Unix

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Unix
Evolution of Unix and Unix-like systems
Company / developer	Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna & Bell Labs
Programmed in	C
OS family	Unix
Working state	Active
Source model	Historically closed source, now some Unix projects (BSD family and Illumos) are open sourced.
Initial release	1969
Available language(s)	English
Available programming languages(s)	C, C++
Kernel type	Monolithic
Default user interface	Command-line interface & Graphical (X Window System)
License	Proprietary
Official website	unix.org

Unix (officially trademarked as UNIX, sometimes also written as 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 systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations. The second edition of Unix was released on December 6th, 1972.
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" (though the Open Group disapproves of this term).^[1] 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. Today, in addition to certified Unix systems such as those already mentioned, Unix-like operating systems such as MINIX, Linux 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.

[hide]

[edit] Overview

Unix operating systems are widely used in servers, workstations, and mobile devices.^[2] 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.
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 tools, small programs that can be strung together through a command line interpreter using pipes, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are collectively known as the Unix philosophy.
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, perhaps most importantly, schedules access to hardware to avoid conflicts if two programs try to access the same resource or device simultaneously. To mediate such access, the kernel was given special rights on the system, leading to 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 "normal" 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, and in the 1980s non-blocking I/O and the set of inter-process communication mechanisms was augmented (sockets, shared memory, message queues, semaphores), and functionalities such as network protocols were moved out of the kernel.

[edit] History

In the 1960s, Massachusetts Institute of Technology, AT&T Bell Labs, and General Electric developed an experimental operating system called Multics for the GE-645 mainframe.^[3] 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,^[4] 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."^[4]
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.^[5] On this PDP7, 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.^[4]

[edit] 1970s

In the 1970s Brian Kernighan coined the project name Unics as a play 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", made up 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".^[6] 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 nontelephone 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”.^[7]
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.^[8]
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.

[edit] 1980s

A Unix desktop running the X Window System graphical user interface. Shown are a number of client applications common to the MIT X Consortium's distribution, including Tom's Window Manager, an X Terminal, Xbiff, xload, and a graphical manual page browser.

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.
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 1956 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.^[7] The Free Software Foundation (FSF) 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.^[9] 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.

[edit] 1990s

In 1990, the Open Software Foundation 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 runs on IBM PC clones.
By 1993 most commercial vendors had changed their variants of Unix to be based on System V with many BSD features added on top. The creation of the 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 that year. By that time the only vendor using it was Digital, 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 to the Biblical story of Esau selling his birthright for the proverbial "mess of pottage".^[10]) Novell developed its own version, UnixWare, merging its NetWare with UNIX System V Release 4. Novell tried to use this to battle 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.^[11] 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.^[12] 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.

[edit] 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 (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.^[13]
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".^[14]^[15]^[16] 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.^[17]^[18]^[19]
On March 30, 2010, following a jury trial, Novell, and not The SCO Group, is "unanimously [found]" to be the owner of the UNIX and UnixWare copyrights.^[20] The SCO Group, through bankruptcy trustee Edward Cahn, has decided to continue the lawsuit against IBM for causing a decline in SCO revenues.^[21]

[edit] Standards

Beginning in the late 1980s, an open operating system standardization effort now known as POSIX provided a common baseline for all operating systems; IEEE based POSIX around the common structure of the major competing variants of the Unix system, publishing the first POSIX standard in 1988. In the early 1990s a separate but very similar effort was started by an industry consortium, the Common Open Software Environment (COSE) initiative, which eventually became the Single UNIX Specification 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.

[edit] Components

[edit] Impact

[edit] Free Unix-like operating systems

In 1983, Richard Stallman 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.

[edit] 2038

Main article: Year 2038 problem

Unix stores system time values as the number of seconds from midnight January 1, 1970 (the "Unix Epoch") in variables of type time_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 bit.
Since times before 1970 are rarely represented in Unix time, one possible solution that is compatible with existing binary formats would be to redefine time_t as "unsigned 32-bit integer". However, such a kludge 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.

[edit] ARPANET

In May 1975 ARPA documented in RFC 681 detailed very specifically why Unix was the operating system of choice for use as an ARPANET "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:

Local processing facilities.
Compilers.
Editor.
Document preparation system.
Efficient file system and access control.
Mountable and de-mountable volumes.
Unified treatment of peripherals as special files.
The network control program (NCP) was integrated within the Unix file system.
Network connections treated as special files which can be accessed through standard Unix I/O calls.
The system closes all files on program exit.
"desirable to minimize the amount of code added to the basic Unix kernel".

[edit] Branding

[edit] See also

	Book: Unix
Wikipedia Books are collections of articles that can be downloaded or ordered in print.

[edit] References

^ Unix.org
^ 8:30 AM (2010-09-29). "Unix’s Revenge". asymco. Retrieved 2010-11-09.
^ Stuart, Brian L. (2009). Principles of operating systems: design & applications. Boston, Massachusetts: Thompson Learning. p. 23. ISBN 1-4188-3769-5.
^ ^a ^b ^c Ritchie, Dennis M.. "The Evolution of the Unix Time-sharing System". Retrieved 2009-11-29.
^ "The Creation of the UNIX* Operating System: The famous PDP-7 comes to the rescue". Bell-labs.com. Retrieved 2010-11-09.
^ Stallings, William. "Operating Systems: Internals and Design Principles" 5th ed, page 91. Pearson Education, Inc. 2005.
^ ^a ^b "Origins and History of Unix, 1969–1995". Faqs.org. Retrieved 2010-11-09.
^ D. E. Bodenstab, T. F. Houghton, K. A. Kelleman, G. Ronkin, and E. P. Schan (October 1984). "UNIX Operating System Porting Experiences" (PDF). AT&T Bell Laboratories Technical Journal, Vol. 63, No. 8 Part 2. p. 9. Retrieved 2009-04-09.
^ "UNIX". The Computer Chronicles. 1985.
^ "comp.unix.questions | Google Groups". Groups.google.com. Retrieved 2010-11-09.
^ ^a ^b Chuck Karish View profile More options. "The name "UNIX" is now the property of X/Open – comp.std.unix | Google Groups". Groups.google.com. Retrieved 2010-11-09.
^ ^a ^b "HP, Novell and SCO To Deliver High-Volume UNIX OS With Advanced Network And Enterprise Services". Novell.com. 1995-09-20. Retrieved 2010-11-09.
^ Stephen Shankland (December 7, 2005). "Itanium: A cautionary tale". Tech News. ZDNet. Archived from the original on 2006-09-23. Retrieved 2006-10-04. "In the third quarter of this year, 7,845 Itanium servers were sold, according to research by Gartner. That compares with 62,776 machines with Sun Microsystems' UltraSparc, 31,648 with IBM's Power, and 9,147 with HP's PA-RISC."
^ "Memorandum and Decision Order in SCO v. Novell". Groklaw.net. Retrieved 2010-11-09.
^ Tuxrocks.com
^ Novell Won't Pursue Unix Copyrights August 15, 2007
^ Groklaw.net August 24, 2009
^ Novell.com August 24, 2009
^ Wired.com August 24, 2009
^ "03/30/2010 – 846 – JURY VERDICT for Defendant Novell. (slm) (Entered: 03/30/2010)" (PDF). Retrieved 2010-11-09.
^ Jury says Novell owns Unix copyrights
^ Jones, Pamela. "SCO Files Docketing Statement and We Find Out What Its Appeal Will Be About". Groklaw. Groklaw.net. Retrieved 12 April 2011.
^ The Open Group. "Mac OS X v10.5 Leopard on Intel-based Macintosh computers certification". Retrieved 2007-06-12.
^ The Open Group. "Mac OS X v10.6 Snow Leopard certification".
^ "Unix". Catb.org. Retrieved 2010-11-09.
^ "Autres Unix, autres moeurs (OtherUnix)". Cm.bell-labs.com. 2000-04-01. Retrieved 2010-11-09.

Ritchie, D.M.; Thompson, K., The UNIX Time-Sharing System (The Bell System Technical Journal, July–August 1978, Vol. 57, No. 6, Part 2)
"UNIX History". www.levenez.com. Retrieved 17 March 2005.
"AIX, FreeBSD, HP-UX, Linux, Solaris, Tru64". UNIXguide.net. Retrieved 17 March 2005.
"Linux Weekly News, February 21, 2002". lwn.net. Retrieved 7 April 2006.
Lions, John: Lions' "Commentary on the Sixth Edition UNIX Operating System". with Source Code, Peer-to-Peer Communications, 1996; ISBN 1-57398-013-7
UNIX Shell Programming, Yashawant Kanetkar

[edit] Further reading

Books

Salus, Peter H.: A Quarter Century of UNIX, Addison Wesley, June 1, 1994; ISBN 0-201-54777-5

Television

Computer Chronicles (1985). "UNIX".
Computer Chronicles (1989). "Unix".

[edit] External links

The Wikibook Guide to Unix has a page on the topic of

Commands

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Sunday, May 22, 2011

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Unix

Contents

[edit] Overview

[edit] History

[edit] 1970s

[edit] 1980s

[edit] 1990s

[edit] 2000s

[edit] Standards

[edit] Components

[edit] Impact

[edit] Free Unix-like operating systems

[edit] 2038

[edit] ARPANET

[edit] Branding

[edit] See also

[edit] References

[edit] Further reading

[edit] External links

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