Does requesting $_SERVER variables need to query the server

This question will probably reveal my lacking knowledge of the fundamentals, but I'm a go for it anyway: When you use a $_SERVER variable, is a query made to the server to get the information or is it just sitting in a variable all ready to go? Reworded, is there any efficiency gained by storing the data in a "local" variable if it's going to be used many times in the script? My experience with jQuery has taught me to store $(objects) in local variables if they're going to be used repeatedly because the DOM is queried every time a jQuery object is generated, so I'm wondering if a similar logic applies. Example: if ($_SERVER['SCRIPT_NAME'] == 'how.php') // do stuff if ($_SERVER['SCRIPT_NAME'] == 'why.php') // do other stuff vs. $script_name = $_SERVER['SCRIPT_NAME']; if ($script_name == 'how.php') // do stuff if ($script_name == 'why.php') // do other stuff Cheerios, Marc