So What Is ‘Unix,’ Anyway?
Unix, most people would say, is an operating system written decades ago at AT&T’s Bell Labs, and its descendents. Today’s major versions of Unix branched off a tree with two trunks: one emanating directly from AT&T and one from AT&T via the University of California, Berkeley. The stoutest branches today are AIX from IBM, HP-UX from Hewlett-Packard and Solaris from Sun Microsystems.
However, The Open Group, which owns the Unix trademark, defines Unix as any operating system it has certified as conforming to the Single Unix Specification (SUS). This includes operating systems that are usually not thought of as Unix, such as Mac OS X Leopard (which descended from BSD Unix) and IBM’s z/OS (which descended from the mainframe operating system MVS), because they conform to the SUS and support SUS APIs. The basic idea is that it is Unix if it acts like Unix, regardless of the underlying code.
A still broader definition of Unix would include Unix-like operating systems—sometimes called Unix “clones” or “look-alikes”—that copied many ideas from Unix but didn’t directly incorporate code from Unix. The leading one of these is Linux.
Finally, although it’s reasonable to call Unix an “operating system,” as a practical matter it is more. In addition to an OS kernel, Unix implementations typically include utilities such as command-line editors, APIs, development environments, libraries and documentation.
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.”