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