When you use Server Manager to install the Web Server (IIS) role in Windows Server 2008 or 2008 R2, you are presented with roughly 40 role services to select from, relatively few of which are selected by default. Over time, you may add and remove services
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Read the complete post at http://blogs.iis.net/timamm/archive/2010/03/12/default-web-server-role-services-in-windows-server-2008-and-windows-server-2008-r2.aspx