How Update Panel Works?

Update panel is used quite often for doing partial post back.
Here is look on how this happens behind the scenes using Update panel.

Update is panel is always used in conjunction with Script Manager.
Script manager is the component which basically allows partial rendering of the content, registering all the components required for asynchronous calls.

Now coming to Update panel.
If we place a control inside an update panel then it will trigger the partial  post back and only the controls which are inside the same update panel or other update panel for which trigger is defined is updated.

If we look at the request header that is sent to server using fiddler is (see the highlighted text)

With this type of header information Script manager on the server side knows which control has caused the post back and prepares the differential response of all the controls being updated.
the possible response looks like:

Now at the client side client run time gets this response and renders the same to parts which are need to be updated.


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