In practice unix (small "u") is now a free operating system. Whilst the trademark Unix and the associated operating system is commercial and closed source, just like Microsoft Windows and many other operating systems, Unix clones --- hereafter unix --- abound and many of these are open source (free as in speech) or GPL'd (free as in speech and as in beer), and cost little or nothing to purchase and license.

Open Source and the GPL

There are several versions of free software. Two of the most notable are:

• Open Source Software, as promoted by the Open Source Initiative, and
• software distributed under the GNU General Public License (sic.) as developed and promoted by the Free Software Foundation (GNU).

Many commercial vendors are contributing to Open Source. Examples include:

XFS

This is a journalling file system developed by SGI.

Apple's Darwin (OS X)

The operating system underlying Apple's OS X has been released under a public licence. See this.

Advantages of Free Software

• Can add functionality.
• Insurance against being "held hostage" by proprietory OS providers.
• Facilitates debugging and trouble-shooting of applications.
• OS bugs are fixed much more quickly.
• No royalties to pay; no problems with licencing.

Cheaper (Free as in Beer)

There are several versions of unix available for free download, or the cost of media (e.g., CDs) plus postage-and-packing (and maybe a nominal fee of a few pounds) only. These are robust, stable O/S widely used by big companies for crucial and critical operations.

Those that I know of are mentioned below.

The Free Unices

• Linux, Linux Distributions include:
  • Debian
  • RedHat
  • SuSE
• FreeBSD
• OpenBSD
• NetBSD

Linux and Hardware Platforms

Linux is available for many hardware platforms: Sun/SPARC, SGI/MIPS, DEC?Compaq/Alpha, Apple/PowerPC, Apple/Motorola-68k, Intel and clones...

The Free Software Foundation (GNU)

The Free Software Foundation (GNU)... GNU