View source for UNIX System V

{{Short description|Early commercial UNIX operating system}}
{{Redirect|System 5|the Mac OS version|Classic Mac OS#System Software 5}}
{{Redirect|SysV|the Init|Init#SysV-style}}
{{Distinguish|Version 5 Unix}}
{{Use American English|date = April 2019}}
{{Infobox OS
| name = Unix System V
| logo = 
| screenshot = [[File:HP-HP9000-715-100-Workstation_03.jpg|frameless]]
| caption = [[HP 9000]] workstation booting [[HP-UX]], [[Hewlett-Packard]]'s System V
| developer = [[AT&T Corporation]]
| family = [[Unix]]
| working state = Historic
| source model = [[Closed source]] except for [[OpenSolaris]] and its derivatives
| released = {{Start date and age|1983}}<ref>{{cite web|url=https://unix.org/Posters/download/unix_posterA3_Screen.pdf|title=The Single UNIX® Specification History & Timeline|website=unix.org|date=2004}}</ref>
| discontinued = <!-- DON'T use this for articles about releases of operating systems -->
| RTM date = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} ONLY for articles about OS releases -->
| GA date = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} ONLY for articles about OS releases -->
| latest release version = 
| latest release date = 
| latest preview version = 
| latest preview date = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} -->
| marketing target = 
| programmed in = [[C (programming language)|C]]
| language = [[English language|English]]<!-- Supported human languages (English, French, Italian, Arabic, ...) -->
| update model = <!-- APT, Windows Update, etc. -->
| package manager = <!-- dpkg, rpm, Windows installer, etc. -->
| supported platforms = <!-- IA-32, x64, Itanium, ARM, etc. -->
| kernel type = <!-- Hybrid, Monolithic, Microkernel, Exokernel, Nanokernel, etc. -->
| userland = 
| ui = [[Command-line interface]]
| license = 
| preceded by = [[UNIX System III]]
| succeeded by = [[UnixWare]]
| website = <!-- {{URL|www.example.org}} -->
| support status = <!-- For articles about releases of operating systems ONLY -->
| other articles = 
}}
'''Unix System V''' (pronounced: "System Five") is one of the first commercial versions of the [[Unix]] [[operating system]]. It was originally developed by [[AT&T Corporation|AT&T]] and first released in 1983. Four major versions of System V were released, numbered 1, 2, 3, and 4. System V Release 4 (SVR4) was commercially the most successful version, being the result of an effort, marketed as ''Unix System Unification'', which solicited the collaboration of the major Unix vendors. It was the source of several common commercial Unix features. System V is sometimes abbreviated to '''SysV'''.

{{As of|2021}}, the AT&T-derived Unix market is divided between four System V variants: [[IBM]]'s [[IBM AIX|AIX]], [[Hewlett Packard Enterprise]]'s [[HP-UX]] and [[Oracle Corporation|Oracle]]'s [[Solaris (operating system)|Solaris]],<ref name="lastdays">{{cite web |url=https://www.networkworld.com/article/677972/servers-the-last-days-of-unix.html |title=The Last Days of Unix |author=Julie Sartain |website=Network World |date=19 August 2013 |access-date=9 January 2024}}</ref> plus the free-software [[illumos]] forked from [[OpenSolaris]].

== Overview ==

=== Introduction ===
[[File:Unix history-simple.svg|thumb|Unix history tree]]
[[File:ATT UNIX System V License Plate.jpeg|thumb|[[AT&T]] System V [[license plate]] ]]
[[File:SVR1-PDP11.png|alt=UNIX System V Release 1 on SIMH (PDP-11)|thumb|UNIX System V Release 1 on SIMH (PDP-11)]]
System V was the successor to 1982's [[UNIX System III]]. While AT&T developed and sold hardware that ran System V, most customers ran a version from a reseller, based on AT&T's [[reference implementation]]. A standards document called the [[System V Interface Definition]] outlined the default features and behavior of implementations.

=== AT&T support ===
During the formative years of AT&T's computer business, the division went through several phases of System V software groups, beginning with the Unix Support Group (USG), followed by Unix System Development Laboratory (USDL), followed by AT&T Information Systems (ATTIS), and finally [[Unix System Laboratories]] (USL).

=== Rivalry with BSD ===
{{Main|Unix wars}}
In the 1980s and early-1990s, UNIX System V and the [[Berkeley Software Distribution]] (BSD) were the two major versions of UNIX. Historically, BSD was also commonly called "BSD Unix" or "Berkeley Unix".<ref>Garfinkel, Simson. Spafford, Gene. Schwartz, Alan. ''Practical UNIX and Internet Security.'' 2003. pp. 15-20</ref> [[Eric S. Raymond]] summarizes the longstanding relationship and rivalry between System V and BSD during the early period:<ref>Raymond, Eric S. ''The Art of Unix Programming.'' 2003. p. 38</ref>

{{quote|In fact, for years after divestiture the Unix community was preoccupied with the first phase of the [[Unix wars]]&nbsp;– an internal dispute, the rivalry between System V Unix and BSD Unix. The dispute had several levels, some technical ([[Berkeley sockets|sockets]] vs. [[STREAMS|streams]], BSD tty vs. System V termio) and some cultural. The divide was roughly between longhairs and shorthairs; [[programmer]]s and technical people tended to line up with Berkeley and BSD, more business-oriented types with AT&T and System V.}}

While HP, IBM and others chose System V as the basis for their Unix offerings, other vendors such as [[Sun Microsystems]] and [[Digital Equipment Corporation|DEC]] extended BSD. Throughout its development, though, System V was infused with features from BSD, while BSD variants such as DEC's [[Ultrix]] received System V features. AT&T and Sun Microsystems worked together to merge System V with BSD-based [[SunOS]] to produce [[Solaris (operating system)|Solaris]], one of the primary System V descendants still in use today{{When|date=December 2019}}. Since the early 1990s, due to standardization efforts such as [[POSIX]] and the success of [[Linux]], the division between System V and BSD has become less important.

== Releases ==
[[File:Teletype_DMD_5620.jpg|thumb|DMD 5620 terminal, based on the [[Blit (computer terminal)|''Blit'']], connected to a SVR3 host and showing the ''Layers'' interface]]

=== SVR1 ===
System V, known inside Bell Labs as Unix 5.0, succeeded AT&T's previous commercial Unix called [[UNIX System III|System III]] in January, 1983.<ref name="levenez">{{cite web
| url         = http://www.levenez.com/unix/
| title       = Unix History (Unix Timeline)
| first       = Éric
| last        = Lévénez
| archive-url  = https://web.archive.org/web/20020802080343/http://www.levenez.com/unix/
| archive-date = 2002-08-02
| url-status    = live
| access-date  = 2010-12-29
}}</ref>
Unix 4.0 was never released externally, which would have been designated as System IV.<ref>{{cite book |title=Overview of the XENIX 286 Operating System |publisher=Intel Corporation |date= November 1984 |url=http://bitsavers.trailing-edge.com/pdf/intel/system3xx/xenix-286/174385-001_Overview_of_the_XENIX_286_Operating_System_Nov84.pdf |page=1.10 |quote=There was no System IV.}}</ref><ref>{{cite newsgroup
  | title = UNIX History
  | author = Dale Dejager
  | date = 1984-01-16
  | newsgroup = net.unix
  | url = http://groups.google.com/group/net.unix/msg/b80689d4b3bff13f?dmode=source
}}</ref><ref>{{cite book |title=Modern Operating Systems |last=Tanenbaum |first=Andrew S. |quote=Whatever happened to System IV is one of the great unsolved mysteries of computer science. |location=Upper Saddle River, NJ |publisher=Prentice Hall |edition=2nd |year=2001 |page=[https://archive.org/details/modernoperatings00tane/page/675 675] |isbn=0-13-031358-0 |url=https://archive.org/details/modernoperatings00tane/page/675 }}</ref>
This first release of System V (called System V.0, System V Release 1, or SVR1) was developed by AT&T's UNIX Support Group (USG) and based on the Bell Labs internal USG UNIX 5.0.

System V also included features such as the [[Vi (text editor)|vi]] editor and [[curses (programming library)|curses]] from 4.1 BSD, developed at the [[University of California, Berkeley]]; it also improved performance by adding buffer and [[inode]] caches. It also added support for [[inter-process communication]] using messages, [[semaphore (programming)|semaphore]]s, and [[shared memory (interprocess communication)|shared memory]], developed earlier for the Bell-internal [[CB UNIX]].<ref name="kerrisk">{{cite book |title=The Linux Programming Interface |last=Kerrisk |first=Michael |year=2010 |publisher=No Starch Press |page=921}}</ref>

SVR1 ran on [[Digital Equipment Corporation|DEC]] [[PDP-11]] and [[VAX]] [[minicomputer]]s.

=== SVR2 ===
[[File:VAX 11-780 intero.jpg|thumb|The [[Digital Equipment Corporation|DEC]] [[VAX-11/780]] was the porting base for SVR2.]]

AT&T's UNIX Support Group (USG) transformed into the UNIX System Development Laboratory (USDL), which released System V Release 2 in 1984. SVR2 added [[Unix shell|shell]] functions and the [[System V Interface Definition|SVID]]. SVR2.4 added [[demand paging]], [[copy-on-write]], [[shared memory]], and record and [[file locking]].

The concept of the "porting base" was formalized, and the DEC [[VAX-11/780]] was chosen for this release. The "porting base" is the so-called original version of a release, from which all porting efforts for other machines emanate.

Educational source licenses for SVR2 were offered by AT&T for US$800 for the first CPU, and $400 for each additional CPU. A commercial source license was offered for $43,000, with three months of support, and a $16,000 price per additional CPU.<ref>{{cite web |title=UNIX System V and add on applications prices |url=https://www.bell-labs.com/usr/dmr/www/licenses/pricelist84.pdf |publisher=AT&T International |date=24 February 1983 |access-date=24 January 2024}}</ref>

[[Apple Computer]]'s [[A/UX]] operating system was initially based on this release. [[Xenix|SCO XENIX]] also used SVR2 as its basis. The first release of [[HP-UX]] was also an SVR2 derivative.<ref name="Rosen"/>{{rp|33}}

Maurice J. Bach's book, ''The Design of the UNIX Operating System'', is the definitive description of the SVR2 kernel.<ref>{{Citation
|last=Bach
|first=Maurice
|title=The Design of the UNIX Operating System
|publisher=Prentice Hall
|year=1986
|bibcode=1986duos.book.....B
|isbn=0-13-201799-7
|url=https://archive.org/details/designofunixoper00bach
}}</ref>

=== SVR3 ===
[[Image:3B2_model_400_sitting_on_grass.jpg|thumb|The AT&T [[3B series computers#3B2|3B2]] line of [[minicomputer]]s was the porting base for SVR3.]]

AT&T's UNIX System Development Laboratory (USDL) was succeeded by AT&T Information Systems (ATTIS), which distributed UNIX System V, Release 3, in 1987.<ref>{{citation | author=Marshall Kirk McKusick | author-link=Marshall Kirk McKusick | chapter=History of the UNIX System | title=The Design and Implementation of the FreeBSD Operating System | edition=2nd | year=2015 | pages=23–28}}</ref> SVR3 included [[STREAMS]], [[Remote File Sharing]] (RFS), the File System Switch (FSS) [[virtual file system]] mechanism, a restricted form of [[shared library|shared libraries]], and the [[Transport Layer Interface]] (TLI) network [[application programming interface|API]]. The final version was Release 3.2 in 1988, which added binary compatibility to [[Xenix]] on Intel platforms (see [[Intel Binary Compatibility Standard]]).

User interface improvements included the "layers" windowing system for the [[Blit (computer terminal)|DMD 5620]] graphics terminal, and the SVR3.2 [[curses (programming library)|curses libraries]] that offered eight or more color pairs and other at this time important features (forms, panels, menus, etc.). The [[3B series computers#3B2|AT&T 3B2]] became the official "porting base."

[[SCO UNIX]] was based upon SVR3.2, as was [[Interactive Systems Corporation|ISC]] [[Interactive Unix|386/ix]]. Among the more obscure distributions of SVR3.2 for the 386 were ESIX 3.2 by [[Everex]] and "System V, Release 3.2" sold by Intel themselves; these two shipped "plain vanilla" AT&T's codebase.<ref name="IW1989">{{cite journal|author=Jeff Tye|title=Other OSs That Run Unix on a 386|url=https://books.google.com/books?id=ijAEAAAAMBAJ&pg=PT77|date=10 July 1989|journal=InfoWorld|pages=62|issn=0199-6649}}</ref>

[[IBM]]'s [[AIX operating system]] is an SVR3 derivative.

=== SVR4 === <!-- This section is linked from [[SVR4]] -->
[[File:HP-HP9000-C110-Workstation 10.jpg|thumb|[[HP 9000]] C110 running [[HP-UX]] in console mode]]
[[File:Openwindows.jpg|thumb|[[OpenWindows]], an early [[desktop environment]] for SVR4]]
[[File:HP-HP9000-735-99-Workstation 02.jpg|thumb|[[HP 9000]] 735 running [[HP-UX]] with the [[Common Desktop Environment]] (CDE)]]
[[File:Unix SVR4.2 mousepad.jpg|thumb|'Catch the wave' promotional mousepad for SVR4.2]]
[[File:Sun Ultra 20 Workstation (2005).jpeg|thumb|[[Sun Ultra series|Sun Ultra 20]] with [[Solaris (operating system)|Solaris]] 10]]

System V Release 4.0 was announced on October 18, 1988<ref>{{cite press release
 |title=  SEVERAL MAJOR COMPUTER AND SOFTWARE COMPANIES ANNOUNCE STRATEGIC COMMITMENT TO AT&T'S UNIX SYSTEM V, RELEASE 4.0
 |publisher= Amdahl, Control Data Corporation, et al.
 |date= October 18, 1988
 |url= http://groups.google.com/group/comp.unix.questions/msg/2e02a599c5c62848
 |access-date= 2007-01-01
  }}</ref> and was incorporated into a variety of commercial Unix products from early 1989 onwards.<ref name="levenez"/>  A joint project of AT&T Unix System Laboratories and [[Sun Microsystems]],<ref name="patton19880118">{{Cite magazine |last=Patton |first=Carole |date=18 January 1988 |title=Sun and AT&T Plan to Engineer Next-Generation Unix System 
 |url=https://books.google.com/books?id=Dz8EAAAAMBAJ&pg=PA11#v=onepage&q&f=false |access-date=2025-05-25 |magazine=[[InfoWorld]] |page=11 |volume=10 |issue=3}}</ref> it combined technology from:

* SVR3
* [[Berkeley Software Distribution|4.3BSD]]
* [[Xenix]]
* [[SunOS]]

New features included:

* From BSD:
** [[TCP/IP]] support
** Sockets
** [[Unix File System|UFS]]
** Support for multiple groups
** [[C shell]]
* From SunOS:
** [[Virtual file system]] interface (replacing File System Switch in System V Release 3)
** [[Network File System (protocol)|NFS]]
** New virtual memory system including support for [[mmap|memory mapped]] files
** Improved shared library system based on the SunOS 4.x model<ref name="Levine_1999_CH10"/>
** [[OpenWindows]] [[GUI]] environment
** [[External Data Representation]] (XDR) and [[ONC RPC]]
* From Xenix:
** x86 [[device driver]]s
** Binary compatibility with Xenix (in the x86 version of System V)
* [[KornShell]]
* [[C (programming language)#ANSI C and ISO C|ANSI X3J11 C]] compatibility
* Multi-National Language Support (MNLS)
* Better [[internationalization and localization|internationalization]] support
* An [[application binary interface]] (ABI) based on [[Executable and Linkable Format]] (ELF)
* Support for standards such as [[POSIX]] and [[X/Open]]

Many companies licensed SVR4 and bundled it with computer systems such as [[workstation]]s and [[network server]]s. SVR4 systems vendors included [[Atari Corporation|Atari]] ([[Atari System V]]), [[Commodore International|Commodore]] ([[Amiga Unix]]), [[Data General]] ([[DG/UX]]), [[Fujitsu]] ([[UXP/DS]]), [[Hitachi]] (HI-UX), Hewlett-Packard (HP-UX), [[NCR Corporation|NCR]] ([[Unix/NS]]), [[NEC]] ([[EWS-UX]], UP-UX, UX/4800, [[SUPER-UX]]), [[Oki Electric Industry|OKI]] (OKI System V), [[Pyramid Technology]] ([[DC/OSx]]), [[Silicon Graphics|SGI]] ([[IRIX]]), [[Siemens]] ([[SINIX]]), [[Sony]] ([[Sony NEWS|NEWS-OS]]), [[Sumitomo Electric Industries]] (SEIUX), and [[Sun Microsystems]] ([[Solaris (operating system)|Solaris]]) with [[illumos]] in the 2010s as the only [[open-source software|open-source]] platform.

Software porting houses also sold enhanced and supported [[x86 architecture|Intel x86]] versions. SVR4 software vendors included [[Dell]] (Dell UNIX),<ref>{{Citation
 |title=Technologists notes&nbsp;— A brief history of Dell UNIX
 |url=http://technologists.com/notes/2008/01/10/a-brief-history-of-dell-unix/
 |date=10 January 2008
 |access-date=2009-02-18
}}</ref> [[Everex]] (ESIX), Micro Station Technology (SVR4), [[Microport Systems|Microport]] (SVR4), and UHC (SVR4).<ref>[[Eric S. Raymond]], [http://www.catb.org/~esr/faqs/clone-unix-guide.txt A buyer's guide to UNIX versions for PC-clone hardware], posted to [[Usenet]] November 16, 1994.</ref>

The primary platforms for SVR4 were Intel x86 and [[SPARC]]; the SPARC version, called Solaris 2 (or, internally, [[SunOS]] 5.x), was developed by Sun. The relationship between Sun and AT&T was terminated after the release of SVR4, meaning that later versions of Solaris did not inherit features of later SVR4.x releases. Sun would in 2005 release most of the source code for Solaris 10 (SunOS 5.10) as the [[open-source software|open-source]] [[OpenSolaris]] project, creating, with its forks, the only open-source (albeit heavily modified) System V implementation available. After [[Oracle Corporation|Oracle]] took over Sun, Solaris was [[Fork (software development)|fork]]ed into proprietary release, but [[illumos]] as the continuation project is being developed in open-source.

A consortium of Intel-based resellers including [[Unisys]], [[International Computers Limited|ICL]], [[NCR Corporation]], and [[Olivetti]] developed SVR4.0MP with [[multiprocessing]] capability (allowing system calls to be processed from any processor, but interrupt servicing only from a "master" processor).<ref>
{{Citation
 |title=Unix Internatl. and USL release early version of SVR4 multiprocessing software
 |url=http://www.allbusiness.com/technology/computer-software/165194-1.html
 |date=17 June 1991
 |archive-url=https://web.archive.org/web/20100111232743/https://www.allbusiness.com/technology/computer-software/165194-1.html
 |archive-date=2010-01-11
 |access-date=2009-04-22
}}
</ref>

Release 4.1 ES (Enhanced Security) added security features required for [[Trusted Computer System Evaluation Criteria|Orange Book]] B2 compliance and [[Access Control List]]s and support for dynamic loading of kernel modules.<ref>{{cite journal |title=Unix International reviews the Unix System V.4 story so far |author=William Fellows |date=13 August 1992 |journal=Computer Business Review |url=http://www.cbronline.com/news/unix_international_reviews_the_unix_system_v4_story_so_far |access-date=2008-10-31 |archive-url=https://web.archive.org/web/20090221065610/http://www.cbronline.com/news/unix_international_reviews_the_unix_system_v4_story_so_far |archive-date=2009-02-21}}</ref><ref>
{{Citation
 |title=Computer Security
 |first=Matt
 |last=Bishop
 |publisher=Addison Wesley
 |date=December 2, 2002
 |isbn=0-201-44099-7
 |page=505
}}
</ref>

=== SVR4.2 / UnixWare ===
In 1992, AT&T USL engaged in a joint venture with [[Novell]], called [[Univel]]. That year saw the release System V.4.2 as Univel [[UnixWare]], featuring the [[Veritas File System]]. Other vendors included UHC and Consensys. Release 4.2MP, completed late 1993, added support for multiprocessing and it was released as UnixWare 2 in 1995.<ref>{{Citation
 |url=http://www.novell.com/news/press/archive/1995/03/pr00026.html
 |title=UnixWare 2 Product Announcement Questions& Answers
 |year=1995
}}</ref>

Eric S. Raymond warned prospective buyers about SVR4.2 versions, as they often did not include on-line [[man pages]]. In his 1994 buyers guide, he attributes this change in policy to Unix System Laboratories.<ref>{{cite web|url=http://www.catb.org/~esr/faqs/clone-unix-guide.txt|title=PC-clone UNIX Software Buyer's Guide|author=Eric S. Raymond|date=16 November 1994|access-date=6 May 2014}}</ref>

=== SVR5 / UnixWare 7 ===
The [[Santa Cruz Operation]] (SCO), owners of Xenix, eventually acquired the UnixWare trademark and the distribution rights to the System V Release 4.2 codebase from Novell, while other vendors (Sun, IBM, HP) continued to use and extend System V Release 4. Novell transferred ownership of the Unix trademark to [[The Open Group]]. 

System V Release 5 was developed in 1997 by the [[Santa Cruz Operation]] (SCO) as a merger of [[SCO OpenServer]] (an SVR3-derivative) and UnixWare, with a focus on large-scale servers.<ref name="Rosen">{{cite book |author=Kenneth H. Rosen |year=1999 |title=UNIX: The Complete Reference |publisher=McGraw-Hill Professional}}</ref>{{rp|23,32}} It was released as SCO UnixWare 7. SCO's successor, [[The SCO Group]], also based [[SCO OpenServer]] 6 on SVR5, but the codebase is not used by any other major developer or reseller.

=== SVR6 (cancelled) ===
System V Release 6 was announced by SCO to be released by the end of 2004, but was apparently cancelled.<ref>{{cite web|url=http://www.infoworld.com/t/platforms/sco-updates-unix-openserver-product-plans-798 |title=SCO updates Unix, OpenServer product plans |website=InfoWorld |date=August 19, 2003 |author=Deni Connor}}</ref> It was supposed to support 64-bit systems.<ref>[https://archive.today/20120722095807/http://website.scobenelux.com/roadmap.php SCO UNIX Roadmap at Archive.is]</ref> SCO also introduced Smallfoot in 2004, a low-resource "embeddable" variant of UnixWare for dedicated commercial and industrial applications, in an attempt that was perceived as a response to the growing popularity of Linux.<ref name="sdtimes20040615_smallfoot">{{ cite magazine | url=https://archive.org/details/sdtimes106/page/n24/mode/1up | title=SCO Steps Into Embedded Market With Smallfoot | magazine=Software Development Times | last1=Correia | first1=Edward J. | date=15 June 2004 | access-date=24 May 2024 | issue=106 | pages=25 }}</ref> The industry has since coalesced around [[The Open Group]]'s Single UNIX Specification version 3 ([[Single UNIX Specification|UNIX 03]]).

== Market position ==

=== Availability during the 1990s on x86 platforms ===
[[File:OpenSolaris 2009.06 screenshot.png|thumb|A [[GNOME]]-based [[OpenSolaris]] desktop, OpenSolaris was one of the SVR4 varieties available for x86 platforms]]
In the 1980s and 1990s, a variety of SVR4 versions of Unix were available commercially for the x86 PC platform. However, the market for commercial Unix on PCs declined after [[Linux]] and BSD became widely available. In late 1994, [[Eric S. Raymond]] discontinued his ''PC-clone UNIX Software Buyer's Guide'' on [[USENET]], stating, "The reason I am dropping this is that I run Linux now, and I no longer find the SVr4 market interesting or significant."<ref>{{cite web|url=http://www.catb.org/~esr/faqs/clone-unix-guide.txt|title=PC-clone UNIX Software Buyer's Guide|author=Eric S. Raymond|date=16 November 1994|access-date=3 February 2014}}</ref>

In 1998, a [[Halloween Documents|confidential memo]] at Microsoft stated, "Linux is on track to eventually own the x86 UNIX market", and further predicted, "I believe that Linux&nbsp;– moreso than [[Windows NT|NT]]&nbsp;– will be the biggest threat to SCO in the near future."<ref>{{cite web|url=http://www.catb.org/~esr/halloween/halloween1.html|title=Open Source Software: A (New?) Development Methodology|author=Vinod Valloppillil|date=11 August 1998|access-date=3 February 2014}}</ref>

An ''[[InfoWorld]]'' article from 2001 characterized SCO UnixWare as having a "bleak outlook" due to being "trounced" in the market by Linux and Solaris, and IDC predicted that SCO would "continue to see a shrinking share of the market".<ref name="2001_vital_signs">{{cite news|url=http://www.computerworld.com/article/2584450/operating-systems/vital-signs-for-unix.html|title=Vital Signs for Unix|author=Tom Yager|newspaper=[[Computerworld]]|date=19 November 2001|access-date=5 June 2015}}</ref>

=== Project Monterey ===
[[Project Monterey]] was started in 1998 to combine major features of existing commercial Unix platforms, as a joint project of [[Compaq]], IBM, Intel, SCO, and [[Sequent Computer Systems]]. The target platform was meant to be Intel's new [[IA-64]] architecture and [[Itanium]] line of processors. However, the project was abruptly canceled in 2001 after little progress.<ref>Raymond, Eric S. ''The Art of Unix Programming.'' 2003. p. 43</ref>

=== System V and the Unix market ===
By 2001, several major Unix variants such as SCO UnixWare, Compaq [[Tru64 UNIX]], and SGI IRIX were all in decline.<ref name="2001_vital_signs"/> The three major Unix versions doing well in the market were IBM AIX, Hewlett-Packard's HP-UX, and Sun's Solaris.<ref name="2001_vital_signs"/>

In 2006, when SGI declared bankruptcy, analysts questioned whether Linux would replace proprietary Unix altogether. In a 2006 article written for ''[[Computerworld]]'' by Mark Hall, the economics of Linux were cited as a major factor driving the migration from Unix to Linux:<ref name="2006_end_of_unix">{{citation|url=http://www.computerworld.com/article/2555262/operating-systems/the-end-of-unix-.html|title=The End of Unix?|author=Mark Hall|date=15 May 2006|access-date=5 June 2015}}</ref>

{{quote|Linux's success in high-end, [[scientific computing|scientific]] and [[high-performance technical computing|technical computing]], like Unix's before it, preceded its success in your [[data center]]. Once Linux proved itself by executing the most complex calculations possible, IT managers quickly grasped that it could easily [[web server|serve Web pages]] and run [[payroll]]. Naturally, it helps to be lucky: Free, downloadable Linux's star began to rise during one of the longest downturns in IT history. With companies doing more with less, one thing they could dump was Unix.}}

The article also cites trends in high-performance computing applications as evidence of a dramatic shift from Unix to Linux:<ref name="2006_end_of_unix"/>

{{quote|A look at the [[TOP500|Top500]] list of [[supercomputer]]s tells the tale best. In 1998, Unix machines from Sun and SGI combined for 46% of the 500 fastest computers in the world. Linux accounted for one (0.2%). In 2005, Sun had 0.8%&nbsp;— or four systems&nbsp;— and SGI had 3.6%, while 72% of the Top500 ran Linux.}}

In a November 2015 survey of the top 500 supercomputers, Unix was used by only 1.2% (all running IBM AIX), while Linux was used by 98.8%; the same survey in November 2017 reports 100% of them using Linux.<ref name="top500_stats">{{cite web|url=http://www.top500.org/statistics/list/|title=TOP500 Supercomputer Sites - List Statistics|access-date=28 January 2016}}</ref>

System V derivatives continued to be deployed on some proprietary server platforms. The principal variants of System V that remain in commercial use are AIX (IBM), Solaris (Oracle), and HP-UX (HP). According to a study done by [[International Data Corporation|IDC]], in 2012 the worldwide Unix market was divided between IBM (56%), Oracle (19.2%), and HP (18.6%). No other commercial Unix vendor had more than 2% of the market.{{r|lastdays}} Industry analysts generally characterize proprietary Unix as having entered a period of slow but permanent decline.<ref>{{cite web|url=http://www.computerworld.com/article/2486806/linux/as-unix-fades-away-from-data-centers--it-s-unclear-what-s-next.html|title=As Unix fades away from data centers, it's unclear what's next|author=Patrick Thibodeau|date=12 December 2013|access-date=6 June 2015|archive-url=https://web.archive.org/web/20150520013205/http://www.computerworld.com/article/2486806/linux/as-unix-fades-away-from-data-centers--it-s-unclear-what-s-next.html|archive-date=2015-05-20}}</ref>

=== OpenSolaris and illumos distributions===
[[File:OpenIndiana Hipster 2021.10 MATE desktop environment screenshot.png|thumb|The [[MATE (desktop environment)|MATE]] desktop on [[OpenIndiana]], an SVR4 derivative]]
OpenSolaris and its derivatives are the only SVR4 descendants that are [[open-source software]]. 
Core system software continues to be developed as [[illumos]], which is used in [[Illumos#Distributions|illumos distributions]] such as [[SmartOS]], [[OpenIndiana]] and others.

=== System V compatibility ===
The System V interprocess communication mechanisms are available in Unix-like operating systems not derived from System V; in particular, in Linux<ref name="kerrisk"/><ref>{{man|7|svipc|Linux}}</ref> (a reimplementation of Unix) as well as the BSD derivative [[FreeBSD]].<ref>{{man|2|msgsnd|FreeBSD}}</ref> POSIX 2008 specifies a replacement for these interfaces.<ref name="kerrisk"/>

FreeBSD maintains a binary compatibility layer for the [[COFF]] format, which allows FreeBSD to execute binaries compiled for some SVR3.2 derivatives such as SCO UNIX and Interactive UNIX.<ref>Lehey, Greg. ''The Complete FreeBSD: Documentation from the Source.'' 2003. pp. 164-165</ref> Modern System V, Linux, and BSD platforms use the [[Executable and Linkable Format|ELF]] file format for natively compiled binaries.

== References ==
{{Reflist|refs=
<ref name="Levine_1999_CH10">{{cite book |author-last=Levine |author-first=John R. |author-link=John R. Levine |title=Linkers and Loaders |date=2000 |orig-year=October 1999 |edition=1 |publisher=[[Morgan Kaufmann]] |series=The Morgan Kaufmann Series in Software Engineering and Programming |location=San Francisco, USA |isbn=1-55860-496-0 |oclc=42413382 |chapter=Chapter 10: Dynamic Linking and Loading |chapter-url=http://www.iecc.com/linker/linker10.html |access-date=2020-01-12 |url-status=dead |archive-url=https://archive.today/20130126045626/http://www.iecc.com/linker/linker10.html |archive-date=2013-01-26}} Code: [https://archive.today/20200114225034/https://linker.iecc.com/code.html]. </ref>
}}

== External links ==
* [http://www.catb.org/~esr/faqs/clone-unix-guide.txt PC-clone UNIX Software Buyer's Guide] by [[Eric S. Raymond]] (posted to [[USENET]] in 1994)
* [http://www.faqs.org/faqs/unix-faq/faq/part6/ Unix FAQ - history]

{{Bell Unix}}
{{Unix-like}}

{{Authority control}}

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[[Category:UNIX System V| ]]
[[Category:Unix distributions]]
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[[Category:1983 software]]