page_title: UNIX System V
section_title: Introduction
hierarchical_section_title: UNIX System V / Overview / Introduction
caption_attribution_description: English: AT&amp;T UNIX System V license plate, displayed in Japan.
context_page_description: Unix System V 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 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 2020, the AT&T-derived Unix market is divided between three System V variants: IBM's AIX, Hewlett-Packard's HP-UX and Oracle's Solaris.
context_section_description: 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.
caption: AT&T System V license plate
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