title: What is a Partial Postback?
body: <p>I'm an experienced web developer in several different web technology stacks.  I currently work in .Net and I've become curious about the Partial Postback.</p>
  
  <p>I understand what the Partial Postback's function is and how to work with it programatically, but I don't like using technology that I don't understand, how is a Partial Postback implemented.</p>
  
  <p>I understand HTTP Requests and Asynchronous Requests, the thing that bugs me about the Partial Postback is that it seems to be both.</p>
  
  <p>Maybe I'm just missing something but it appears to me that the Partial Request does both, first firing off an Asynchronous POST Request but the Browser seems to be aware and the activity indicator starts to spin, which normally only occurs during an HTTP Request Page Render.</p>
  
  <p>So can anyone shed some light on how Microsoft implemented, at the HTTP Request level, the Partial Postback?</p>