The values of controls of a particular page of the client browser is persisted by ViewState at the time of post back operation is done. If the user requests another page, the data of previous page is no longer available.
The data of a particular server persists in the server by SessionState. The availability of the user data is up to the completion of a session or closure of the browser.
A ViewState is a state of a page within a browser wherein the values of controls persist when post back operation is done. When another page is loaded, the previous page data is no longer available.
SessionState is the data of a user session and is maintained on the server side. This data available until user closes the browser or session time-outs.
