The following new extensions are added (by default) as of PHP 5.3.0:
mysqlnd is a new core library shipped with PHP. It is a PHP-specific replacement for libmysqlclient. mysqlnd will be used to build the mysql, mysqli and PDO_MySQL extensions if libmysqlclient isn't found on the system. It may also be used instead of libmysqlclient even when libmysqlclient is present. mysqlnd is recommended for all PHP installations for performance reasons.