在drupal上通过php上传文件

I am trying to get the user to upload a file and then save the file to the server using php. My code works on a non-drupal website but not on drupal. Here is my code:

<?php
  if ($_FILES["file"]["error"] > 0)
    {
    echo "Return Code: " . $_FILES["file"]["error"] . "<br>";
    }
  else
    {
    echo "Upload: " . $_FILES["file"]["name"] . "<br>";
    echo "Type: " . $_FILES["file"]["type"] . "<br>";
    echo "Size: " . ($_FILES["file"]["size"] / 1024) . " kB<br>";
    echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br>";

    if (file_exists("upload/" . $_FILES["file"]["name"]))
      {
      echo $_FILES["file"]["name"] . " already exists. ";
      }
    else
      {
      move_uploaded_file($_FILES["file"]["tmp_name"],
      "upload/" . $_FILES["file"]["name"]);
      echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
      }
    }
?>

On my non drupal site, I just create a folder called upload in the root directory and the files save to it no problem. In drupal, I created an upload folder in the sites/default/files/ directory and i can't find the file. The default is the file is supposed to be saved in the root folder but i can't find it, do you know where the file is being saved? Thanks.