Difference Between PostBack and Call Back

Callback send a request to the web page from the client script. A client side function will send request to the server and a marked method is invoked on the
server. It does the processing on the server and returns the result back to the client. To enable client side callbacks, ICallbackEventHandler interface needs to be used and one need to implement RaiseCallBackEvent & GetCallBackResult function.

Where Postback sends the form data to the server. The server processes the data and sends it back to the browser. The page goes through its full life cycle and is rendered on the browser.

Callback does not redraw the page where postback does.