ESIX
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| Developer | AT&T Corporation |
|---|---|
| OS family | Unix |
| Working state | Historic |
| Source model | Closed source |
| Initial release | 1983 |
| Official website | www |
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, 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. System V is sometimes abbreviated to SysV.
As of 2012[update], the Unix market is divided between four System V variants: IBM's AIX, Hewlett-Packard's HP-UX, Oracle's Solaris. and illumos distributions being the open-source OpenSolaris continuation.
System V was the successor to 1982's UNIX System III. While AT&T sold their own hardware that ran System V, most customers instead 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 its formative years, AT&T 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, System V was considered one of the two major versions of UNIX, the other being the Berkeley Software Distribution (BSD). 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:
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