By choosing the operating system at this stage, you have eliminated a number of Web server choices in particular, IIS, which has never made it to the UNIX platform (perhaps unsurprisingly). You are left with a number of choices on UNIX Apache, Zeus, AOL Server, and Pi3Web.
There are two main manners in which PHP can be compiled and installed: as a CGI executable or as an integral part of the Web server, known as a SAPI module. The latter of these is a great deal faster and can handle many more concurrent connections. A CGI binary requires an instance of the PHP interpreter to load with every single HTTP request, which is very inefficient. All the previous choices stated support PHP as a SAPI module.
The previous choices are all perfectly valid, but so prevalent is the Apache server that it is practically unavoidable. It is running on something like 70 percent of the world's Web servers. Picking up from our earlier argument, the ISPs to whom you will be deploying will almost certainly be running Apache in preference to any of the other alternatives. You will make your life considerably easier if you stick to Apache.
It's a good choice in its own right, too. Apache has proven to be stable, secure and very well supported; also, it is constantly being further developed.
Also interesting to note is that at the time of this writing, AOL Server's own Web site at www.aolserver.com isn't running AOL Server; it's running Apache.
With all this in mind, the instructions in this section relate to getting PHP up and running on Apache on UNIX. Thankfully, the Web server in use, in contrast to the operating system, doesn't really affect PHP syntax at all, so the examples in this book, although they may be specific to UNIX, aren't specific to any particular Web server.