What is it?
A 30 year old industrial-strength operating system, scalable from single-user workstations up to mainframe-sized servers supporting thousands of users. For nearly two decades Unix has been the operating system favoured by Microsoft's competitors. Linux, the current not-from-Microsoft choice, is a variant of Unix.
Where did it originate?
At AT&T's Labs in the late 1960s and early 1970s. Unix began with the effort to create an interactive, multi-user operating system that would not be tied to any supplier's hardware.
It gained momentum when Bell Lab's management objected to the developers running a computer game called Space Travel on the mainframe. They found an under-used Dec PDP7, and ported it to that. When the fledgling operating system was moved to a PDP11, the management were interested enough to pay for the hardware.
Unix creator Ken Thompson took a six-month sabbatical as visiting professor at the University of California's Berkeley campus. The resulting Berkeley Software Distribution (BSD) became one of the most important Unix variants.
Universities could license Unix for a nominal fee, leading to widespread use among students. Graduates then took it with them into the commercial world.
What's it for?
Mid-range systems, since it provides much of the reliability and functionality of mainframes at a fraction of the cost, together with a scalability and robustness that Windows has only just begun to deliver.
What makes it special?
Multi-user and multi-tasking capability, and portability between different hardware architectures.
How difficult is it?
Where Windows was developed from a quick-and-dirty end-user operating system (QDos) by college drop-outs, Unix was painstakingly assembled by computer scientists who were relatively free from commercial pressures. Unix can therefore seem daunting to people who grew up with the free-and-easy approach Microsoft fosters. However, once you have got to grips with the fundamental concepts - the kernel, the shell and the tools - you should be able to work with any version of Unix.
Where is it used?
Unix is strongest in research and development and education, in manufacturing, electronic engineering, telecoms and defence, although it is also widely used for general business applications. Sun's version, Solaris, is favoured by many Internet service providers.
Not to be confused with
The name Unix is also used for a Mexican brand of nappies, a Japanese version of Tupperware, a Spanish fire extinguisher and a French fungicide.
What does it run on?
Sun (Solaris), IBM (AIX), Hewlett Packard (HP-UX) and Compaq (Tru64) are the leaders. According to industry analyst IDC, Sun has 28.8% of the Unix server market, HP has 28.5% and IBM has 20.9%.
Few people know that
In 1992, the AT&T-owned Unix System Laboratories sued over BSD's claims to be Unix. Similarly, in the late 1980s, two organisations - the Open Systems Foundation and Unix International - claimed to offer an open, supplier-independent Unix. The resulting "Unix wars" reinforced the view that the Unix community was riven by factions and incompatible versions.
What's coming up?
Not a lot. The IBM-driven Monterey project to port AIX/Unixware to Intel's 64-bit Itanium chip, and Sun's efforts to do the same with Solaris, have both been canned.