The systems world will shortly be celebrating a major anniversary milestone. UNIX® is turning 40 years old! Most of us know the story of how UNIX was born, but what about why? Was it born strictly because its founders wanted to play a computer game on a different platform? And why does UNIX continue to thrive 15 years after an (in)famous Byte Magazine article that asked, "Is UNIX dead?" How has AIX® (the only UNIX flavor that has increased its market share through the years) been a part of the evolution of UNIX and what are the current trends today in the UNIX arena? These are just some of the topics this article explores.

Ken Milberg, Writer/site expert, Future Tech

Ken Milberg is a technology writer and site expert for and provides Linux technical information and support at He is also a writer and technical editor for IBM Systems Magazine, Power Systems edition, and a frequent contributor of content for IBM developerWorks. He holds a bachelor's degree in computer and information science, as well as a master's degree in technology management from the University of Maryland University College. He is the founder and group leader of the N.Y. Metro POWER-AIX/Linux Users Group. Through the years, he has worked for both large and small organizations and has held diverse positions from CIO to senior AIX engineer. He is currently president and managing consultant for UNIX-Linux Solutions, is a PMI-certified Project Management Professional (PMP), an IBM Certified Advanced Technical Expert (CATE), and is also IBM SCon certified.

01 December 2009

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The history of UNIX

The roots of UNIX date back to the late 1960s. Ken Thompson joined Bell Labs in 1966 in the Computing Research Department, which is when he started working on the Multics project, a very ambitious effort to create a next-generation portable operating system that eventually failed. Dennis Ritchie joined Bell Labs in 1968, where he also started work on Multics. This was a joint effort of Bell Labs, MIT, and GE to develop a new computer operating system. Through the efforts of Dennis Ritchie and Ken Thompson, UNIX would be developed in 1969. Ken Thompson developed a game on the GE-645 mainframe called Space Travel. Unfortunately, the game was just running too slow on the GE box, so Thompson rewrote (in assembly) the game for DEC's PDP-7, with the help of Dennis Ritchie. The porting experience led Ken to develop a new OS for the PDP-7. This included a file system as well as the new multi-tasking operating system itself. They included a command-line interpreter and some small utility programs.

The project was originally named Unics, and it could eventually support two simultaneous users, which led to some financial support from Bell. In 1970, UNIX became the official name for the operating system, which ran on the PDP-11/20. It also included roff (a text formatting program) and a text editor. Ultimately, it was rewritten in C in 1973, which made it portable and changed the history of operating systems.

Why was UNIX created? While the porting of the game may have been the impetus, there were other factors at work. It was clear that programmers needed a way to share resources on the same box and multitask. These innovators recognized the need for an OS that addressed issues of portability, muli-tasking, and multi-user capability.

How has UNIX evolved and thrived?

Through the 1970s, UNIX went through many iterations and steadily gained popularity. In 1977, the first commercial version became available through Interactive Systems. It was during this time that the University of California at Berkeley was also working to improve UNIX. They released their distribution, the BSD version, which included the C shell. The AT&T version evolved into release 7 in 1978, which included the Bourne shell. In 1983, AT&T System V came to be with an installed base of 45,000 users. Around this time, the University of California at Berkeley released 4.2BSD, which included TCP/IP. This is where the cold war started -- System V versus BSD.

In 1986, NFS shipped. AIX was also first announced at around this time. UNIX already had an installed base of about a 250,000 users. In 1989, in an attempt to solidify its market leadership, AT&T announced a pact with Sun Microsystems, the leading proponent of the Berkeley-derived strain of UNIX. This evolved into what would become System V, release IV. This release actually unified System V, BSD, and Xenix. At this time, the installed UNIX base was over one million users.

In early 1993, AT&T sold its rights to Novell, which was looking for an OS to standardize around. Novell did not manage this correctly, which they learned a few years later when they entered the Linux® arena with SUSE. Eventually SCO bought the UNIX Systems business from Novell, and UNIX system source code and technology continues to be developed by SCO. As SCO did not make much money from this acquisition, they actually tried to use litigation as a revenue stream years later when they sued Linux distributors, claiming that Linux stole the source code from UNIX. IBM was even part of that suit, as they supported Linux distributions. Eventually, SCO lost their case.

Today, there are three manufacturers that really dominate UNIX: HP (HP-UX), Sun (Solaris), and IBM® (AIX). Most users of UNIX are not really concerned as much about ancillary factors such as BSD or System V commands, but are more concerned with RAS (Reliability, Availability, and Scalability) factors, performance, virtualization, and hardware integration. More than any other factor, this has been why IBM has been more successful in recent years.


SunOS version 1.0 was first introduced in 1983, along with support for Sun-1 and Sun-2 systems. SunOS Version 2.0, introduced in 1985, came out with the virtual file system (VFS) and NFS. In 1987, AT&T and Sun first announced that they would work together to help merge System V and BSD into one release, based on System V, release 4. SunOS was originally developed from the BSD flavor of UNIX in 1983. It was later rebranded as Solaris (starting with version 5), based on AT&T System V release IV, in 1993. The first 64-bit version of Sparc Solaris 7 would add support for file system metadata logging. Solaris 9, introduced in 2002, added support for Solaris Volume Manager and Linux capabilities. Their most important release would be Solaris 10, which was first introduced in 2005 and included many new features such as support for its new ZFS file system, Solaris Containers, and Logical Domains.


Version 1 of HP's UNIX (HP-UX) was first released in 1984. It was originally based on System V, release 3, and it ran exclusively on their RISC - PA-RISC HP 9000 platform. Version 9 introduced its character-based graphical user interface (GUI), SAM, which allowed you to administrator the system without using the command line. Version 10 was introduced in 1995, which brought changes in the layout of the system file and directory structure, making it strikingly similar in many ways to AT&T SVR4. Version 11 was first introduced in 1997. This was HP's first release to support 64-bit addressing. In 2000, 11i came to be, which introduced operating environments, defined as bundled groups of layered applications for specific IT purposes. In 2001, Version 11.20 introduced support for Itanium systems. Interestingly enough, HP-UX was the first UNIX that used Access Control Lists (ACLs) for file permissions. It was also one of the first to introduce built-in support for Logical Volume Manager.

Why has UNIX thrived?

Many of us still remember that Byte Magazine article in 1990 that wondered "Is UNIX dead?" The timing was around the impending release of Windows NT®. Twenty years later, most IT directors would rather chew on glass than run their mission-critical applications on Windows servers. What is it about UNIX that keeps it going?

  • Hardware support and integration. Unlike other operating systems such as Linux or Windows, UNIX is typically packaged with vendor hardware and because the operating system has been optimized for a specific hardware platform, it offers performance and reliability advantages.
  • OS support. With UNIX operating systems, patches and fixes are all handled by the manufacturer of the specific brand of UNIX. You need not browse the Web to find the appropriate fix for your problem. On many occasions, phone support will direct you to the fix and even walk you through the installation. The operating system is supported by your vendor 24x7. When your box crashes (and every box crashes), there is always someone to call.
  • Comfort level. If you prefer working with a company that can hold your hand through all types of problems, UNIX is the answer for you. All UNIX vendors offer standard 24x7 contracts on both the hardware and the OS. The benefit here is that there is no finger pointing if something breaks, because the vendor supports both the hardware and the OS.
  • Security. UNIX is one of the most secure operating systems available.
  • Portability. UNIX runs on many different platforms. While it can be cumbersome to move to different flavors of UNIX, it is more an effect of how the hardware manufacturers have chosen to modify their UNIX flavors, which is less of a reflection on UNIX itself.
  • Reliability. UNIX is an extremely mature system, which just does not crash like other commercial operating systems such as Windows. While Linux is getting more mature, UNIX has almost 20 years on its little sister OS.
  • Hardware. UNIX systems run on very high-end powerful hardware, such as IBM's Power® platform. The performance is greater than on any other platform.

In a February 2009 report by International Data Corporation (IDC), the following was noted:

  • The UNIX market exhibited strong growth quarter over quarter with a revenue increase of 30.4% ($3,741M to $4,877M) and a unit increase of 8.3% (114,845 to 124,346).
  • UNIX was the largest OS segment by revenue last quarter, eclipsing Windows, which slipped to #2. Also on the processor front RISC systems themselves saw a 32.7% increase in revenue and a 15.3% increase in units shipped.

An April study showed even more. This IDC study on the UNIX market had UNIX at $69 billion in 2008, predicts UNIX $74 billion in 2013. The same IDC report shows The forecast says Linux-related software revenue will grow from $12 billion to $35 billion between 2008 and 2013. Furthermore, according to IDC, UNIX accounted for 36% of overall server market revenue in last year's fourth quarter.

Unquestionably, UNIX is very much alive. What about AIX?

Figure 1 shows the revenue growth of AIX over the past several years. At the close of 2008, IDC studies showed that IBM sold $6.4 billion worth of UNIX servers last year, for a 37.2% market share, while Sun's sales amounted to $4.8 billion, for a 28.1% share. Trailing behind in third place was Hewlett-Packard Co., with $4.6 billion in sales and a 26.5% market share. The trend itself has been consistent, starting in 2005. Gartner and IDC both ranked IBM as the market leader in the UNIX space.

Figure 1. AIX and Power System market position
market position

The history of AIX

AIX (Advanced Interactive eXecutive) is IBM's homegrown UNIX operating system. AIX was first introduced by IBM in 1986. IBM ported AIX to its RS/6000® platform in 1989. The release of AIX Version 3 coincided with the announcement of the first RS/6000 models. The unique factor of these systems were that they outperformed all other machines in integer-compute performance and also by a factor of 10 in floating-point performance.

Version 4 was introduced in 1994 and added support for symmetric multiprocessing (SMP) with the first RS/6000 SMP servers. The operating system continued to evolve until 1999, when AIX 4.3.3 introduced workload management (WLM). In May 2001, IBM unveiled AIX 5L, the L standing for "Linux affinity", which coincided with the release of its POWER4™ servers, which provided for the logical partitioning of servers. IBM created their first midrange hypervisor around this combination. More than any other factor, this was the breakthrough that IBM needed to challenge HP and SUN for UNIX supremacy. In just a few short years, IBM would dominate the market. In October of 2002, IBM announced dynamic logical partitioning (DLPAR) with AIX 5.2. AIX 5.3, introduced in August 2004, provided many new features: virtualization, security, reliability, systems management, and administration. Most importantly , AIX 5.3 fully supported the Advanced Power Virtualization (APV) capabilities of the POWER architecture; this included micropartioning, virtual I/O servers, and symmetric multithreading (SMT).

IBM introduced AIX 6.1 in November 2007. Some of its major innovations include workload partitions (WPARs), similar to Solaris containers, and Live Application Mobility (not available with Solaris), which lets you move these partitions without application down time. AIX was the first operating system to introduce the idea of a journaling file system (JFS), an advance that enabled fast boot times by avoiding the need to perform file system checking (fsck) for disks on reboot. AIX also has a strong built-in Logical Volume Manager (LVM), introduced as early as 1990, which helps to partition and administer groups of disks. Another important innovation was the introduction of shared libraries, which avoided the need for an application to statically link to the libraries it used. The resulting smaller binaries used less of the hardware RAM to run and required less disk space for installation.

Demonstrating their commitment to standards, the AIX OS was the first 64-bit UNIX OS to comply with the UNIX03 standard established by The Open Group and was the first operating system to support the UNIX 1998 standard. AIX has also included support for TCP/IP V6 since 1997, and was awarded the "Ready for IPv6" certification in 2006.

Figure 2 shows the historical timeline for the evolution of AIX.

Figure 2. The evolution of AIX

Power Systems and AIX -- The undisputed UNIX leader in 2010

AIX celebrated its own major anniversary, its 20th anniversary in January 2006, and it appears to have an extremely bright future in the UNIX space. IBM's AIX has been the only UNIX flavor that increased its market share through the years, and IBM continues to own the market space for UNIX servers. Most of the UNIX growth at this time stems from IBM. AIX has benefited from the many hardware innovations that the POWER platform has introduced through the continues to do so. It has also benefited from its virtualization engine - PowerVM™.

Why AIX? Performance, innovation, virtualization, availability, and a consistent roadmap

In a recent study on OS reliability, polling users from 27 countries, IBM's AIX led all server operating systems for downtime - approximately 30 minutes per server of downtime, per year. This has to do with AIX near Continuous Availability features.

During the early 1990's, there were five different RISC architectures that were actively competing with one another. IBM partnered with Apple and Motorola to come up with a common architecture, which would meet the standards of the alliance (A High-Performance Architecture with a History, 2006). Its first design was very simple and all instructions were completed in one clock cycle. It lacked floating point and parallel processing ability. The Power architecture was an attempt to correct this flaw. It consisted of over 100 instructions and was known as a complex RISC system. The Power1 chip consisted of 800,000 transistors per chip and was functional partitioned. It had separate floating point registers and could scale from the low- to the high-end workstations. The first chip actually had several chips on one single motherboard, but was refined to one RISC chip with more than 1 million transistors. It was used as the CPU for the Mars Pathfinder mission. While there were many other designs through the 1990's, it is true that the 1990's had mixed results for UNIX, as it lagged behind HP, Sun and other vendors.

IBM has made substantial improvements throughout the years on their IBM proprietary RISC-based hardware, where additional mainframe-type components are actually needed today to utilize the new architecture. Systems like the HMC (hardware management console) and the Hypervisor (software which runs on hardware machines and manages one or more operating systems) are important elements of the Power architecture.

The POWER5™ architecture, introduced in 2003, contained 276 million transistors per processor. It was based on the 130 nanometer copper/SOI Process and featured chip multiprocessing, a larger cache, a memory controller on the chip, simultaneous multi-threading (SMT), advanced power management, and improved hypervisor technology.

The POWER6®, with approximately 790 million transistors, debuted in June 2007. Its dual-core design enabled it to reach 4.7 GHz. Innovations in energy and cooling let it retain the same power consumption as the POWER5, while almost doubling performance. The POWER6 has hardware support for decimal arithmetic. It also has the first decimal floating-point unit integrated in silicon. Several important PowerVM Virtualization enhancements were also released with the POWER6, including Live Partition Mobility, Decimal Floating Point, and Dynamic Energy Management. The Power6 5.00 GHz processor, based on the Power 595 simply is the fastest system UNIX server in existence. The 64-core server outperforms the 128-core HP Integrity Superdome with more performance at one-half the amount of cores. The 595 also has 90% of the performance of the 256-core Sun SPARC Enterprise M9000 and 90% of the performance with one-quarter of the cores.

Power systems are based on mainframe-inspired reliability, availability, and serviceability (RAS) features such as First Failure Data Capture. This capability was also extended with introduction of the POWER6 processor-based servers to include Processor Instruction Retry, Alternate Processor Recovery, Partition Availability priority, Live Application Mobility, and Live Partition Mobility. All these features are designed to help enable you to eliminate systems-related planned and unplanned outages. If you need to take a system down for reconfiguration, firmware updates, or another reason, you will have the option of moving your applications to a different server without any impact to production operation. No reboots, no restarts, no service interruption, just continued outstanding service to your users.

How does AIX itself work with hardware to prevent outages? One example is storage keys. This new capability exploits the POWER6 hardware to provide additional isolation of kernel and application data. It prevents invalid changes to memory caused by programming errors. Application use of POWER6 storage keys are enabled in AIX 5.3 and the AIX kernel. The AIX kernel exploitation of POWER6 keys is included in AIX 6.1.

IBM is widely recognized as having the best virtualization product on the midrange, PowerVM. Some recent innovations include live application mobility (allowing one to fail over working partitions without downtime), Active Memory Sharing, and multiple shared processor pools. No other flavor of UNIX can boast these virtualization characteristics, nor can they match IBM's 40-year history of virtualization (PowerVM has evolved from mainframe/System z virtualization).

AIX runs only on IBM Power Systems, easily the most powerful of midrange UNIX servers. IBM sells the fact that AIX runs exclusively on Power as a plus because it is fully optimized on this architecture and it has a clear road map around which the company adheres to religiously. AIX has always had an integrated logical volume manager, unlike other flavors that require add-on products.


AIX is the only flavor of UNIX that has continued to grow market share in recent years, partly because of the capabilities of its Power hardware that continues to lead the field in reliability, availability, and scalability. It is clear that IBM is at the forefront of UNIX innovation today and unquestionably the future of UNIX stands to stay bright because of its flagship UNIX flavor, AIX.





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