UNIX is a family of operating systems that derive from the original AT&T UNIX, developed in the 1970s at the Bell Labs research center by Ken Thompson and Dennis Ritchie.

Currently, the UNIX trademark passed to the industry standards consortium The Open Group, which allows the use of the mark for certified operating systems compliant with the Single UNIX Specification.

Portable Operating System Interface (POSIX)

POSIX is a family of standards specified by the IEEE for maintaining compatibility between operating systems.

POSIX defines the API, command line shells and utility interfaces.

The name POSIX was coined by Richard Stallman the founder of the Free Software Foundation.

• 1988 - First publication, IEEE 1003.1-1988.
• 1990 - Update, IEEE 1003.1-1990.
• 1990 - Adopted by ISO, published as ISO/IEC 9945-1:1990 (POSIX.1).
• 1996 - Update, 1003.1-1996, inclusion of threads. Also published as ISO/IEC 9945:1996.
• 1999 - POSIX revision, 1003.1d-1999. More real-time interfaces.
• 2000 - Update 1003.1j-2000 and 1003.1q-2000.
• 2001 - New major version, IEEE 1003.1-2001. Also known as POSIX:2001. Merges several standards: combined the various 1003.1 publications and portions of the Single UNIX Specification
• 2004 - Update, IEEE 1003.1-2004. Also known as POSIX:2004.
• 2008 - Update, IEEE 1003.1-2008. Also known as POSIX:2008.
• 2009 - ISO/IEC 9945:2009 based on the new POSIX.1 specification.

Single UNIX Specification (SUS)

SUS is a superset of the POSIX.1 standard. Also sets some POSIX optional interface groups as mandatory. Was a publication of The Open Group, founded in 1996 as a merge of X/Open and The Open Software Foundation. Actually is maintained by the Austin Group.

The specification became more popular because it was available at no cost, whereas the IEEE charged a substantial fee for access the POSIX specification.

• 1994 - First release by the X/Open group (Spec 1170).
• 1996 - The Open Group was formed.
• 1997 - Version 2.
• 2001 - Version 3. That is a merge of the SUS and the POSIX specification. Also known as POSIX:2001 (1003.1-2001).
• 2008 - Version 4.

C Language

The origin of the language is closely tied to the development of UNIX.

Originally implemented in assembly language on a PDP-7 by Dennis Ritchie and Ken Thompson and used in the re-implementation of the research UNIX.

• 1972 - First appearance in version 2 UNIX.
• 1989 - Standard was approved, ANSI X3.159-1989.
• 1990 - ANSI standard was adopted by ISO/IEC 9899:1990.
• 1999 - ISO update, ISO/IEC 9899:1999.
• 2011 - ISS update, ISO/IEC 9899:2011

UNIX Systems

• 1969 - a team of Bell Labs researchers lead by Thompson and Ritchie developed on a PDP-7 computer the first operating system destined to become Unix.
• 1970 - Peter G. Neumann coined the project name Unics.
• 1973 - Unix is rewritten in C and ported to a PDP-11.

AT&T System V

Originally developed by AT&T. Four major versions of System V were released numbered 1, 2, 3, and 4. The release 4 (SVR4) was the most successful version, being the result of an effort marked as “UNIX System Unification”.

The System V Interface definition (SVID) is a standard that describes the System V behavior, including system calls, C libraries, available programs and devices.

• 1975 - First AT&T system release (System I)
• 1982 - System V
• 1983 - Release 1 (SVR1)
• 1984 - Release 2 (SVR2)
• 1985 - SVID version 1 (based on SVR2)
• 1986 - Release 3 (SVR3)
• 1986 - SVID version 2 (based on SVR3)
• 1988 - Release 4 (SVR4)
• 1989 - SVID version 3 (based on SVR4)
• 1996 - SVID version 4 (updated for compliance with XPG4 and POSIX 1003.1-1990)

Barkley Software Distribution

Developed and distributed by the Computer Research Group of the University of California Barkley from 1977 and 1995. Shared the initial codebase and design with the original AT&T UNIX operating system.

• 1977 - First release
• 1983 - Version 4.2
• 1986 - Version 4.3
• 1994 - Version 4.4. The first release with no AT&T code, freely distributable (BSD-4.4 Lite)

Others

• FreeBSD - Based on BSD4.4 Lite
• Linux - Developed in 1991 by Linus Torwards in replacement to Minix
• Mac OS X - Based on “Darwin”. From 10.5 certified as UNIX Sistem.
• Solaris - Based on SVR4. Developed by Sun (now Oracle).
• Open Solaris - Open Source successor of Solaris (2005).