what is ispostBack and how it work on page
when it execute or call

IsPostBack is a property of the Page that tells you whether or not the page is on its inital load or if a user has pressed a button on your WebForm that has caused the page to post back to itself.

General use is normally something like:
if(!Page.IsPostBack)
{
  //do something only the first time the page is loaded
}

This MSDN document will give you a better explination of this and the Page Lifecycle as a whole:

http://msdn.microsoft.com/en-us/library/ms178472.aspx

hth.
-Doug

================================================== =========
Read this if you want to know how to get a correct reply for your question:
http://www.catb.org/~esr/faqs/smart-questions.html
================================================== =========
.: Wrox Technical Editor / Author :.
Wrox Books 24 x 7
================================================== =========

IsPostBack is a property of the Asp.Net page that tells whether or not the page is on its initial load or if a user has perform a button on your web page that has caused the page to post back to itself To know more about http://net-informations.com/faq/asp/ispostback.htm asp.net ispostback

Yang