ScriptManager

This ScriptManager control is mandatory for every page using AJAX and every page should have only one ScriptManager control.In some cases when we use user controls that use AJAX functionalities and the calling page also uses Ajax functionalies, there will be multiple ScriptManager controls for that page and will create error.To overcome that difficulty,Microsoft gives ScriptManagerProxy control which we can use whenever we need multiple ScriptManager Controls.
Functionality of ScripyManager Control:
The ScriptManager control is central to AJAX functionality in ASP.NET. The control manages all ASP.NET AJAX resources on a page. This includes downloading Microsoft AJAX Library scripts to the browser and coordinating partial-page updates that are enabled by using UpdatePanel controls. In addition, the ScriptManager control enables you to do the following:Register script that is compatible with partial-page updates. In order to manage dependencies between your script and the core library, any script that you register is loaded after the Microsoft AJAX Library script.Specify whether release or debug scripts are sent to the browser.Provide access to Web service methods from script by registering Web services with the ScriptManager control.Provide access to ASP.NET authentication, role, and profile application services from client script by registering these services with the ScriptManager control.Enable culture-specific display of ECMAScript (JavaScript) Date, Number, and String functions in the browser.Access localization resources for embedded script files or for stand-alone script files by using the ResourceUICultures property of the ScriptReference control.Register server controls that implement the IExtenderControl or IScriptControl interfaces with the ScriptManager control so that script required by client components and behaviors is rendered.

Syntax for ScriptManager:

Syntax for ScriptManagerProxy: