Тұңғыш коммерциялық UNIX жүйесі: System V

Early commercial UNIX operating system

Unix System V (pronounced: "System Five") is one of the first commercial versions of the Unix operating system. It was originally developed by AT&T and first released in 1983. Four major versions of System V were released, numbered 1, 2, 3, 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 AIX, Hewlett Packard Enterprise's HP UX and Oracle's Solaris, plus the free software illumos forked from OpenSolaris.

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.

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).

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". Eric S. Raymond summarizes the longstanding relationship and rivalry between System V and BSD during the early period:

While HP, IBM and others chose System V as the basis for their Unix offerings, other vendors such as Sun Microsystems and 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, one of the primary System V descendants still in use today. 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.

System V, known inside Bell Labs as Unix 5.0, succeeded AT&T's previous commercial Unix called System III in January, 1983. Unix 4.0 was never released externally, which would have been designated as System IV. 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 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, semaphores, and shared memory, developed earlier for the Bell internal CB UNIX. SVR1 ran on DEC PDP 11 and VAX minicomputers.

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 shell functions and the 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. Apple Computer's A/UX operating system was initially based on this release. SCO XENIX also used SVR2 as its basis. The first release of HP UX was also an SVR2 derivative.

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. SVR3 included STREAMS, Remote File Sharing (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 (see Intel Binary Compatibility Standard). 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." SCO UNIX was based upon SVR3.2, as was ISC 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. IBM's AIX operating system is an SVR3 derivative.

System V Release 4.0 was announced on October 18, 1988 and was incorporated into a variety of commercial Unix products from early 1989 onwards. Everex (ESIX), Micro Station Technology (SVR4), Microport (SVR4), and UHC (SVR4). 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, with its forks, the only open source (albeit heavily modified) System V implementation available. After Oracle took over Sun, Solaris was forked into proprietary release, but illumos as the continuation project is being developed in open source. 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). 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.

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. 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.

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. 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. It was supposed to support 64 bit systems. SCO also discontinued Smallfoot in 2004. The industry has coalesced around The Open Group's Single UNIX Specification version 3 (UNIX 03).

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." 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." 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".

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.

OpenSolaris and its derivatives are the only SVR4 descendants that are open source software. Core system software continues to be developed as illumos used in illumos distributions such as SmartOS, Omniosce, OpenIndiana and others.

The System V interprocess communication mechanisms are available in Unix like operating systems not derived from System V; in particular, in Linux (a reimplementation of Unix) as well as the BSD derivative FreeBSD. POSIX 2008 specifies a replacement for these interfaces. Modern System V, Linux, and BSD platforms use the ELF file format for natively compiled binaries.