PHP Version 3 can be installed in two primary ways: as an Apache module on Unix systems or as a CGI script on both Unix and Windows systems. See the installation instructions that come with PHP for full and current information.

When you are using PHP as an Apache module, PHP processing is triggered by a special MIME type. This is defined in the Apache configuration file with a line similar to:

AddType application/x-httpd-php3 .php3

This tells Apache to treat all files that end with the .php3 extension as PHP files, which means that any file with that extension is parsed for PHP tags. The actual extension is completely arbitrary and you are free to change it to whatever you wish to use.

If you are running PHP as a dynamic shared object (DSO) module, you also need this line in your Apache configuration file:

LoadModule php3_module
    modules/libphp3.so

When you are running PHP as a CGI script (with any web server), PHP processing is still triggered by this special MIME type, but a bit more work is needed. The web server needs to know that it has to redirect the request for the PHP MIME type to the CGI version of PHP. With ApacheNT, for example, this redirect is done with a set of configuration lines like the following:

ScriptAlias /php3/ "/path-to-php-dir/php.exe" 
AddType application/x-httpd-php3 .php3
Action application/x-httpd-php3 "/php3/php.exe"

For IIS, this redirect is set up through the Windows registry. Refer to the PHP installation instructions for full details.

At runtime, most aspects of PHP can be controlled with the php3.ini file (located in /usr/local/lib by default). For the Apache module version of PHP, this file is read only when the server is started or reinitialized. Changes to this file should be treated the same as changes to Apache’s own configuration files. In other words, if you make a change, you need to send your Apache server an HUB or a USR1 signal before the change will take effect.

Many aspects of PHP can also be controlled on a per-directory basis (or even per-location or per-request) when using the Apache module version. Most of the directives available in the php3.ini file are also available as native Apache directives. The name of a particular directive is the php3.ini name with “php3_” prepended. For a list of all available Apache directives, run your Apache httpd binary with the -h switch.