Obscure Branches on the UNIX Family Tree

Most everyone in the computer industry today is very familiar with the operating system Linux (or, as preferred by one of its effective creators, GNU+Linux). Many are also familiar with BSD, if only for its significance as a precursor to OS X. When you get to AIX, though, the branches of the UNIX tree get a lot shakier. In this article, we’ll look at some basic history of UNIX and UNIX-like operating systems, and then look at some lesser-known (at least in academic environments) UNIX-like operating systems.

UNIX (generically ‘Unix’, although I refer to the trademark name and, hey, all-caps looks cooler anyway) was originally developed at Bell Labs by the major cast of Bell Labs computer researchers: Ken Thompson, Dennis Ritchie, Brian Kernighan, etc. Calling them the “usual cast” here is a bit of a joke, as they are so well-known as a group specifically because of the work they did on UNIX and closely-related projects including the C programming language.

UNIX development began at the very end of the ’60s and was based heavily on the MULTICS operating system – indeed, the name “UNIX” was a spelling simplification of “UNICS,” which was simply a pin on MULTICS. MULTICS was a fairly short-lived operating system developed by MIT, Bell Labs, and GE. Today it’s entirely forgotten, except for the fact that many of the significant features in UNIX (including elements of the “UNIX Philosophy”) actually originated with MULTICS several years earlier. In any case, UNIX was a significant improvement over MULTICS in many practical ways, including a significantly simplified and more maintainable codebase (indeed, concerns about the maintainability of the MULTICS code were what killed the project).

A lot of people don’t realize that UNIX did not evolve directly with C. UNIX was actually originally written in assembly and was rewritten in C several years later, in 1973. This change was of course rather revolutionary for the operating system as it made it highly portable, and encouraged use of UNIX on a wide variety of machines, not just a couple of IBM and DEC architectures used within Bell Labs.

UNIX really found its modern influence, though, when Bell Labs started licensing it to universities for academic use. Because of its power and portability, UNIX quickly became very popular in academic computing and a huge number of universities took advantage of its distribution in source-code form to produce modifications and improvements of UNIX for local use. This lead to one of the most important UNIX variants when UC Berkeley started distributing the Berkeley Software Distribution (BSD) in 1978.

Development of UNIX continued at Bell Labs and culminated with the release of System V, often referred to as SysV. Starting in 1983, SysV was sold commercially on a large scale to business users, and cemented UNIX as a sound choice for business computing.

So, this brings us to the well-known UNIX variants of the modern day. BSD is (one of) the precursors to Darwin which is the core of OS X, and research UNIX was the basis of MINIX which lead Linus Torvalds to work on Linux. These two operating systems are in everyday use today, and to a lesser extent BSD itself is also used today, particularly in networking applications. SysV is known by many for having been the source of a number of components of the GNU+Linux system, most obviously SysVinit.

But that’s not the only thing that SysV left us. SysV’s popularity in business led to multiple SysV-based operating systems that continue in use in the business environment to this day, often under the hood and away from public view. They’re not particularly sexy, but there’s a good chance that your bank uses them. Let’s look at the Big 3: HP-UX, IBM AIX, and Solaris. I’ll put special emphasis on why you might still use these operating systems, even though it’s 2016.

HP-UX is a System V based operating system first released by Hewlett Packard in 1984. HP-UX came into the market mostly via HP 9000-series computers (of various RISC-like architectures), which were used as both workstations and servers in the late ’80s and lived on for quite a while before being replaced entirely by Itanium-based machines. Modern HP-UX is built only for Intel Itanium, and takes advantage of the IA-64 architecture to offer a number of “enterprise” features, most notably operating-system virtualization, essentially containerization with hardware isolation. HP-UX is typically run on the comically named “SuperDome” line, currently lead by the HP Integrity SuperDome 2. The SuperDome is modular, offering hot-swap of almost all hardware to minimize downtime for repairs. It essentially competes in the modern mainframe space, as a heavyweight “vertically scaled” solution for critical applications.

HP-UX’s most important historical contribution was the addition of ACLs to the standard UNIX permission system, which it offered before any other UNIX-based operating system. This lead naturally to HP-UX’s modern niche of providing exceptionally strong isolation of virtual containers.

IBM had some involvement with UNIX for most of its lifetime, but only stepped into the UNIX market itself in 1985 with the IX/370 operating system for System/370. From this point on, IBM often offered UNIX-like operating systems for its computer solutions, including the IBM PC. The most durable of their UNIX descendents, though, was AIX, originally developed for workstations and later ported for mainframes as well. AIX did not become particularly significant, though, until it was ported for the IBM POWER architecture in 1990.

IBM POWER, now POWER8, is a modern PowerPC line that offers a number of advanced features. AIX takes advantage of these to improve performance and to offer LPAR, IBM’s hardware partitioning system. LPAR can be viewed as a container virtualization strategy baked into the hardware at a very low level, with almost perfect isolation between LPARs and flexible resource allocation. LPARs running on the same machine are considered equivalent to physically separate machines, even for virtually all security purposes, a feat that very few computer systems can achieve.

Solaris is perhaps the best known of these three in academic environments. Solaris was created by Sun Microsystems based on System V (which they had actually contributed to). The naming history is actually a bit confusing, as the operating system was marketed as SunOS until SunOS 5 was renamed to Solaris 2. This made previous SunOS releases Solaris 1, and both names can be used for them. Solaris 2 – the first “real” version of Solaris – came out in 1991, making it the newest of these UNIX variants.

Solaris was originally popular on the SPARC architecture, which was based on RISC and enjoyed wide popularity on both workstations and servers in the early to mid ’90s. SPARC processors remain available today, and in fact recently saw a significant architecture update, but SPARC is forgotten in most industries. The current stronghold of SPARC is in HPC, with a number of highly-ranked supercomputers having some SPARC component. Solaris s still updated today as well, although it is perhaps now better known for its open-source derivative illumos, which is popular particularly for storage systems.

The most important connecting thread of these three modern UNIX derivatives is that they are all based directly on System V. System V has an enormous legacy in business computing and played a big part in enabling much of the infrastructure that we use today – and like most elements of computer history, it just won’t quite die. Most of these distributions have maintained a niche by focusing on high-performance and high-reliability virtualization, an application that I call “the modern mainframe” and is attractive to many large businesses that want a high-reliability virtualized platform without the engineering overhead of a horizontal scaling or redundancy approach.

These sorts of applications are often described as ‘enterprise,’ and ‘enterprise’ is often used as a pejorative for a reason. These operating systems tend to be high cost and evolve slowly. In the end, I suspect that they are on their last legs. There’s a long tail and we’ll see them around for years to come, but Linux, Windows, and OS X have captured the market to such an extent that there isn’t a lot of room left for anything else in serious usage.

  • history/computers/obscureunix.txt
  • Last modified: 2020/11/16 23:46
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