PHP extensions are usually called "php_*.dll" (where the star represents the name of the extension) and they are located under the "PHP\ext" ("PHP\extensions" in PHP4) folder.
PHP ships with the extensions most useful to the majority of developers. They are called "core" extensions.
However, if you need functionnality not provided by any core extension, you may still be able to find one in PECL. The PHP Extension Community Library (PECL) is a repository for PHP Extensions, providing a directory of all known extensions and hosting facilities for downloading and development of PHP extensions.
If you have developped an extension for your own uses, you might want to think about hosting it on PECL so that others with the same needs can benefit from your time. A nice side effect is that you give them a good chance to give you feedback, (hopefully) thanks, bug reports and even fixes/patches. Before you submit your extension for hosting on PECL, please read http://pecl.php.net/package-new.php.
Many times, you will find several versions of each DLL:
You should keep in mind that your extension settings should match all the settings of the PHP executable you are using. The following PHP script will tell you all about your PHP settings:
<?php phpinfo(); ?>
Or from the command line, run:
The most common way to load a PHP extension is to include it in your php.ini configuration file. Please note that many extensions are already present in your php.ini and that you only need to remove the semicolon to activate them.
However, some webservers are confusing because they do not use the php.ini located alongside your PHP executable. To find out where your actual php.ini resides, look for its path in phpinfo():
Configuration File (php.ini) Path C:\WINDOWS
Loaded Configuration File C:\Program Files\PHP\5.2\php.ini
After activating an extension, save php.ini, restart the webserver and check phpinfo() again. The new extension should now have its own section.
If the extension does not appear in phpinfo(), you should check your logs to learn where the problem comes from.
If you are using PHP from the command line (CLI), the extension loading error can be read directly on screen.
If you are using PHP with a webserver, the location and format of the logs vary depending on your software. Please read your webserver documentation to locate the logs, as it does not have anything to do with PHP itself.
Common problems are the location of the DLL, the value of the " extension_dir" setting inside php.ini and compile-time setting mismatches.
If the problem lies in a compile-time setting mismatch, you probably didn't download the right DLL. Try downloading again the extension with the right settings. Again, phpinfo() can be of great help.