The following code includes a function to calculate the total hard disk space taken up by a directory.

<?php

$totalsize=0;

function show_dir($dir, $pos=2){
   global $totalsize;
   if($pos == 2)
      echo "<hr><pre>";

   $handle = @opendir($dir);
   while ($file = @readdir ($handle)){
      if (eregi("^\.{1,2}$",$file))
         continue;
      if (is_dir($dir.$file)) {
         echo "|- ".$pos."s <b>$file</b>\n";
         show_dir("$dir.$file/", $pos+3);
      } else {
         $size=filesize($dir.$file);
         echo "|- ".$pos."s $file ";
         echo("$size <br>");
         $totalsize=$totalsize+$size;
      }
   }
   @closedir($handle);

    if($pos == 2) echo "</pre><hr>";
    return($totalsize);
}

$totalsize = show_dir("c:/winnt/system32/");
echo($totalsize);
?>