PHP is the most popular web-development language in the world. According to esti-mates compiled in April 2004, there are over fifteen million unique domains—andalmost two million unique IPs—on the World Wide Web that reside on servers wherePHP is supported and used. The term “PHP” is actually a “recursive acronym” that stands for PHP: Hypertext Preprocessor. It might look a bit odd, but it is quite clever, if you think of it. PHP is a“scripting language”—a language intended for interpretation and execution rather thancompilation such as, for example, C. The fact that PHP is interpreted and not compiled, however, does not mean that it is incapable of meeting the demands of today’s highly intensive web environments—in fact,a properly written PHP script can deliver incredibly high performance and power.