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While they are often mentioned together and may sound similar, UNIX and Linux are not the same. Nonetheless, their history, their evolution and their peculiarities have indelibly marked the evolution of information technology and server environments in particular. Although Linux has many features in common with UNIX, it is not really UNIX. This post explores the differences, history and reasons for this relationship between the two most influential operating systems in the computing world.
The birth of UNIX – Between laboratories and universities
It all began in the 70s, when in the AT&T Bell laboratories, Ken Thompson and Dennis Ritchie developed an operating system which they called “UNIX”. This innovation brought with it a wave of change in the computing world, being one of the first operating systems written in a high-level language, C, rather than assembly language.
Over the years, UNIX code was shared with numerous universities and corporations, including the University of California, Berkeley. The latter developed its own version of UNIX, called BSD (Berkeley Software Distribution), leading to a significant dispute with Bell Laboratories over copyright issues.
In the 70s and 80s, as technological innovation was gaining momentum, UNIX emerged as a driving force. The UNIX code was generously shared with numerous academic institutions and corporations around the world, a gesture that would influence the future trajectory of the technology sector. Among these institutions, the University of California, Berkeley, played an especially significant role in the development of UNIX.
Berkeley, recognized for its strong emphasis on research and innovation, quickly adopted UNIX for its own purposes. In particular, the research team led by Professor Ken Thompson at Berkeley began work on its own version of the UNIX operating system, which became known as BSD, or Berkeley Software Distribution.
BSD differed from UNIX in several key respects. Berkeley's developers introduced many innovations and improvements, including an improved file system, better process management, and the introduction of new network protocols, most notably the TCP/IP protocol suite, which became the standard for the Internet.
However, despite BSD's success and prominence, its development was not without controversy. In particular, AT&T, which held the rights to UNIX at the time, filed a lawsuit against the University of California, claiming that BSD violated their copyrights. This legal wrangling, known as "the UNIX War," caused a rift between the two entities and marked a turning point in the history of UNIX.
This legal conflict was resolved only after several years, in 1994, when the University of California and AT&T reached an agreement. BSD was finally freed of any legal claims, allowing it to go fully open source. This event marked the birth of many variants of BSD, including FreeBSD, NetBSD and OpenBSD, which continue to be developed and used today.
So while the University of California, Berkeley has faced a significant spat with Bell Laboratories, its dedication to developing BSD has had a lasting impact. BSD not only helped shape the future direction of UNIX, it also laid the foundation for the rise of open source software, a movement that transformed the technology industry as a whole.
Regarding the history of UNIX we have dealt with a vertical and extremely specific post on what UNIX is and its history.
The patchwork of commercial UNIX systems
After the invention of UNIX, several commercial versions of the operating system saw the light of day. Among these, SunOS (by Sun Microsystems, later acquired by Oracle), XENIX (originally developed by Microsoft), SCO Unix (by Santa Cruz Operation), AIX (by IBM) and finally, MacOS, the operating system developed by Apple which under the hood it uses a UNIX-based core.
These variants of UNIX, while differing from each other in specific details, retain the core functionality and philosophies of the original UNIX design, although each has made its own improvements and changes.
UnixWare is a UNIX operating system first developed in the 90s, with a rather complex history due to numerous changes in ownership and management.
Its initial development was under the umbrella of Univel, a joint venture between Novell and AT&T's Unix System Laboratories (USL). The operating system, based on UNIX's System V Release 4.2, was conceived as Novell's attempt to consolidate the UNIX market, at a time when UNIX was a point of reference for server operating systems. The first release of UnixWare, known as UnixWare 1.0, occurred in 1992.
However, in 1993, Novell fully acquired USL and absorbed Univel, bringing UnixWare under its direct control. Following this acquisition, Novell developed and released UnixWare 2.0 in 1994. But Novell's attempt to consolidate the UNIX market was not as successful as hoped, and in 1995 it sold the rights to UnixWare to the Santa Cruz Operation (SCO).
Under SCO, UnixWare continued to be developed and released, with new versions introducing improvements and additional features. In 2001, SCO was restructured and renamed Tarantella, Inc., while a new company, called Caldera Systems, acquired UnixWare and other UNIX assets. Caldera, which would later become The SCO Group, continued the development of UnixWare.
Today, UnixWare is maintained by Xinuos, a company that acquired the operating system rights from The SCO Group in 2011. UnixWare 7, the last major release, is still being developed and supported, with the latest release – UnixWare 7.1.4 + – released in 2018.
While UnixWare is no longer a dominant player in the operating system market, as it once was, it remains a piece of history in the UNIX world. Its evolution reflects the complex vicissitudes of the UNIX market in the 90s and 2000s, with its tortuous path through a series of companies and consolidation attempts.
HP-UX, or Hewlett-Packard UniX, is a UNIX-like operating system first released in 1984. Developed by one of the technology industry giants, Hewlett-Packard (HP), HP-UX has been a major player in prominent in the UNIX landscape for decades.
HP-UX was born out of HP's need to have a proprietary operating system for its workstations and servers. The first release of HP-UX was based on AT&T's System III, but later versions incorporated elements from System V and also from BSD, another variant of UNIX.
HP-UX was one of the first UNIX operating systems to be officially certified under The Open Group's “Single UNIX Specification” standard. This made it one of the few "true" UNIXes on the market, by the strict definition of the term.
Over the years, HP-UX has introduced many innovations and advanced features. These include the addition of support for shared memory systems and the introduction of a powerful programming interface for multi-threading, known as “pthreads”. Another notable feature of HP-UX was its emphasis on security and reliability, with features such as process isolation and fault resiliency.
HP-UX has found widespread use in industries such as engineering, finance, and education, where its robustness and power have enabled it to handle critical and complex applications. However, with the rise of Linux and the gradual transition to open source systems, HP has slowly reduced its investment in HP-UX. Despite this, HP-UX continues to be supported and used in some environments, particularly where business continuity is essential.
The history of HP-UX reflects in many ways the developmental arc of UNIX operating systems in general, from their origins in corporate server rooms and universities, through the UNIX market explosion of the 80s and 90s, to relative decline in the first part of the XNUMXst century. Despite the changes in the technology landscape, HP-UX remains a testament to UNIX's lasting impact on the world of operating systems.
Before Solaris, there was SunOS – the original UNIX operating system developed by Sun Microsystems. The first release of SunOS was in 1982, a few years after the company was founded. SunOS was developed on the basis of BSD, a version of UNIX created at the University of California, Berkeley, respecting its spirit of openness and flexibility.
SunOS was a key incarnation of UNIX during the 80s. The operating system incorporated significant improvements and innovative features over previous versions of UNIX, including expanded support for networking – a crucial element that would define Sun's place in the server and workstation market.
For nearly a decade, SunOS was the mainstay of Sun Microsystems' portfolio, helping to establish the company's reputation as a leader in UNIX-based operating systems. However, in 1992, Sun decided to go a step further and launched Solaris, an operating system which, while maintaining the legacy of SunOS, was destined to become one of the most influential and widely used variants of UNIX.
The history of SunOS offers an important perspective on the birth and development of commercial UNIX systems. Its success and impact on the industry laid the foundation for the rise of Solaris, highlighting Sun Microsystems' pivotal role in the history of UNIX.
Solaris, one of the leading commercial operating systems based on UNIX, represents a fundamental chapter in the history of this type of system. Originally launched by Sun Microsystems in 1992, Solaris derived from the previous SunOS, while maintaining a close link with the UNIX tradition. Sun Microsystems was known for its role in the server and workstation systems industry, and Solaris soon became one of the mainstays of their offering.
Solaris was distinguished by several innovative features. The operating system introduced advanced networking and security features, such as the ZFS file system, which offered robust and flexible data management, and Solaris Zones, an operating system virtualization system. Solaris was also one of the first operating systems to introduce kernel-level support for multithreading, a feature that allows more efficient use of multi-core processors.
In 2010, however, the Solaris story took a dramatic turn. Sun Microsystems was acquired by Oracle Corporation, and management of the operating system passed into the hands of the new owner. Despite initial promises to maintain the open source orientation of Solaris, Oracle changed tack, limiting access to source code and introducing a more restrictive licensing model.
Despite these changes, Solaris continued to exert significant influence in the UNIX operating system landscape, especially in high-performance applications and data centers. Its story, from its innovative origins at Sun Microsystems to its controversial acquisition by Oracle, is an important part of the larger narrative of UNIX and its derivative operating systems.
XENIX represents a fascinating chapter in the history of UNIX operating systems. Launched by Microsoft in the late 70s, XENIX was one of the first attempts to bring UNIX to a variety of hardware platforms, including personal computers.
The history of XENIX begins when Microsoft acquired a license for the Version 7 UNIX source code from AT&T in 1979. Microsoft's goal was to adapt UNIX to be compatible with the most popular hardware systems of the time, including machines based on Intel 8086 and 8088 processors.
During its early years, XENIX was actually the most widely used UNIX system, thanks to its versatility and support for a wide range of architectures. Microsoft, however, never directly marketed XENIX to end consumers, instead preferring to license the operating system to other companies, including SCO (Santa Cruz Operation), which became one of the largest distributors of XENIX.
Despite its initial success, XENIX's history was relatively short. With the advent of MS-DOS, Microsoft gradually stopped supporting XENIX, finally handing over all rights to SCO in 1987. Despite this, the XENIX legacy persists. The operating system helped popularize UNIX on a wide range of hardware and laid the foundation for the development of SCO UNIX, which played an important role in the operating system industry for several years to come.
Santa Cruz Operation (SCO) was a pioneer in the world of UNIX operating systems. Its best-known incarnation of UNIX, SCO UNIX, has been a driving force in the commercial operating system market for more than a decade.
The history of SCO UNIX begins in 1983, when the Santa Cruz Operation began distributing its own version of UNIX for machines based on the x86 architecture. However, SCO's influence grew exponentially after Microsoft acquired the rights to XENIX in 1987. This acquisition allowed SCO to develop and distribute its own full version of UNIX, giving birth to SCO UNIX.
SCO UNIX became known for its stability, networking capabilities, and ability to support large numbers of concurrent users, making it a popular choice for businesses. In addition, SCO played a crucial role in making UNIX accessible to Intel-based PCs, helping pave the way for Linux and other UNIX-based operating systems to spread throughout the PC world.
The history of SCO and SCO UNIX, however, has not been without controversy. In 2003, the company, renamed "The SCO Group," filed a series of lawsuits claiming to own the copyrights to the UNIX source code, also implicating Linux in those claims. These legal disputes, known as “the SCO war,” have sparked intense intellectual property discussions in the world of open source software.
Despite the controversy, SCO UNIX's legacy remains important. The operating system played a pivotal role in the evolution of UNIX, helping to shape the universe of operating systems as we know it today.
AIX from IBM
AIX, the Advanced Interactive eXecutive, is IBM's contribution to the universe of UNIX operating systems. Developed and first released in 1986, AIX represents IBM's attempt to create a powerful, reliable, and versatile UNIX operating system suitable for a wide variety of business applications.
The journey of AIX begins with a series of strategic decisions made by IBM in the 80s, when the company decided to shift its focus away from its traditional mainframe product lines to explore the growing market for UNIX operating systems. AIX incorporated several innovations, including a journaling-based file system for increased reliability, a powerful shell environment, and a rich graphical user interface.
AIX reached its peak in the early 90s with the introduction of the IBM RS/6000 servers, which became known for their high-end performance. AIX was optimized for these machines, and the two together formed a powerful combination that has found success in numerous business applications.
Despite the rise of Linux in the late 90s and early 2000s, AIX has maintained a strong presence in the operating system market. IBM has continued to develop and support AIX, adapting to changing market needs and maintaining a commitment to deliver a high-quality, robust UNIX operating system.
The story of AIX represents a significant part of IBM's journey through the UNIX era, and remains a prime example of how a company can shape and adapt an operating system to meet the needs of a changing market.
macOS from Apple
MacOS, the desktop operating system developed by Apple, is one of the best known and most widely used incarnations of UNIX in the modern era. Despite its sleek and user-friendly exterior, the heart of macOS beats with the rhythm of UNIX, reflecting its roots in the tradition of this operating system.
The history of MacOS as a UNIX system begins with its tenth version, MacOS X, released in 2001. This version marked a turning point for Apple, as it was built on a completely new foundation - Darwin. Darwin is an open source operating system based on several free software components, including the XNU kernel, the BSD system, and many GNU utilities. Of particular note is the adoption of the Mach kernel, which provides MacOS with some of its multitasking and memory management capabilities.
One of the fundamental aspects of MacOS is that it is not simply a "UNIX-like" system, but is officially recognized as a true UNIX operating system. Starting with MacOS X 10.5 Leopard, Apple has obtained UNIX certification from The Open Group, the consortium that owns the rights to the UNIX trademark. To obtain this certification, an operating system must comply with a series of precise and specific standards, known as the Single UNIX Specification.
Apple's decision to adhere to these standards and become UNIX certified had a number of significant implications. It allowed MacOS to benefit from the stability, security, and portability of UNIX while maintaining the ease of use and clean aesthetics that have become Apple's trademark.
Today, macOS continues to uphold the tradition of UNIX by providing a stable and powerful platform for a wide range of users, from creative professionals to software developers. Apple's choice to build MacOS on a UNIX foundation demonstrated the versatility and resilience of UNIX, highlighting how this operating system, born half a century ago, remains relevant in the modern age of technology.
The UNIX brand and certified operating systems
To resolve the confusions created by the proliferation of UNIX variants, the UNIX brand was created, now managed by The Open Group, a consortium of companies including IBM, Hewlett-Packard and Oracle Corporation. According to The Open Group, only operating systems that meet precise specifications and pass a certification process can bear the UNIX seal.
Thus, when we speak of "UNIX", we generally refer to all operating systems that derive from the original AT&T UNIX, even if only those certified by The Open Group can officially use that denomination.
The creation of the UNIX brand and association with the Single UNIX Specification marked an important moment in the history of UNIX operating systems. In a world of increasingly diverse UNIX variants, The Open Group has sought to establish a set of standards to ensure some consistency between different systems claiming the UNIX pedigree.
The Single UNIX Specification is a detailed set of programming and system interface standards that an operating system must meet in order to be considered a "true" UNIX operating system. These standards cover a wide range of aspects, from kernel interaction and process management, to file and directory manipulation, to network interfaces.
The main objective of these standards is to ensure the portability of the software. In other words, a program written for one operating system that complies with the Single UNIX Specification should be able to run on another system that complies with the same standards, with little or no modifications. This portability is critical for software developers, allowing them to reach a wide variety of systems with the same code.
To obtain the UNIX Mark, an operating system must pass a rigorous certification process that verifies its compliance with the Single UNIX Specification. This process includes a series of tests that verify the correct implementation of the specified interfaces and features. Only systems that successfully pass this certification process are allowed to use the UNIX trademark.
The Single UNIX Specification and the UNIX branding represent a significant effort to maintain some consistency in the UNIX ecosystem. Despite the many variations of UNIX that exist, these standards help ensure that the philosophy and core principles of UNIX – portability, multitasking, robustness – remain at the core of these operating systems.
“UNIX-Like” and the Birth of Linux
As commercial UNIX systems continued to evolve and branch out into numerous variants, a different current of thought took root in the computing community. Numerous groups and individuals set out to recreate the power and versatility of UNIX, but with one important difference: they would not use the original UNIX source code. These new operating systems, which mirrored the spirit and functionality of UNIX but were developed independently, were classified as "UNIX-like".
One of the first and most influential "UNIX-like" systems was MINIX. Created by computer science professor Andrew Tanenbaum, MINIX was conceived as an educational project. Its realization had the objective of providing students with an open and understandable source operating system, on which they could learn the key concepts of operating system design. But it was another "UNIX-like" project that left an indelible mark on the history of computing: we're talking about Linux.
Linux was born in 1991, fruit of the genius and determination of Linus Torvalds. Initially, Linux was not a complete operating system, but "only" a kernel, i.e. the heart of the operating system responsible for managing hardware resources and communicating between the various system components. Building a complete operating system required much more than a kernel: tools, utilities, application programs were needed. And this is where the GNU Project came in.
The GNU project was started by Richard Stallman in 1983, with the ambition of creating a free and fully UNIX compatible operating system. While the project had produced a number of very useful tools and applications, it still lacked a key component: a working kernel. The arrival of Linux filled this gap.
The union of GNU utilities with the Linux kernel led to the creation of what we know today as "Linux", although in technical terms it would be more accurate to refer to it as "GNU/Linux", to recognize the fundamental contribution of both projects. This combination has given rise to a powerful, flexible and, equally important, completely free and open source operating system, fully embodying the philosophy of sharing and collaboration that underlies the free software movement.
Linux and the various distributions.
When we talk about Linux, we enter a vast universe in which the word "distribution" is of central importance. Unlike UNIX, which tends to be a cohesive and stable operating system, the Linux world is divided into a large number of different distributions, each with its own peculiarities, purposes and target users. This wide variety of options is one of the driving forces that have made Linux one of the most popular and versatile open-source operating systems.
The term “distribution” in the Linux context refers to a complete operating system based on the Linux kernel. Each distribution includes the Linux kernel, a set of software libraries and utilities, a desktop environment, and a package manager that facilitates installing, updating, and removing software. Despite the same foundation, each distribution can differ significantly from the others in philosophy, structure, ease of use, or focus on particular areas of use.
Considered the oldest Linux distribution still active, Slackware is known for its philosophy of maintaining the simplicity and integrity of its systems. First released in 1993 by Patrick Volkerding, Slackware aims to offer a "pure" UNIX-like system, minimally modified from the original software. This philosophy makes it appreciated by an audience of expert users who want to have total control over their operating system.
Born in 1993 on the initiative of Ian Murdock, Debian is a Linux distribution universally appreciated for its stability and reliability. This free operating system is developed by a large community of volunteers from all over the world. Debian's strict software freedom policy, its stability, and large archive of available packages make it a popular choice for server, embedded systems, and desktop use.
Red Hat is one of the most recognized Linux distributions in the corporate world. Launched in 1994, it quickly gained popularity due to its unique business model that offers open source software with paid professional support. Red Hat Enterprise Linux (RHEL) is known for its stability and security, and is widely used in corporate servers. In 2018, IBM acquired Red Hat, underlining the importance of Linux in the enterprise world.
Gentoo is a unique Linux distribution known for its source-based distribution model. Instead of providing pre-compiled packages, Gentoo allows users to compile software directly from source, optimizing it for their hardware specifications. This flexibility makes Gentoo a popular choice among more experienced Linux users and those who want to customize every aspect of their system.
Ubuntu, derived from Debian, is one of the most popular Linux distributions for desktop use. Created by Canonical Ltd in 2004, Ubuntu is known for its ease of use and broad community support. It offers a standard configuration with its own desktop environment, called Unity, but is also available in various "derivatives" with different desktop environments. Ubuntu has done a lot to bring Linux to the masses, making it accessible even to non-tech users.
SUSE is another distribution that has made a significant impact in the Linux world, especially in the corporate context. Originally launched in Germany in 1992, SUSE introduced many innovations to the Linux landscape, including the first graphical installation system and the powerful administration tool YaST. The commercial version, SUSE Linux Enterprise (SLE), is widely used in corporate environments, while openSUSE is the community version aimed at home users.
The Linux distributions mentioned above represent only a small part of a much larger and more varied panorama. There are specialized distributions for education, for security, for multimedia processing, for use on older hardware, and so on. This incredible diversity is one of Linux's great strengths, offering a wealth of choices hardly found in any other operating system.
The gradual transition from UNIX to Linux
The history of UNIX is dotted with a number of operating systems that have had a significant impact on the computing industry. However, as time went on, an increasing number of these historic UNIX systems ceased to exist or received support, while Linux continued to grow in strength and gain popularity. This transition has occurred due to a number of factors that have made Linux a more attractive choice for many organizations.
The world of UNIX has witnessed a variety of operating systems which, despite their strong roots and innovations, have seen their demise. These include Sun Microsystems' Solaris, one of the most powerful and versatile UNIX systems, which declined after Oracle's acquisition of Sun. Despite this, Solaris has had a significant impact on the industry, with its implementation of the ZFS filesystem and Solaris zones, among other innovations.
SCO UNIX, derived from UNIX System V first released in 1983, is another system that played a pivotal role in the evolution of UNIX. However, following a series of legal disputes and corporate problems, support for SCO UNIX was eventually discontinued.
AIX, IBM's proprietary UNIX operating system, is another example of a UNIX system that has undergone a significant change. While AIX is still supported and used, IBM has recognized the growing importance of Linux, as evidenced by its acquisition of Red Hat in 2018.
HP-UX, Hewlett-Packard's proprietary UNIX operating system, has seen a similar fate. While HP-UX is still available, Hewlett-Packard Enterprise has gradually shifted its focus towards Linux and open source.
These are just some of the UNIX systems that, over time, have lost ground or been completely replaced by Linux solutions. The flexibility, versatility, and open source nature of Linux have helped make it an increasingly popular choice among developers and organizations.
Companies traditionally tied to UNIX, such as IBM, have recognized the importance and growth of Linux. IBM's acquisition of Red Hat underscored the growing importance of Linux in the operating system landscape. This change is a clear indicator that despite the important legacy of UNIX, the future belongs to Linux and open source.
While UNIX is an operating system designed to promote a uniform and standardized programming interface, it is inevitable that many variations have arisen as its spread and adoption. This differentiation, the result of independent software evolution, has led to a number of usability complexities. While all UNIX systems are derived from the same DNA, they are also vastly different and complex when it comes to handling, particularly the commands a user can execute.
UNIX systems, from IBM AIX to Solaris from Sun Microsystems, passing through XENIX, are not interchangeable with each other. Each of these operating systems has its own quirks, starting with filesystem management, process management, and basic shell commands. These differences can create a difficult learning experience and steep learning curve for even experienced system administrators. For example, a command that works one way on an IBM AIX system might behave differently or might not exist at all on a Solaris or XENIX system. This variety requires a system administrator to acquire specific skills for each of these UNIX systems, making it difficult to switch quickly between them.
Unlike UNIX systems, the variety of Linux distributions is much less of a problem for system administrators. Although there are many Linux distributions, each with its own particularities, the adaptation from one distribution to another is relatively simpler. The Linux kernel, the heart of every distribution, remains constant, and most of the basic shell commands are standardized and work the same across distributions. This uniformity is also reflected in the system APIs, which remain almost identical between different distributions. As a result, a system administrator can switch between Linux distributions in days or weeks, compared to the months it might take to switch between UNIX systems.
This uniformity of Linux has had a significant impact on its success and adoption. System administrators appreciate the ease with which they can switch from one distribution to another, without having to learn a new set of commands or a new system API. This adaptability has allowed Linux to conquer a wide range of applications, from supercomputers to embedded devices.
However, it is important to remember that these differences between UNIX and Linux do not make one superior to the other. UNIX and Linux both have their strengths and ideal applications. UNIX, for example, has a long history of stability and reliability, making it ideal for mission-critical applications. Linux, on the other hand, has a global developer community and excellent adaptability, making it perfect for a wide variety of applications. The value of an operating system, therefore, ultimately depends on the specific needs of the user or organization using it.
The history of UNIX and Linux is complex and full of developments. UNIX, with its design philosophy and approach to operating systems, laid the foundation for much of modern computing. Linux, while a "heir" to UNIX, has followed a unique path, becoming a global phenomenon that has changed the way we think about software and its distribution. Both continue to influence the computing world in important ways, and their history and development are worth exploring and understanding.