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.
, 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.
Overview
Introduction
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
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.
Releases
SVR1
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.
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 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.
Maurice J. Bach's book, The Design of the UNIX Operating System, is the definitive description of the SVR2 kernel.