Technology Stack Drupal 7

Drupal’s design goals include both being able to run well on inexpensive web hosting accounts and being able to scale up to massive distributed sites. The former goal means using the most popular technology, and the latter means careful, tight coding. Drupal’s technology stack is illustrated in Figure 1-1.

Figure 1-1. Drupal’s technology stack

The operating system is at such a low level in the stack that Drupal does not care much about it.
Drupal runs successfully on any operating system that supports PHP.

The web server most widely used with Drupal is Apache, though other web servers (including Microsoft IIS) may be used. Because of Drupal’s long history with Apache, Drupal ships with .htaccess files that secure the Drupal installation. Clean URLs—that is, those devoid of question marks,ampersands, or other strange characters—are achieved using Apache’s mod_rewrite component. 

This is particularly important because when migrating from another content management system or from static files, the URLs of the content need not change, and unchanging URIs are cool, according to Tim Berners-Lee (http://www.w3.org/Provider/Style/URI). Clean URLs are available on other web servers by using the web server’s URL rewriting capabilities.

Drupal interfaces with the next layer of the stack (the database) through a lightweight database abstraction layer, which was totally rewritten in Drupal 7. The database interface provides an API based on PHP data object (or PDO) and allows Drupal to support any database that supports PHP.  The most popular databases include MySQL and PostgreSQL. In Drupal 7, SQLite is now also supported. 

Drupal is written in PHP. All core Drupal code adheres to strict coding standards (http://drupal.org/nodes/318) and undergoes thorough review through the open source process. For Drupal, the easy learning curve of PHP means that there is a low barrier to entry for contributors who are just starting out, and the review process ensures this ease of access comes without sacrificing quality in the end product. And the feedback beginners receive from the community helps to improve their skills. For Drupal 7, the required version of PHP is 5.2.