What does IsPostBack actually mean?
<p>I am interested to know what specifically Page.IsPostBack means. I am fully aware of it's day to day use in a standard ASP.NET page, that it indicates that the user is 
submitting data back to the server side. See <a href="http://msdn.microsoft.com/en-us/library/system.web.ui.page.ispostback.aspx" rel="nofollow">Page:IsPostBack Property</a> </p>

<p>But given this HTML</p>

<pre><code>&lt;html&gt;
   &lt;body&gt;
      &lt;form method="post" action="default.aspx"&gt;
         &lt;input type="submit" value="submit" /&gt;
      &lt;/form&gt;
   &lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>When clicking on the Submit button, the pages Page_Load method is invoked, but the Page.IsPostBack is returning false. I don't want to add <code>runat=server</code>.</p>

<p>How do I tell the difference between the pages first load, and a Request caused by the client hitting submit?</p>

<p><strong>update</strong><br />
I've added in <code>&lt;input type="text" value="aa" name="ctrl" id="ctrl" /&gt;</code> so the Request.Form has an element, and Request.HTTPMethod is POST, but IsPostBack is still false?</p>
