Unix turns 40: The past, present and future of the OS

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In 1987, Unix System Laboratories, a part of Bell Labs at the time, began working with Sun on a system that would unify the two major Unix branches. The product of their collaboration, called Unix System V Release 4.0, became available two years later and combined features from System V Release 3, BSD, SunOS and Microsoft Corp.'s Xenix.

Other Unix vendors feared the AT&T/Sun alliance. The various parties formed competing "standards" bodies with names like X/Open; Unix International; Corporation for Open Systems; and the Open Software Foundation, which included IBM, HP, DEC and others allied against the AT&T/Sun partnership. The arguments, counterarguments and accomplishments of these groups would fill a book, but they all claimed to be taking the high road to a unified Unix while firing potshots at one another.

In an unpublished paper written in 1988 for the Defense Advanced Research Projects Agency, the noted minicomputer pioneer Gordon Bell said this of the just-formed Open Software Foundation: "OSF is a way for the Unix have-nots to get into the evolving market, while maintaining their high-margin code museums.' "

The Unix Wars failed to settle differences or set a true standard for the operating system. But in 1993, the Unix community received a wake-up call from Microsoft in the form of Windows NT, an enterprise-class, 32-bit multiprocessing operating system. The proprietary NT was aimed squarely at Unix and was intended to extend Microsoft's desktop hegemony to the data center and other places dominated by the likes of Sun servers.

Microsoft users applauded. Unix vendors panicked. The major Unix rivals united in an initiative called the Common Open Software Environment and the following year more or less laid down their arms by merging the AT&T/Sun-backed Unix International group with the Open Software Foundation. That coalition evolved into The Open Group, the certifier of Unix systems and owner of the Single Unix Specification, which is now the official definition of Unix.

As a practical matter, these developments may have "standardized" Unix about as much as possible, given the competitive habits of vendors. But they may have come too late to stem a flood tide called Linux, the open-source operating system that grew out of Tanenbaum's Minix.

The Future of Unix

A recent poll by Gartner Inc. suggests that the continued lack of complete portability across competing versions of Unix, as well as the cost advantage of Linux and Windows on x86 commodity processors, will prompt IT organizations to migrate away from Unix.

"The results reaffirm continued enthusiasm for Linux as a host server platform, with Windows similarly growing and Unix set for a long, but gradual, decline," says the poll report, published in February.

"Unix has had a long and lively past, and while it's not going away, it will increasingly be under pressure," says Gartner analyst George Weiss. "Linux is the strategic 'Unix' of choice." Although Linux doesn't have the long legacy of development, tuning and stress-testing that Unix has seen, it is approaching and will soon equal Unix in performance, reliability and scalability, he says.

But a recent Computerworld survey suggests that any migration away from Unix won't happen quickly. In the survey of 211 IT managers, 90% of the 130 respondents who identified themselves as Unix users said their companies were "very or extremely reliant" on Unix. Slightly more than half said that "Unix is an essential platform for us and will remain so indefinitely," and just 12% agreed with the statement "We expect to migrate away from Unix in the future." Cost savings, primarily via server consolidation, was cited as the No. 1 reason for migrating away.

Weiss says the migration to commodity x86 processors will accelerate because of the hardware cost advantages. "Horizontal, scalable architectures; clustering; cloud computing; virtualization on x86 -- when you combine all those trends, the operating system of choice is around Linux and Windows," he says.

"For example," Weiss continues, "in the recent Cisco Systems Inc. announcement for its Unified Computing architecture, you have this networking, storage, compute and memory linkage in a fabric, and you don't need Unix. You can run Linux or Windows on x86. So, Intel is winning the war on behalf of Linux over Unix."

The Open Group concedes little to Linux and calls Unix the system of choice for "the high end of features, scalability and performance for mission-critical applications." Linux, it says, tends to be the standard for smaller, less critical applications.

AT&T's Korn is among those still bullish on Unix. Korn says a strength of Unix over the years, starting in 1973 with the addition of pipes, is that it can easily be broken into pieces and distributed. That will carry Unix forward, he says: "The [pipelining] philosophy works well in cloud computing, where you build small, reusable pieces instead of one big monolithic application."

Regardless of the ultimate fate of Unix, the operating system born at Bell Labs 40 years ago has established a legacy that's likely to endure for decades more. It can claim parentage of a long list of popular software, including the Unix offerings of IBM, HP and Sun, Apple Inc.'s Mac OS X and Linux. It has also influenced systems with few direct roots in Unix, such as Microsoft's Windows NT and the IBM and Microsoft versions of DOS.

Unix enabled a number of start-ups to succeed by giving them a low-cost platform to build on. It was a core building block for the Internet and is at the heart of telecommunications systems today. It spawned a number of important architectural ideas, such as pipelining, and the Unix derivative Mach contributed enormously to scientific, distributed and multiprocessor computing.

The ACM may have said it best in its 1983 Turing Award citation in honor of Thompson and Ritchie's Unix work: "The genius of the Unix system is its framework, which enables programmers to stand on the work of others."

Anthes is a freelance writer in Arlington, Va.

Timeline: 40 Years of Unix


AT&T-owned Bell Laboratories withdraws from development of Multics, a pioneering but overly complicated time-sharing system. Some important principles in Multics were to be carried over into Unix.

Ken Thompson at Bell Labs writes the first version of an as-yet-unnamed operating system in assembly language for a DEC PDP-7 minicomputer.


Thompson's operating system is named Unics, for Uniplexed Information and Computing Service, and as a pun on "emasculated Multics." (The name would later be mysteriously changed to Unix.)


Unix moves to the new DEC PDP-11 minicomputer.

The first edition of the Unix Programmer's Manual, written by Thompson and Dennis Ritchie, is published.


Ritchie develops the C programming language.


Unix matures. The "pipe" is added to Unix; this mechanism for sharing information between two programs will influence operating systems for decades. Unix is rewritten from assembler into C.


"The UNIX Timesharing System," by Ritchie and Thompson, appears in the monthly journal of the Association for Computing Machinery. The article produces the first big demand for Unix.


Bell Labs programmer Mike Lesk develops UUCP (Unix-to-Unix Copy Program) for the network transfer of files, e-mail and Usenet content.


Unix is ported to non-DEC hardware, including the IBM 360.


Bill Joy, a graduate student at UC Berkeley, sends out copies of the first Berkeley Software Distribution (1BSD), essentially Bell Labs' Unix v6 with some add-ons. BSD becomes a rival Unix branch to AT&T's Unix; its variants and eventual descendents include FreeBSD, NetBSD, OpenBSD, DEC Ultrix, SunOS, NeXTstep/OpenStep and Mac OS X.


4BSD, with DARPA sponsorship, becomes the first version of Unix to incorporate TCP/IP.


Bill Joy co-founds Sun Microsystems to produce the Unix-based Sun workstation.


AT&T releases the first version of the influential Unix System V, which would later become the basis for IBM's AIX and Hewlett-Packard's HP-UX.


X/Open Co., a European consortium of computer makers, is formed to standardize Unix in the X/Open Portability Guide.


AT&T publishes the System V Interface Definition, an attempt to set a standard for how Unix works.


Rick Rashid and colleagues at Carnegie Mellon University create the first version of Mach, a replacement kernel for BSD Unix.


AT&T Bell Labs and Sun Microsystems announce plans to co-develop a system to unify the two major Unix branches.

Andrew Tanenbaum writes Minix, an open-source Unix clone for use in computer science classrooms.


The "Unix Wars" are under way. In response to the AT&T/Sun partnership, rival Unix vendors including DEC, HP and IBM form the Open Software Foundation (OSF) to develop open Unix standards. AT&T and its partners then form their own standards group, Unix International.

The IEEE publishes Posix (Portable Operating System Interface for Unix), a set of standards for Unix interfaces.


Unix System Labs, an AT&T Bell Labs subsidiary, releases System V Release 4 (SVR4), its collaboration with Sun that unifies System V, BSD, SunOS and Xenix.


The OSF releases its SVR4 competitor, OSF/1, which is based on Mach and BSD.


Sun announces Solaris, an operating system based on SVR4.

Linus Torvalds writes Linux, an open-source OS kernel inspired by Minix.


The Linux kernel is combined with GNU to create the free GNU/Linux operating system, which many refer to as simply "Linux."


AT&T sells its subsidiary Unix System Laboratories and all Unix rights to Novell. Later that year, Novell transfers the Unix trademark to the X/Open group.

Microsoft introduces Windows NT, a powerful, 32-bit multiprocessor operating system. Fear of NT spurs true Unix-standardization efforts.


X/Open merges with the OSF to form The Open Group.


Thompson and Ritchie receive the National Medal of Technology from President Clinton.


The Open Group announces Version 3 of the Single Unix Specification.

This story, "Unix turns 40: The past, present and future of the OS" was originally published by Computerworld.

Copyright © 2009 IDG Communications, Inc.

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