Table of Contents
    Home / Definitions / UNIX

    UNIX is a multi-user, multitasking operating system (OS) that was developed by Ken Thompson in 1969 at the Computing Science Research Center of AT&T Bell Laboratories. . It was designed to be used exclusively by programmers and intended to be used inside the Bell System. However, in the late 1970s, AT&T licensed UNIX to outside parties, where it became the widely used OS for internet servers, workstations, and mainframe computers.

    What are the parts of the UNIX operating system?

    UNIX systems are composed of several components that are bundled together to create a self-contained software application. These components include:

    • The kernel carries out basic OS functions, including accessing files, handling communications, and allocating memory. It also includes configuration, device drivers, file structures, memory management, system calls, etc.
    • The shell is an extensive program that runs continuously to provide an interactive interface between the user, source code, and computer functions. There are several shells available including the Bourne shell and C shell.
    • Documentation, including manual pages and larger files that detail major subsystems
    • Commands, which allow users to navigate the operating system and perform specific actions, as well as maintenance and general utility applications. UNIX commands are numerous and case-sensitive.

    Working with UNIX requires a powerful, versatile shell. Read up on top UNIX shells for developers at

    History of UNIX

    UNIX was created by a small team of programmers that was led by Ken Thompson and Dennis Ritchie. It was one of the first operating systems to be written in the C programming language, which meant that it could be installed on virtually any computer in which a C compiler existed. This natural portability combined with its low price made it a popular choice among universities. However, antitrust regulations prohibited Bell Labs from marketing it as a full-scale product, so it was generally regarded as more expensive than competing operating systems.

    Bell Labs distributed the operating system in its source language form, so anyone who obtained a copy could modify and customize it for their unique needs. By the end of the 1970s, dozens of UNIX derivatives were running at various sites. After its government-mandated breakup in 1982, AT&T began to market UNIX in earnest. It also began the long and arduous process of defining a standard version of UNIX.

    Today, the trademarked “UNIX” and the “Single UNIX Specification” interface are owned by The Open Group. An operating system that is certified by The Open Group to use the UNIX trademark conforms to the Single UNIX Specification. The specification is updated every few years to certify new UNIX derivatives that are aligned with UNIX V7, the last version of UNIX that was released in 1979.

    Regarding implementation of the UNIX trademark, The Open Group released the following statement in a 2003 press release:

    “As the owner of the UNIX trademark, The Open Group has separated the UNIX trademark from any actual code stream itself, thus allowing multiple implementations. Since the introduction of the Single UNIX Specification, there has been a single, open, consensus specification that defines the requirements for a conformant UNIX system. There is also a mark, or brand, that is used to identify those products that have been certified as conforming to the Single UNIX Specification, initially UNIX 93, followed subsequently by UNIX 95, UNIX 98 and now UNIX 03. Both the specification and the UNIX trademark are managed and held in trust for the industry by The Open Group.”

    What are the different types of UNIX?

    A few years ago, there were only two main versions of UNIX available, the line of UNIX OS releases that started at AT&T (the latest version is SVR4) and the line from the University of California at Berkeley (the latest version is BSD 4.4).

    Nowadays, there are several versions including UNIX System V, SCO UNIX, ULTRIX, Portable Operating System Interface (POSIX), SunOS, HP/UX, Solaris, and AIX.

    The System V Release 4 (SVR4) was one of the most commercially successful versions of UNIX operating systems. However, the most popular versions of UNIX are Mac OS X, Linux/GNU, and Sun Solaris.

    Two common free versions of UNIX include Linux and FreeBSD. Although, most of the UNIX versions can also work with window systems.

    UNIX vs. Linux

    Although Linux is not a direct derivative of UNIX, it was born out of the desire for an open source alternative to UNIX and leverages several BSD components. Today’s Linux distributions originated in the early 1990s with Richard Stallman’s GNU (“GNU’s Not Unix!”) project. Stallman wanted to create an operating system that was adjacent to the proprietary UNIX but was widely available and free to use. However, this proved to be an implementation challenge without a dedicated kernel.

    Linus Torvald’s Linux kernel combined GNU components with open source BSD components and MIT’s X Window System to bring Linux distributions to life as they’re known today. The open source nature of Linux operating systems has spurred hundreds of unique distributions that are popular for personal and commercial use alike.

    Some practical differences between UNIX and Linux systems are distinct:

    Linux UNIX
    Source model Open-source Usually proprietary (some distributions are open source)
    License type Public license Proprietary license
    Cost Usually free (some distributions are paid) Usually more expensive (some distributions are free or device-dependent)
    Language Multilingual English
    Standard No current standardization Single UNIX Specification
    Kernel approach Monolithic Monolithic, microkernel, or hybrid
    Default shell BASH (Bourne Again Shell) Bourne Shell
    Threat recognition and resolution speed Faster (community-based) Slower (patch dependent)
    Intended use Personal or professional Professional
    Distribution examples Ubuntu, Fedora, Red Hat, Android Solaris, HP-UX, macOS


    What is a UNIX command?

    A UNIX command is a program inbuilt with UNIX OS that can be invoked in several ways. UNIX commands work interactively from a UNIX terminal, which is a graphical program that provides a command-line interface using a shell program.

    The commands are used for several purposes including getting information, manipulating data, displaying and linking files, network communication, and more. Some basic commands include:

    ls (lists files)

    mv (rename or move files)

    cd (changes directory)

    mkdir (creates new directory)

    history (shows history of previous commands)

    Not all UNIX commands are universal, so some are specific to the device on which UNIX is being used. This list contains more examples of basic commands and how they are used.

    What is a UNIX Timestamp?

    The UNIX Timestamp is a way of time tracking that refers to the total number of seconds spent since the UNIX Epoch on January 1, 1970 (at UTC), excluding leap seconds.. However, the UNIX Timestamp will cease to work due to a 32-bit overflow on January 19, 2038. Then, it will either need to be migrated to 64-bit systems or to adopt a new convention for the UNIX Timestamp.

    What purpose does UNIX serve?

    UNIX is widely used for internet servers, workstations, and mainframe computers for functions such as:

    • Multi-tasking: It is designed with sharing in mind. Commonly used for web servers, UNIX allows multiple persons from different locations to log in to the same machine at the same time.
    • Host of services: UNIX hosts are slightly different from choosing other hosting. Using UNIX can simplify the file model compared to other operating systems. A UNIX host can be a good choice for a wide range of websites.
    • Network protocol: UNIX operating systems use TCP/IP networking protocols, using mostly IP for the network layer. It is usable for relatively inexpensive computers and widely used by the communities.
    • Command-line functionality: UNIX popularized the idea of the command interpreter. The UNIX shell developed the same language for scripting and interactive commands, inspiring many other command-line interpreters.

    What are UNIX’s key features?

    UNIX has all of the features that an operating system must have, but UNIX also offers other features different from other OSs, including:

    • Multitasking and multiuser operations
    • Building-block approach to programming
    • Programming interface
    • Built-in networking (TCP/IP is standard)
    • Graphical user interfaces
    • Text processing and formatters
    • UNIX toolkit
    • Pipes and filters

    What are UNIX’s benefits?

    UNIX provides true machine independence, multiuser operations, multitasking, hierarchical file system, protected memory operation, and minimal memory uses. In this operating system, everything is a file, including the devices and terminal that simplify the input and output operations.

    UNIX also provides full multitasking with protected memory and solid user security through validation and authentication.

    What alternatives are available?

    UNIX forms the foundation of numerous operating systems.

    • BSD
    • CentOS
    • CloudLinux
    • Darwin
    • Debian
    • DragonFly BSD
    • Fedora
    • FreeBSD
    • Gentoo
    • HP-UX
    • Linux
    • macOS
    • Mageia
    • Mandriva
    • Minix
    • NetBSD
    • OpenBSD
    • PCLinuxOS
    • Raspbian
    • Red Hat
    • Scientific Linux
    • Solaris
    • SuSE
    • Trisquel
    • Turbolinux
    • Ubuntu

    Recent UNIX Coverage

    Protecting Your UNIX Infrastructure | ServerWatch

    What is Linux’s Advantage of UNIX? | TechRepublic Forums

    IT Services Firm Enhances UNIX Security While Simplifying Management | TechRepublic Whitepaper


    This article was reviewed and updated in March 2022 by Al Mahmud Al Mamun.