PHP is an application language. It is not a server in its own right, nor is it a piece of software in the traditional sense. Nor is it a compiler like Pascal or C++. It needs to be installed wrapped, if you like in a Web server. With this in mind, for every installation of PHP, you will need some kind of Web server, such as Apache.
The phrase "installing PHP,'' therefore, is perhaps not quite accurate. The phrase "installing PHP and Apache'' would be better, but that misses the fact that PHP is heavily dependent on third-party libraries and applications for any of its more sophisticated functionality, such as libxml for XML parsing.
To make things worse, most applications that this book introduces you to, as well as anything useful you'll write yourself, require some kind of a backend database. In this book, we use PostgreSQL in preference to MySQL, but they are much the same in practice.
In fact, therefore, the actual steps for a PHP installation look something more like this:
Install and configure the various external libraries
Install and configure your database platform
Install and configure your Web server
Install and configure PHP
As you can see, it's far from child's play. To make matters a lot worse, the exact manner in which the preceding steps are accomplished varies, depending on your chosen operating system (UNIX or Windows), your chosen Web server (Apache, IIS, Zeus, and so forth) and your chosen database platform (MySQL, PostgreSQL, MS SQL Server, Oracle, IBM DB2, Informix).
To present the lowdown on every possible permutation in this appendix would not just have a huge impact on the number of trees required to produce this book, it would be madness, because there's a very convincing argument for one particular combination over all others.