PHP, difference between $_SERVER['SERVER_NAME'] and $_SERVER['HTTP_HOST']

In PHP, $_SERVER['SERVER_NAME']  refers to the name of the server host.
$_SERVER['HTTP_HOST']: Contents of the Host.
Look at the following code at http://localhost:8083/test..php
  <?php
echo($_SERVER['SERVER_NAME']).'<br />';
echo($_SERVER['HTTP_HOST']);
?>
$_SERVER['SERVER_NAME'] returns localhost, while  $_SERVER['HTTP_HOST'] returns localhost:8083.
When we use the web server with a port , we had better  use $_SERVER['HTTP_HOST'] instead of $_SERVER['SERVER_NAME'] to return correct  web address in PHP.