It might be said that the Unix market enjoys competition, but it could also be said that the Unix market suffers from competition. The problem has been that individual vendors have created their own versions of Unix that are incompatible with all other versions. This means that a binary executable for one version is usually incapable of running on any other Unix, even if the hardware is identical.
The problem is gradually being solved by several forces. First, the SVR4 standard has become dominant. An old joke goes that Sun succeeded in uniting the Unix industry, but unfortunately it united the industry in a coalition against Sun. Nonetheless, SVR4 is now the de facto standard. Programs written to the SVR4 standard have source-level portability to other SVR4 systems, meaning that you should be able to recompile the code for each system without changes. Second, the increasing popularity of Sun Microsystems’ Solaris implementation of SVR4 means that Solaris is becoming the de facto standard for binary-level portability, while the future of most other versions of Unix is in doubt, with the exception of Linux (which is not Unix in a legal sense). Finally, as more applications are written in Java, small differences between operating systems will become irrelevant. Systems will be forced to compete on performance and cost, not compatibility.
In the following sections we’ll go over the major versions of Unix used for web serving.
Solaris is Sun Microsystems’ ...