public static function bytes($bytes)
  {
    $kbytes = sprintf("%.02f", $bytes/1024);
    $mbytes = sprintf("%.02f", $kbytes/1024);
    $gbytes = sprintf("%.02f", $mbytes/1024);
    $tbytes = sprintf("%.02f", $gbytes/1024);

    if($tbytes >= 1)
      return $tbytes . " TB";
    if($gbytes >= 1)
      return $gbytes . " GB";
    if($mbytes >= 1)
      return $mbytes . " MB";
    if($kbytes >= 1)
      return $kbytes . " KB";

    return $bytes . " B";
  }