Joomla! runs on the PHP pre-processor. PHP comes in many flavours, for a lot of operating systems. Beside PHP you will need a Web server. Joomla! is optimized for the Apache Web server, but it can run on different Web servers like Microsoft IIS.

From version 1.5.8x Joomla! requires PHP 5, this was due to a new JURI method--isInternal($url)— being introduced which addressed a security hole in previous versions.

The minimum version requirements are:

•    Apache 2.x,
•    PHP 5 or up
•    MySQL 5 or up

The JoomlaWired environment currently runs on the latest version of PHP and offers our client its added benefits, however If you have a PHP 4 site and concerned about security we urge you to update to PHP 5. If for some reason you can't, add this to the end of /libraries/joomla/utilities/compat/php50x.php

For the latest minimum requirements details visit the Joomla! Help Site and Forums.