title: How does session_start know, whether to resume or start the session?
body: <p>I don't exactly understand how does <code>session_start</code> work ? For example, here is a script named :</p>
  
  <p>tester.php</p>
  
  <pre><code>&lt;html&gt;
   &lt;body&gt; &lt;head&gt; &lt;title&gt; tester.php &lt;/title&gt; &lt;/head&gt;
  
     &lt;?php
       session_start();
       $_SESSION['Mir Taqi Mir'] = "Dekh toh dil ke jaan se uthta hai,yeh dhuan sa kahaan se uthta hai";
     ?&gt;
  
     &lt;a href='./try.php'&gt;Click to follow&lt;/a&gt;
  
   &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>and a script named <code>try.php</code> :</p>
  
  <pre><code>session_start();
  
  if(isset($_SESSION['Mir Taqi Mir']))
   {
     echo "Value of the session variable :".$_SESSION['Mir Taqi Mir'];
   }
  </code></pre>
  
  <p>When I follow down to <code>try.php</code> from <code>tester.php</code> how does <code>session_start</code> know that it has to resume a session and not start a new session ?</p>
  
  <p>The <a href="http://php.net/manual/en/function.session-start.php" rel="nofollow">documentation</a> states : <code>session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.</code> What identifier ? I do not understand this.</p>