Viewstate is stored in hidden input field and sent back to 
the server with every post back.
veiwstate is a concept of maintaing the controls props.
adv: 
redusing the manuel coding
it can not use persistant memory in client system or server 
system.
dis adv:
more amount of data can be transfered between client and 
web server
configaration :
we can figure viewstate at three levels
1.pagelevel
2.control level
3.application level
      cl:<input.......... enableviewstate="true[d]/false">
      pl:<%@page...........enableviewstate="tr true
[d]/false"%>
      al:this is required configurationfile
            <pages .......... enableviewstate="true
[d]/false>