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 libmysql. mysqlnd will be used to build the mysql, mysqli and PDO_MySQL extensions if libmysql isnt found on the system. It may also be used instead of libmysql even when libmysql is present. mysqlnd is recommended for all PHP installations for performance reasons.