UNIX System V

From Wikipedia, the free encyclopedia
  (Redirected from System V)
Jump to: navigation, search
UNIX System V
Company / developer AT&T Corporation
OS family Unix
Working state Historic
Source model Closed source

UNIX System V, commonly abbreviated SysV (and usually pronounced—though rarely written—as "System Five"), is one of the first commercial versions of the Unix operating system. It was originally developed by American Telephone & Telegraph (AT&T) and first released in 1983. Four major versions of System V were released, termed Releases 1, 2, 3 and 4. System V Release 4, or 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.

While AT&T sold their own hardware that ran System V (see AT&T Computer Systems), 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. The most widely used versions of System V today are IBM's AIX, based on System V Release 3, and Sun's Solaris and Hewlett-Packard's HP-UX, both based on System V Release 4.

In the 1980s and early-1990s, System V was considered one of the two major "flavors" of UNIX, the other being Berkeley Unix (BSD). During the period of the Unix wars System V was known for being the primary choice of manufacturers of large multiuser systems, in opposition to BSD's dominance of desktop workstations.[citation needed] However, with standardization efforts such as POSIX and the commercial success of Linux, this generalization is not as accurate as it once was.

Unix history tree



System V, known inside Bell Labs as Unix 5.0, succeeded AT&T's previous commercial Unix called System III in January, 1983.[1] There was never an external release of Unix 4.0, which would have been System IV.[2][3][4] 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 editor and curses from release 4.1 of the Berkeley Software Distribution of UNIX developed at the University of California, Berkeley (UCB); it also improved performance by adding buffer and inode caches. System V ran on the DEC VAX and PDP-11 machines. It also added support for inter-process communication using messages, semaphores, and shared memory, developed earlier for the Bell-internal CB UNIX.[5]


System V Release 2 was released in April, 1984.[1] It added shell functions and the SVID. New kernel features included record and file locking, demand paging, and copy on write.[6] The concept of the "porting base" was formalized, and the DEC VAX 11/780 was named for this Release. The "porting base" is the so-called original version of a Release, from which all porting efforts for other machines emanate. Maurice J. Bach's The Design of the UNIX Operating System[7] is the definitive description of the System V Release 2 kernel.

Apple Computer's A/UX operating system was initially based on this release. The first release of HP-UX was also an SVR2 derivative.[8]:33


IBM RS/6000 H70 Enterprise Server, an AIX server system (SVR3 derivative)

System V Release 3 was released in 1986.[1][9] It included STREAMS, the Remote File System (RFS), the File System Switch (FSS) virtual file system mechanism, a restricted form of shared libraries, and the Transport Layer Interface (TLI) network API. The final version was Release 3.2 in 1988, which added binary compatibility to Xenix on Intel platforms; SCO OpenServer was based upon 3.2, as was Interactive Systems Corporation (ISC) 386/ix. Among the more obscure (re)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.[10]

User interface improvements included the "layers" windowing system for the DMD 5620 graphics terminal, and the SVR3.2 curses libraries that offered eight or more color pairs and other at this time important features (forms, panels, menus, etc.). The AT&T 3B2 became the official "porting base". IBM's AIX operating system is an SVR3 derivative.


HP HP9000 model 715, booting HP-UX, an SVR4 derivative
The GNOME desktop on OpenSolaris, an SVR4 derivative

System V Release 4.0 was announced on October 18, 1988[11] and was incorporated into a variety of commercial Unix products from early 1989 onwards.[1] A joint project of Unix System Laboratories and Sun Microsystems, it combined technology from Release 3 as well as 4.3BSD, Xenix, and SunOS. New features included:

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 OpenSolaris project, creating the only open-source (heavily modified) System V implementation available. The "Principal Publisher" for SVR4 on the Intel platform was ISC.

Many versions of SVR4 appeared, because of hardware vendors (HP, SGI, NEC, Sony, OKI, Fujitsu) adapting it to their platform, and because porting houses (SCO, Microport, ESIX, UHC)[12] sold enhanced and supported x86 versions. SVR4 was even ported to the Amiga as Amiga Unix and to the Atari TT030 as Atari System V. Other popular SysV derivatives include Dell SVR4[13] and Bull SVR4.

A consortium of Intel based resellers including Unisys, 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).[14] Release 4.1 ES (Enhanced Security) added security features required for Orange Book B2 compliance and Access Control Lists and support for dynamic loading of kernel modules.[15][16]

SVR4.2 / UnixWare[edit]

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.[17]


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. Any operating system that meets the Single Unix Specification (SUS), effectively a successor to the System V Interface Definition, may be granted Unix rights. The SUS is met by Apple's Mac OS X, a BSD derivative, as well as several other operating systems not derived from either BSD or System V.

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.[8]: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.


System V Release 6 was announced by SCO to be released by the end of 2004, but was apparently cancelled.[18] It was supposed to support 64-bit systems.[19]

Real-time derivatives[edit]

Some operating systems derived from System V but used a RTOS-flavored kernel. Among these are NEC's RX-UX832 and some versions of Venix.


Decline on x86 platforms[edit]

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 went into slow decline 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."[20] In 1998, a confidential memo at Microsoft stated, "Linux is on track to eventually own the x86 UNIX market," and further predicted, "I believe that Linux – moreso than NT – will be the biggest threat to SCO in the near future."[21]

Proprietary server platforms[edit]

The principal System V derivatives that remain in commercial use are AIX, HP-UX, and Solaris.

OpenSolaris and Illumos[edit]

OpenSolaris and its derivatives are currently the only SVR4 descendants that are open-source software. Core system software continues to be developed as Illumos.

System V compatibility[edit]

The System V interprocess communication mechanisms are even available in Unix-like operating systems not derived from System V; in particular, in Linux[5][22] (a reimplementation of Unix) as well as the BSD derivative FreeBSD.[23] POSIX 2008 specifies a replacement for these interfaces.[5]


  1. ^ a b c d Lévénez, Éric. "Unix History (Unix Timeline)". Archived from the original on 2010-12-29. Retrieved 2010-12-29. 
  2. ^ Overview of the XENIX 286 Operating System. Intel Corporation. November 1984. p. 1.10. "There was no System IV." 
  3. ^ Dale Dejager (1984-01-16). "UNIX History". net.unix. Web link.
  4. ^ Tanenbaum, Andrew S. (2001). Modern Operating Systems (2nd ed.). Upper Saddle River, NJ: Prentice Hall. p. 675. ISBN 0-13-031358-0. "Whatever happened to System IV is one of the great unsolved mysteries of computer science." 
  5. ^ a b c Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 921. 
  6. ^ Goodheart, Berny; James Cox (1994), The Magic Garden Explained, Prentice Hall, p. 11, ISBN 0-13-098138-9 
  7. ^ Bach, Maurice (1986), The Design of the UNIX Operating System, Prentice Hall, ISBN 0-13-201799-7 
  8. ^ a b Kenneth H. Rosen (1999). UNIX: The Complete Reference. McGraw-Hill Professional. 
  9. ^ Rargo, Stephan A. (April 10, 1993), UNIX System V Network Programming, Addison-Wesley Professional, ISBN 978-0-201-56318-4 
  10. ^ Jeff Tye (10 July 1989). Other OSs That Run Unix on a 386. InfoWorld. p. 62. ISSN 01996649. 
  11. ^ "SEVERAL MAJOR COMPUTER AND SOFTWARE COMPANIES ANNOUNCE STRATEGIC COMMITMENT TO AT&T'S UNIX SYSTEM V, RELEASE 4.0" (Press release). Amdahl, Control Data Corporation, et al. October 18, 1988. Retrieved 2007-01-01. 
  12. ^ Eric S. Raymond, A buyer's guide to UNIX versions for PC-clone hardware, posted to Usenet November 16, 1994.
  13. ^ Technologists notes — A brief history of Dell UNIX, 10 January 2008, retrieved 2009-02-18 
  14. ^ Unix Internatl. and USL release early version of SVR4 multiprocessing software, 17 June 1991, retrieved 2009-04-22 
  15. ^ William Fellows (13 August 1992). "Unix International reviews the Unix System V.4 story so far". Computer Business Review. Retrieved 2008-10-31. 
  16. ^ Bishop, Matt (December 2, 2002), Computer Security, Addison Wesley, p. 505, ISBN 0-201-44099-7 
  17. ^ UnixWare 2 Product Announcement Questions& Answers, 1995 
  18. ^ SCO updates Unix, OpenServer product plans InfoWorld, August 19, 2003
  19. ^ SCO UNIX Roadmap at Archive.is
  20. ^ Eric S. Raymond (16 November 1994). "PC-clone UNIX Software Buyer's Guide". Retrieved 3 February 2014. 
  21. ^ Vinod Valloppillil (11 August 1998). "Open Source Software: A (New?) Development Methodology". Retrieved 3 February 2014. 
  22. ^ svipc(7) – Linux Programmer's Manual – Overview, Conventions and Miscellanea
  23. ^ msgsnd(2) – FreeBSD System Calls Manual

External links[edit]