Installation of extensions on Windows After installing PHP and a web server on Windows, you will probably want to install some extensions for added functionality. You can choose which extensions you would like to load when PHP starts by modifying your php.ini . You can also load a module dynamically in your script using dl() . The DLLs for PHP extensions are prefixed with php_ . Many extensions are built into the Windows version of PHP. This means additional DLL files, and the extension directive, are not used to load these extensions. The Windows PHP Extensions table lists extensions that require, or used to require, additional PHP DLL files. Here's a list of built in extensions: // change the following line from ... ;extension=php_bz2.dll // ... to extension=php_bz2.dll Some of the extensions need extra DLLs to work. Couple of them can be found in the distribution package, in the C:\php\dlls\ folder in PHP 4 or in the main folder in PHP 5, but some, for example Oracle ( php_oci8.dll ) require DLLs which are not bundled with the distribution package. If you are installing PHP 4, copy the bundled DLLs from C:\php\dlls folder to the main C:\php folder. Don't forget to include C:\php in the system PATH (this process is explained in a separate FAQ entry ). Some of these DLLs are not bundled with the PHP distribution. See each extensions documentation page for details. Also, read the manual section titled Installation of PECL extensions for details on PECL .