You can access System Info by clicking on 'System Info' in the 'Help' menu on the back-end of your Joomla! installation.
The System Info screens provides useful information about your host server environment, including operating system, PHP settings, and directory access settings. This information is very helpful when you are troubleshooting setup problems. Note that none of these settings can be changed from these screens. That must be done in other places.
These is the Relevant PHP Settings information (originally under the System Info tab of Joomla! 1.0) which are the general access and configuration requirements of specific PHP settings. If any of these is highlighted as incorrect should be taken care of to rectify the situation.
Originally under the System Info tab of Joomla! 1.0, this is the content of the current Joomla! configuration.php file which is stored under the main joomla_root/ directory. This file is created for you automatically when you first installed Joomla! and where most changes of the Global Configuration section of Joomla! are recorded. Please note that none of the settings can be changed from this page.
Originally labeled as Permissions in Joomla! 1.0, this shows you a list of directories the webserver should have write access to. Please note that all directories listed on this page should say Writable, action would be needed if they're not writable.
The PHP Info Tab is the output of an integrated php.info script built into Joomla!. It displays the full configuration of the PHP server side scripting language that Joomla! runs on, together with all the associated system information that goes towards the creation of the web server.
PHP is installed, and runs on the server (hence the server side above), and therefore all the settings are made on the server. The visitor to the web site does not need to have anything special running on their local machine in order to view/use any of the extra functionality that PHP gives to the web site.
All the settings that are ever likely to be needed are displayed here. Any changes that are required would be made within the php.ini and other files on the web server.
How much control a web site owner has over this information depends on whether they own the server or if the server host is flexible in their customer approach.
It is a good practice to know the limitations of a particular server installation and this screens output is key to that information gathering operation.
For full details on the information contained within the PHP Info screen visit: http://php.net/phpinfo.
These screens are display-only - none of the settings displayed on these screens can be changed here. The configuration file can be changed from the Global Configuration screen, all other settings are dependent on your host server configuration, and cannot be changed from inside Joomla!