A language built for the web
PHP (PHP: Hypertext Preprocessor) started in 1995 as a set of Perl scripts for managing personal home pages. In five years it has evolved into the most widely used server-side language for generating dynamic web pages. With the release of version 4 in May 2000, PHP makes a significant architectural leap.
At the heart of PHP 4 is the new Zend Engine, the execution engine rewritten from scratch by Zeev Suraski and Andi Gutmans. Compared to the version 3 parser, the Zend Engine cleanly separates the parsing phase from the execution phase, delivering better performance and laying the groundwork for future optimisations. The result is a faster language capable of handling increasingly complex applications.
Key features
PHP 4 introduces several features relevant to web development:
- Native sessions: user state management across successive HTTP requests, without relying on external libraries
- Output buffering: control over the sequence in which data is sent to the client, useful for HTTP header manipulation and output compression
- Improved HTTP support: native handling of cookies, file uploads and HTTP authentication
- Database extensions: connectors for MySQL, PostgreSQL, Oracle, ODBC and other database systems
The request-response cycle
PHP’s execution model is inherently tied to the HTTP protocol. Each client request starts an interpreter instance: the script is loaded, compiled into intermediate opcode, executed, and the result is sent back as a response. When the request completes, memory is freed. This shared-nothing model has a structural advantage: every request is independent of every other, which simplifies horizontal scaling. Handling more traffic is a matter of adding servers.
The LAMP stack
PHP occupies the application layer of the LAMP stack: Linux as the operating system, Apache as the web server, MySQL as the relational database, PHP as the scripting language. This combination is entirely Open Source, with zero licence cost, and represents the infrastructure that runs the majority of dynamic websites. The integration between the four components is direct: Apache’s mod_php module executes PHP scripts within the web server process, eliminating the overhead of traditional CGI.
The LAMP stack has lowered the barrier to entry for web development, making it possible to build dynamic applications with accessible, well-documented tools.