consumer electronics, computer software, and personal computers. The company's best-known hardware products include the Macintosh line of computers, the iPod, the iPhone and the iPad...
sought out a new foundation for its Macintosh operating system and chose NEXTSTEP
NEXTSTEP
NeXTSTEP was the object-oriented, multitasking operating system developed by NeXT Computer to run on its range of proprietary workstation computers, such as the NeXTcube...
, an operating system developed by NeXT
NeXT
Next, Inc. was an American computer company headquartered in Redwood City, California, that developed and manufactured a series of computer workstations intended for the higher education and business markets...
. The core operating system, which was based on BSD and the Mach kernel, was renamed Darwin
Darwin (operating system)
Darwin is an open source POSIX-compliant computer operating system released by Apple Inc. in 2000. It is composed of code developed by Apple, as well as code derived from NeXTSTEP, BSD, and other free software projects....
after Apple acquired it. The deployment of Darwin in Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
makes it, according to a statement made by an Apple employee at a USENIX
USENIX
-External links:* *...
conference, the most widely used Unix-based system in the desktop computer
Desktop computer
A desktop computer is a personal computer in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Early desktop computers are designed to lay flat on the desk, while modern towers stand upright...
market.
2000s
In 2000, SCO sold its entire UNIX business and assets to Caldera Systems, which later on changed its name to The SCO Group.The bursting of the dot-com bubble
Dot-com bubble
The dot-com bubble was a speculative bubble covering roughly 1995–2000 during which stock markets in industrialized nations saw their equity value rise rapidly from growth in the more...
(2001–2003) led to significant consolidation of versions of Unix. Of the many commercial variants of Unix that were born in the 1980s, only Solaris
Solaris Operating System
Solaris is a Unix operating system originally developed by Sun Microsystems. It superseded their earlier SunOS in 1993. Oracle Solaris, as it is now known, has been owned by Oracle Corporation since Oracle's acquisition of Sun in January 2010....
, HP-UX
HP-UX
HP-UX is Hewlett-Packard's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984...
, and AIX
AIX operating system
AIX AIX AIX (Advanced Interactive eXecutive, pronounced "a i ex" is a series of proprietary Unix operating systems developed and sold by IBM for several of its computer platforms...
were still doing relatively well in the market, though SGI's IRIX
IRIX
IRIX is a computer operating system developed by Silicon Graphics, Inc. to run natively on their 32- and 64-bit MIPS architecture workstations and servers. It was based on UNIX System V with BSD extensions. IRIX was the first operating system to include the XFS file system.The last major version...
persisted for quite some time. Of these, Solaris had the largest market share in 2005.
In 2003, the SCO Group started legal action against various users and vendors of Linux. SCO had alleged that Linux contained copyrighted Unix code now owned by The SCO Group. Other allegations included trade-secret violations by IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
, or contract violations by former Santa Cruz customers who had since converted to Linux. However, Novell disputed the SCO Group's claim to hold copyright on the UNIX source base. According to Novell, SCO (and hence the SCO Group) are effectively franchise operators for Novell, which also retained the core copyrights, veto rights over future licensing activities of SCO, and 95% of the licensing revenue. The SCO Group disagreed with this, and the dispute resulted in the SCO v. Novell
SCO v. Novell
SCO v. Novell was a United States lawsuit in which the The SCO Group claimed ownership of the source code for the Unix operating system, including portions of Linux...
lawsuit. On August 10, 2007, a major portion of the case was decided in Novell's favor (that Novell had the copyright to UNIX, and that the SCO Group had improperly kept money that was due to Novell). The court also ruled that "SCO is obligated to recognize Novell's waiver of SCO's claims against IBM and Sequent". After the ruling, Novell announced they have no interest in suing people over Unix and stated, "We don't believe there is Unix in Linux". SCO successfully got the 10th Circuit Court of Appeals to partially overturn this decision on August 24, 2009 which sent the lawsuit back to the courts for a jury trial.
On March 30, 2010, following a jury trial, Novell, and not The SCO Group, was "unanimously [found]" to be the owner of the UNIX and UnixWare copyrights. The SCO Group, through bankruptcy trustee Edward Cahn, decided to continue the lawsuit against IBM for causing a decline in SCO revenues.
In 2005, Sun Microsystems
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
released the bulk of its Solaris system code (based on UNIX System V
UNIX System V
Unix System V, commonly abbreviated SysV , is one of the first commercial versions of the Unix operating system. It was originally developed by American Telephone & Telegraph and first released in 1983. Four major versions of System V were released, termed Releases 1, 2, 3 and 4...
Release 4) into an open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
project called OpenSolaris
OpenSolaris
OpenSolaris was an open source computer operating system based on Solaris created by Sun Microsystems. It was also the name of the project initiated by Sun to build a developer and user community around the software...
. New Sun OS technologies, notably the ZFS
ZFS
In computing, ZFS is a combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include data integrity verification against data corruption modes , support for high storage capacities, integration of the concepts of filesystem and volume management,...
file system, were first released as open source code via the OpenSolaris project. Soon afterwards, OpenSolaris spawned several non-Sun distributions. In 2010, after Oracle acquired Sun, OpenSolaris was officially discontinued, but the development of derivatives continued.
Standards
Beginning in the late 1980s, an open operating system standardization effort now known as POSIXPOSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
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
Single UNIX Specification
The Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
administered by The Open Group
The Open Group
The Open Group is a vendor and technology-neutral industry consortium, currently with over three hundred member organizations. It was formed in 1996 when X/Open merged with the Open Software Foundation...
. Starting in 1998 the Open Group and IEEE started the Austin Group
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....
, to provide a common definition of POSIX and the Single UNIX Specification.
In an effort towards compatibility, in 1999 several Unix system vendors agreed on SVR4's Executable and Linkable Format
Executable and Linkable Format
In computing, the Executable and Linkable Format is a common standard file format for executables, object code, shared libraries, and core dumps. First published in the System V Application Binary Interface specification, and later in the Tool Interface Standard, it was quickly accepted among...
(ELF) as the standard for binary and object code files. The common format allows substantial binary compatibility among Unix systems operating on the same CPU architecture.
The Filesystem Hierarchy Standard
Filesystem Hierarchy Standard
The Filesystem Hierarchy Standard defines the main directories and their contents in Linux operating systems. For the most part, it is a formalization and extension of the traditional BSD filesystem hierarchy....
was created to provide a reference directory layout for Unix-like operating systems, particularly Linux.
Components
The Unix system is composed of several components that are normally packaged together. By including – in addition to the kernel of an operating system – the development environment, libraries, documents, and the portable, modifiable source-code for all of these components, 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 10MB, and arrived on a single 9-track magnetic tape
Magnetic tape data storage
Magnetic tape data storage uses digital recording on to magnetic tape to store digital information. Modern magnetic tape is most commonly packaged in cartridges and cassettes. The device that performs actual writing or reading of data is a tape drive...
. The printed documentation, typeset from the on-line 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:
- cc – C languageC (programming language)C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
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 system library with C run-time support, was the primary library, but there have always been additional libraries for such things as mathematical functions (libm) 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 – build manager (introduced in PWB/UNIXPWB/UNIXThe Programmer's Workbench was an early version of the Unix operating system created in the Bell Labs Computer Science Research Group of AT&T....
), 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 scripting language, and later versions and implementations contain many other language compilers and toolsets. Early BSD releases included PascalPascal (programming language)Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal...
tools, and many modern Unix systems also include the GNU Compiler CollectionGNU Compiler CollectionThe GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
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), and debugging tools.
- cc – C language
- 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), and more general-purpose applications such as the text formatting and typesetting package. Nonetheless, some major categories are:
- shBourne shellThe Bourne shell, or sh, was the default Unix shell of Unix Version 7 and most Unix-like systems continue to have /bin/sh - which will be the Bourne shell, or a symbolic link or hard link to a compatible shell - even when more modern shells are used by most users.Developed by Stephen Bourne at AT&T...
– The "shell" programmable command line interpreter, the primary user interface on Unix before window systems appeared, and even afterward (within a "command window"). - Utilities – the core tool kit of the Unix command set, including cp, ls, grep, find and many others. Subcategories include:
- System utilities – administrative tools such as mkfsMkfsmkfs is the Linux/GNU command for formatting a disk partition with a specific filesystem.- Syntax :The basic syntax is: mkfs -t type device...
, fsckFsckThe system utility fsck is a tool for checking the consistency of a file system in Unix and Unix-like operating systems such as Linux.-Use:...
, and many others. - User utilities – environment management tools such as passwd, kill, and others.
- System utilities – administrative tools such as mkfs
- Document formatting – Unix systems were used from the outset for document preparation and typesetting systems, and included many related programs such as nroffNroffnroff is a Unix text-formatting program; it produces output suitable for simple fixed-width printers and terminal windows...
, troffTrofftroff is a document processing system developed by AT&T for the Unix operating system.-History:troff can trace its origins back to a text formatting program called RUNOFF, written by Jerome H. Saltzer for MIT's CTSS operating system in the mid-1960s...
, tblTblPart of the troff suite of Unix document layout tools, tbl is a preprocessor that formats tables.Like the main troff program, tbl uses command lines interspersed with data to be printed...
, eqnEqnPart of the troff suite of Unix document layout tools, eqn is a preprocessor that formats equations for printing. A similar program, neqn, accepted the same input as eqn, but produced output tuned to look better in nroff...
, referRefer (software)refer is a program for managing bibliographic references,and citing them in troff documents.It is implemented as a troff preprocessor.refer was written by Mike E...
, and picPic languageIn computing, Pic is a domain-specific programming language by Brian Kernighan for specifying diagrams in terms of objects such as boxes with arrows between them. The pic compiler translates this description into concrete drawing commands. Pic is a procedural programming language, with variable...
. Some modern Unix systems also include packages such as TeXTeXTeX is a typesetting system designed and mostly written by Donald Knuth and released in 1978. Within the typesetting system, its name is formatted as ....
and GhostscriptGhostscriptGhostscript is a suite of software based on an interpreter for Adobe Systems' PostScript and Portable Document Format page description languages.- Features :...
. - 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 as a standard windowing system and GUIGuiGui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
, and many support OpenGLOpenGLOpenGL is a standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. 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 UUCPUUCPUUCP is an abbreviation for 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. Specifically, a command named uucp is one of the programs in the suite; it...
, and systems beginning with BSD release 4.1c included TCP/IP utilities.
- sh
- Documentation – Unix was the first operating system to include all of its documentation online in machine-readable form. The documentation included:
- manManual page (Unix)Man pages are the extensive documentation that comes preinstalled with almost all substantial Unix and Unix-like operating systems. The Unix command used to display them is man. Each page is a self-contained document.- Usage :...
– manual pages for each command, library component, system callSystem callIn computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
, header file, etc. - doc – longer documents detailing major subsystems, such as the C language and troff
- man
Impact
The Unix system had significant impact on other operating systems. It won its success by:- Direct interaction.
- Moving away from the total control of businesses like IBM and DEC.
- AT&T being willing to give the software away for free.
- Running on cheap hardware.
- Being easy to adopt and move to different machines.
It was written in high level language rather than assembly language
Assembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
(which had been thought necessary for systems implementation on early computers). Although this followed the lead of Multics
Multics
Multics was an influential early time-sharing operating system. The project was started in 1964 in Cambridge, Massachusetts...
and Burroughs, 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 printer
Computer printer
In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...
s, terminal
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...
s, or disk drives), providing a uniform interface, but at the expense of occasionally requiring additional mechanisms such as ioctl
Ioctl
In computing, ioctl, short for input/output control, is a system call for device-specific operations and other operations which cannot be expressed by regular system calls. It takes a parameter specifying a request code; the effect of a call depends completely on the request code. Request codes are...
and mode flags to access features of the hardware that did not fit the simple "stream of bytes" model. The Plan 9
Plan 9 from Bell Labs
Plan 9 from Bell Labs is a distributed operating system. It was developed primarily for research purposes as the successor to Unix by the Computing Sciences Research Center at Bell Labs between the mid-1980s and 2002...
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-11
RSX-11
RSX-11 is a family of real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation , common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972...
M's "group, user" hierarchy evolved into VMS directories, CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
's volumes evolved into MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
2.0+ subdirectories, and HP's MPE
Multi-Programming Executive
MPE is a business-oriented minicomputer operating system made by Hewlett-Packard.It runs the HP 3000 family of computers, which originally used HP custom 16 bit stack architecture CISC CPUs and were later migrated to PA-RISC where the operating system was called MPE/XL...
group.account hierarchy and IBM's SSP
System Support Program
System Support Program was an operating system for the IBM System/34 and System/36 minicomputers. SSP was a command-based operating system released in 1977, the days of CP/M, DOS, and the original UNIX.- History :...
and OS/400
OS/400
IBM i is an EBCDIC based operating system that runs on IBM Power Systems. It is the current evolution of the operating system named i5/OS which was originally named OS/400 when it was introduced with the AS/400 computer system in 1988....
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
Unix shell
A Unix shell is a command-line interpreter or shell that provides a traditional user interface for the Unix operating system and for Unix-like systems...
used the same language for interactive commands as for scripting (shell script
Shell script
A shell script is a script written for the shell, or command line interpreter, of an operating system. It is often considered a simple domain-specific programming language...
s – there was no separate job control language like IBM's JCL
Job Control Language
Job Control Language is a scripting language used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem....
). Since the shell and OS commands were "just another program", the user could choose (or even write) his 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
Pipeline (Unix)
In Unix-like computer operating systems , a pipeline is the original software pipeline: a set of processes chained by their standard streams, so that the output of each process feeds directly as input to the next one. Each connection is implemented by an anonymous pipe...
) made a powerful programming paradigm (coroutine
Coroutine
Coroutines are computer program components that generalize subroutines to allow multiple entry points for suspending and resuming execution at certain locations...
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 ASCII 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
Record-oriented filesystem
In computer science, a record-oriented filesystem is a file system where files are stored as collections of records. There are several different record formats; the details vary depending on the particular system...
. 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
PostScript
PostScript is a dynamically typed concatenative programming language created by John Warnock and Charles Geschke in 1982. It is best known for its use as a page description language in the electronic and desktop publishing areas. Adobe PostScript 3 is also the worldwide printing and imaging...
, ODF
ODF
ODF may be an acronym for:* OpenDocument format, a standard for electronic office documents** OpenDocument Fellowship, a volunteer organisation with members around the world to promote the use and development of the OpenDocument format....
), and at the application layer of the Internet protocols
Internet protocol suite
The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...
, e.g., FTP, SMTP, HTTP, SOAP
SOAP
SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks...
and SIP
Session Initiation Protocol
The Session Initiation Protocol is an IETF-defined signaling protocol widely used for controlling communication sessions such as voice and video calls over Internet Protocol . The protocol can be used for creating, modifying and terminating two-party or multiparty sessions...
.
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
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
soon spread beyond Unix, and is now ubiquitous in systems and applications programming.
Early Unix developers were important in bringing the concepts of modularity
Modularity (programming)
Modular programming is a software design technique that increases the extent to which software is composed of separate, interchangeable components called modules by breaking down program functions into modules, each of which accomplishes one function and contains everything necessary to accomplish...
and reusability
Reusability
In computer science and software engineering, reusability is the likelihood a segment of source code that can be used again to add new functionalities with slight or no modification...
into software engineering
Software engineering
Software Engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software, and the study of these approaches; that is, the application of engineering to software...
practice, spawning a "software tools" movement.
Unix provided the TCP/IP networking protocol on relatively inexpensive computers, which contributed to the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
explosion of worldwide real-time connectivity, and which formed the basis for implementations on many other platforms. This also exposed numerous security holes in the networking implementations.
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 1983 launch of the free software movement
Free software movement
The free software movement is a social and political movement with the goal of ensuring software users' four basic freedoms: the freedom to run their software, to study and change their software, and to redistribute copies with or without changes. The alternative terms "software libre", "open...
.
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
Unix philosophy
The Unix philosophy is a set of cultural norms and philosophical approaches to developing software based on the experience of leading developers of the Unix operating system.-McIlroy: A Quarter Century of Unix:...
.
Free Unix-like operating systems
In 1983, Richard StallmanRichard Stallman
Richard Matthew Stallman , often shortened to rms,"'Richard Stallman' is just my mundane name; you can call me 'rms'"|last= Stallman|first= Richard|date= N.D.|work=Richard Stallman's homepage...
announced the GNU
GNU
GNU is a Unix-like computer operating system developed by the GNU project, ultimately aiming to be a "complete Unix-compatible software system"...
project, an ambitious effort to create a free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
Unix-like
Unix-like
A Unix-like 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....
system; "free" in 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
GNU Hurd
GNU Hurd is a free software Unix-like replacement for the Unix kernel, released under the GNU General Public License. It has been under development since 1990 by the GNU Project of the Free Software Foundation...
, had not produced a working kernel, but in 1991 Linus Torvalds
Linus Torvalds
Linus Benedict Torvalds is a Finnish software engineer and hacker, best known for having initiated the development of the open source Linux kernel. He later became the chief architect of the Linux kernel, and now acts as the project's coordinator...
released the Linux kernel
Linux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
as free software under the GNU General Public License
GNU General Public License
The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
. In addition to their use in the GNU/Linux operating system, many GNU packages – such as the GNU Compiler Collection
GNU Compiler Collection
The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
(and the rest of the GNU toolchain
GNU toolchain
The GNU toolchain is a blanket term for a collection of programming tools produced by the GNU Project. These tools form a toolchain used for developing applications and operating systems....
), the GNU C library and the GNU core utilities – have gone on to play central roles in other free Unix systems as well.
Linux distributions, comprising Linux and large collections of compatible software have become popular both with individual users and in business. Popular distributions include Red Hat Enterprise Linux
Red Hat Enterprise Linux
Red Hat Enterprise Linux is a Linux-based operating system developed by Red Hat and targeted toward the commercial market. Red Hat Enterprise Linux is released in server versions for x86, x86-64, Itanium, PowerPC and IBM System z, and desktop versions for x86 and x86-64...
, Fedora
Fedora (operating system)
Fedora is a RPM-based, general purpose collection of software, including an operating system based on the Linux kernel, developed by the community-supported Fedora Project and sponsored by Red Hat...
, SUSE Linux Enterprise, openSUSE
OpenSUSE
openSUSE is a general purpose operating system built on top of the Linux kernel, developed by the community-supported openSUSE Project and sponsored by SUSE...
, Debian GNU/Linux
Debian
Debian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...
, Ubuntu
Ubuntu (operating system)
Ubuntu is a computer operating system based on the Debian Linux distribution and distributed as free and open source software. It is named after the Southern African philosophy of Ubuntu...
, Mandriva Linux
Mandriva Linux
Mandriva Linux is a Linux distribution distributed by Mandriva. It uses the RPM Package Manager...
, Slackware Linux and Gentoo
Gentoo Linux
Gentoo Linux is a computer operating system built on top of the Linux kernel and based on the Portage package management system. It is distributed as free and open source software. Unlike a conventional software distribution, the user compiles the source code locally according to their chosen...
.
A free derivative of BSD Unix, 386BSD
386BSD
386BSD, sometimes called "Jolix", was a free Unix-like operating system based on BSD, first released in 1992. It ran on PC compatible computer systems based on the Intel 80386 microprocessor...
, was also released in 1992 and led to the NetBSD
NetBSD
NetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...
and FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
projects. With the 1994 settlement of a lawsuit that UNIX Systems Laboratories brought against the University of California and Berkeley Software Design Inc. (USL v. BSDi
USL v. BSDi
USL v. BSDi was a lawsuit brought in the United States in 1992 by Unix System Laboratories against Berkeley Software Design, Inc and the Regents of the University of California over intellectual property related to UNIX...
), 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 directions, including OpenBSD
OpenBSD
OpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
and DragonFly BSD
DragonFly BSD
DragonFly BSD is a free Unix-like operating system created as a fork of FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and a FreeBSD developer between 1994 and 2003, began work on DragonFly BSD in June 2003 and announced it on the FreeBSD mailing lists on July...
.
Linux and BSD are now rapidly occupying much of the market traditionally occupied by proprietary Unix operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. Due to the modularity of the Unix design, sharing bits and pieces is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and modern systems also usually include some GNU utilities in their distributions.
OpenSolaris
OpenSolaris
OpenSolaris was an open source computer operating system based on Solaris created by Sun Microsystems. It was also the name of the project initiated by Sun to build a developer and user community around the software...
is a relatively recent addition to the list of operating systems based on free software licenses marked as such by FSF
Free Software Foundation
The Free Software Foundation is a non-profit corporation founded by Richard Stallman on 4 October 1985 to support the free software movement, a copyleft-based movement which aims to promote the universal freedom to create, distribute and modify computer software...
and OSI
Open Source Initiative
The Open Source Initiative is an organization dedicated to promoting open source software.The organization was founded in February 1998, by Bruce Perens and Eric S. Raymond, prompted by Netscape Communications Corporation publishing the source code for its flagship Netscape Communicator product...
. It includes a number of derivatives that combines CDDL-licensed kernel and system tools and also GNU
GNU
GNU is a Unix-like computer operating system developed by the GNU project, ultimately aiming to be a "complete Unix-compatible software system"...
userland and is currently the only open source System V derivative available.
2038
Unix stores system time values as the number of seconds from midnight January 1, 1970 (the "Unix Epoch") in variables of typetime t, historically defined as "signed long". On January 19, 2038 on 32 bit Unix systems, the current time will roll over from a zero followed by 31 ones (0x7FFFFFFF) to a one followed by 31 zeros (0x80000000), which will reset time to the year 1901 or 1970, depending on implementation, because that toggles the sign bitSign bit
In computer science, the sign bit is a bit in a computer numbering format that indicates the sign of a number. In IEEE format, the sign bit is the leftmost bit...
.
Since times before 1970 are rarely represented in Unix time
Unix time
Unix time, or POSIX time, is a system for describing instants in time, defined as the number of seconds elapsed since midnight Coordinated Universal Time of Thursday, January 1, 1970 , not counting leap seconds, which are declared by the International Earth Rotation and Reference Systems Service...
, one possible solution that is compatible with existing binary formats would be to redefine
time_t as "unsigned 32-bit integer". However, such a kludgeKludge
A kludge is a workaround, a quick-and-dirty solution, a clumsy or inelegant, yet effective, solution to a problem, typically using parts that are cobbled together...
merely postpones the problem to February 7, 2106, and could introduce bugs in software that computes time differences.
Some Unix versions have already addressed this. For example, in Solaris and Linux in 64-bit mode,
time_t is 64 bits long, meaning that the OS itself and 64-bit applications will correctly handle dates for some 292 billion years. Existing 32-bit applications using a 32-bit time_t continue to work on 64-bit Solaris systems but are still prone to the 2038 problem. Some vendors have introduced an alternative 64-bit type and corresponding API, without addressing uses of the standard time_t.ARPANET
In May 1975 ARPA documented in RFC 681 detailed very specifically why Unix was the operating system of choice for use as an ARPANETARPANET
The Advanced Research Projects Agency Network , was the world's first operational packet switching network and the core network of a set that came to compose the global Internet...
mini-host. The evaluation process was also documented. Unix required a license that was very expensive with $20,000(US) for non-university
University
A university is an institution of higher education and research, which grants academic degrees in a variety of subjects. A university is an organisation that provides both undergraduate education and postgraduate education...
users and $150 for an educational license. It was noted that for an ARPA network-wide license Bell "were open to suggestions in that area".
Specific features found beneficial were:
- Local processing facilities.
- CompilerCompilerA compiler is a computer program that transforms source code written in a programming language into another computer language...
s. - EditorText editorA text editor is a type of program used for editing plain text files.Text editors are often provided with operating systems or software development packages, and can be used to change configuration files and programming language source code....
. - Document preparation systemRoffroff was the first Unix text-formatting computer program, the most important application run on the first machine specifically purchased to run UNIX, and a predecessor of the nroff and troff document processing systems....
. - Efficient file system and access control.
- MountableMount (computing)Mounting takes place before a computer can use any kind of storage device . The user or their operating system must make it accessible through the computer's file system. A user can access only files on mounted media.- Mount point :A mount point is a physical location in the partition used as a...
and de-mountable volumes. - Unified treatment of peripherals as special filesDevice file systemIn Unix-like operating systems, a device file or special file is an interface for a device driver that appears in a file system as if it were an ordinary file. There are also special device files in MS-DOS and Microsoft Windows...
. - The network control programNetwork Control ProgramThe Network Control Program provided the middle layers of the protocol stack running on host computers of the ARPANET, the predecessor to the modern Internet...
(NCP) was integrated within the Unix file system. - Network connectionsConnection-oriented protocolA connection-oriented networking protocol is one that establishes a communication session, then delivers a stream of data in the same order as it was sent. It may be a circuit switched connection, or a virtual circuit connection in a packet switched network...
treated as special files which can be accessed through standard Unix I/O callsSystem callIn computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
. - The system closes all files on program exit.
- "desirable to minimize the amount of code added to the basic Unix kernel".
Branding
In October 1993, NovellNovell
Novell, Inc. is a multinational software and services company. It is a wholly owned subsidiary of The Attachmate Group. It specializes in network operating systems, such as Novell NetWare; systems management solutions, such as Novell ZENworks; and collaboration solutions, such as Novell Groupwise...
, the company that owned the rights to the Unix System V source at the time, transferred the trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
s of Unix to the X/Open Company (now The Open Group
The Open Group
The Open Group is a vendor and technology-neutral industry consortium, currently with over three hundred member organizations. It was formed in 1996 when X/Open merged with the Open Software Foundation...
), and in 1995 sold the related business operations to Santa Cruz Operation. Whether Novell also sold the copyright
Copyright
Copyright is a legal concept, enacted by most governments, giving the creator of an original work exclusive rights to it, usually for a limited time...
s to the actual software was the subject of a 2006 federal lawsuit, SCO v. Novell
SCO v. Novell
SCO v. Novell was a United States lawsuit in which the The SCO Group claimed ownership of the source code for the Unix operating system, including portions of Linux...
, which Novell won. The case was appealed, but on Aug 30, 2011, the United States Court of Appeals for the Tenth Circuit affirmed the trial decisions, closing the case. Unix vendor SCO Group Inc.
SCO Group
TSG Group, Inc. is a software company formerly called The SCO Group, Caldera Systems, and Caldera International. After acquiring the Santa Cruz Operation's Server Software and Services divisions, as well as UnixWare and OpenServer technologies, the company changed its focus to UNIX...
accused Novell of slander of title
Slander of title
In law, slander of title is normally a claim involving real estate in which one entity falsely claims to own another entity's property. Alternatively, it is casting aspersion on someone else's property, business or goods, e.g. claiming a house is infested with termites , or falsely claiming you own...
.
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
Single UNIX Specification
The Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
qualify as "UNIX" (others are called "Unix system-like" or "Unix-like
Unix-like
A Unix-like 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....
").
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 fee to The Open Group. Systems licensed to use the UNIX trademark include AIX, HP-UX
HP-UX
HP-UX is Hewlett-Packard's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984...
, IRIX
IRIX
IRIX is a computer operating system developed by Silicon Graphics, Inc. to run natively on their 32- and 64-bit MIPS architecture workstations and servers. It was based on UNIX System V with BSD extensions. IRIX was the first operating system to include the XFS file system.The last major version...
, Solaris, Tru64 (formerly "Digital UNIX"), A/UX
A/UX
A/UX was Apple Computer’s implementation of the Unix operating system for some of their Macintosh computers. The later versions of A/UX ran on the Macintosh II, Quadra and Centris series of machines as well as the SE/30. A/UX was first released in 1988, with the final version released in 1995...
, Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, and a part of z/OS
Z/OS
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
.
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, e.g. Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, BSD, etc., 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
Genericized trademark
A genericized trademark is a trademark or brand name that has become the colloquial or generic description for, or synonymous with, a general class of product or service, rather than as an indicator of source or affiliation as intended by the trademark's holder...
.
"Unix" was the original formatting, but the usage of "U "font-variant:small-caps">NIX" remains widespread because, according to Dennis Ritchie
Dennis Ritchie
Dennis MacAlistair Ritchie , was an American computer scientist who "helped shape the digital era." He created the C programming language and, with long-time colleague Ken Thompson, the UNIX operating system...
, when presenting the original Unix paper to the third Operating Systems Symposium of the American Association for Computing Machinery
Association for Computing Machinery
The Association for Computing Machinery is a learned society for computing. It was founded in 1947 as the world's first scientific and educational computing society. Its membership is more than 92,000 as of 2009...
, “we had a new typesetter and troff
Troff
troff is a document processing system developed by AT&T for the Unix operating system.-History:troff can trace its origins back to a text formatting program called RUNOFF, written by Jerome H. Saltzer for MIT's CTSS operating system in the mid-1960s...
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.
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
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
noun of the third declension, is also popular. The pseudo-Anglo-Saxon plural form Unixen is not common, although occasionally seen. 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 book shelves, ink pens, bottled glue, diapers, hair driers and food containers.
See also
- Comparison of operating systemsComparison of operating systemsThese tables compare general and technical information for a number of widely used and currently available operating systems.Because of the large number and variety of available Linux distributions, they are all grouped under a single entry; see comparison of Linux distributions for a detailed...
- Comparison of open source and closed source
- Hungarian Unix PortalHungarian Unix PortalSince 2000 the Hungarian Unix Portal , founded by Gabor Micsko aka. trey, is the largest Hungarian UNIX/Linux/BSD system administrators' webpage. On this page you can read news, get help in the forum, discuss the news, etc....
- List of operating systems
- List of Unix utilities
- List of Unix systems
- Market share of operating systems
- Operating systems timelineOperating systems timelineThis article presents a timeline of events in the history of computer operating systems from 1951 to the current day. For a narrative explaining the overall developments, see the History of operating systems.-1950s:* 1951...
- Plan 9 from Bell LabsPlan 9 from Bell LabsPlan 9 from Bell Labs is a distributed operating system. It was developed primarily for research purposes as the successor to Unix by the Computing Sciences Research Center at Bell Labs between the mid-1980s and 2002...
Further reading
Books- Salus, Peter H.Peter H. SalusPeter H. Salus is a linguist, computer scientist, historian of technology, author in many fields, and an editor of books and journals. He has conducted research in germanistics, language acquisition, and computer languages...
: A Quarter Century of UNIX, Addison Wesley, June 1, 1994; ISBN 0-201-54777-5
Television
- Computer ChroniclesComputer ChroniclesThe Computer Chronicles was a US television series, broadcast during 1981-2002 on Public Broadcasting Service public television, which documented the rise of the personal computer from its infancy to the immense market at the turn of the century...
(1985). "UNIX". - Computer ChroniclesComputer ChroniclesThe Computer Chronicles was a US television series, broadcast during 1981-2002 on Public Broadcasting Service public television, which documented the rise of the personal computer from its infancy to the immense market at the turn of the century...
(1989). "Unix".
External links
- The UNIX System, at The Open GroupThe Open GroupThe Open Group is a vendor and technology-neutral industry consortium, currently with over three hundred member organizations. It was formed in 1996 when X/Open merged with the Open Software Foundation...
. - The Evolution of the Unix Time-sharing System
- The Creation of the UNIX Operating System
- The Unix Tree: files from historic releases
- The Unix and Linux Forums
- UNIXhelp for users
- The Unix 1st Edition Manuals.