The system module is at the foundation of your Drupal website, and provides basic but extensible functionality for use by other modules and themes. Some integral elements of Drupal are contained in and managed by the system module, including caching, enabling or disabling of modules and themes, preparing and displaying the administrative page, and configuring fundamental site settings. A number of key system maintenance operations are also part of the system module.

The system module provides:

• support for enabling and disabling modules. Drupal comes packaged with a number of core modules; each module provides a discrete set of features and may be enabled depending on the needs of your site. A wide array of additional modules contributed by members of the Drupal community are available for download at the Drupal.org module page.
• support for enabling and disabling themes, which determine the design and presentation of your site. Drupal comes packaged with several core themes and additional contributed themes are available at the Drupal.org theme page.
• a robust caching system that allows the efficient re-use of previously-constructed web pages and web page components. Drupal stores the pages requested by anonymous users in a compressed format; depending on your site configuration and the amount of your web traffic tied to anonymous visitors, Drupal's caching system may significantly increase the speed of your site.
• a set of routine administrative operations that rely on a correctly-configured cron maintenance task to run automatically. A number of other modules, including the feed aggregator, and search also rely on cron maintenance tasks. For more information, see the online handbook entry for configuring cron jobs.
• basic configuration options for your site, including date and time settings, file system settings, clean URL support, site name and other information, and a site maintenance function for taking your site temporarily offline.

For more information, see the online handbook entry for System module.