Every AspDotNet form has a hidden field that stores all the view state of the form.
<input type="hidden" name="__VIEWSTATE" value="dDwtMTE1MTIwMDUz" />
Actually, it is much much longer
This view is represented by StateBag object.
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The ViewState variable is a Base64 representation of a serialization of the StateBag, so the larger the page's objects, the longer the ViewState. --AllanBaruz