php spl_autoload_register vs __autoload?

hello is there any diffrence useing this excepts that we can use our own name auto load? is there any performance difference? how do they internally work?

between

function __autoload_libraries($class){
    include_once 'lib.'.$class.'.php';
}

spl_autoload_register('__autoload_libraries');

vs

function __autoload($class){
    include_once 'lib.'.$class.'.php';
}