The IsPostBack property of the page object may be used to check whether the page request is a postback or not. IsPostBack property is of the type Boolean.
The Page_load event of the ASP.NET page life cycle assures that all controls are completely loaded. Even though the controls are also accessible in Page_Init event but here, the viewstate is incomplete.
Using HTML Hidden Fields, ASP.NET creates a hidden field with an ID=”__VIEWSTATE” and the value of the page’s viewstate is encoded (hashed) for security.
The ValidationSummary control in ASP.NET displays summary of all the current validation errors.
In case it is required for a server side control to postback when any of its event is triggered, then the AutoPostBack property of this control is set to true.
Web.config file is used to make the settings to a web application, whereas Machine.config file is used to make settings to all ASP.NET applications on a server(the server machine).
A session object can persist information between HTTP requests for a particular user, whereas an application object can be used globally for all the users.