SharePoint controls are not new to SharePoint 2010 master pages; SharePoint 2007 master pages included a number of controls for managing functionality across SharePoint pages and sites. However, there are a number of new controls introduced in 2010, including controls relating to AJAX and ribbon functionality. When creating new SharePoint 2010 master pages you must include the following controls:
<SharePoint:SPPageManager> is located inside the
<head> tag. It manages communications on pages between server ribbon, toolbars, and other controls on the page.
<SharePoint:ScriptManager> is located in the
<SharePoint:ScriptLink> is located ...