Although some of the newer, built-in server application functions in Windows Server 2008 R2—such as Network Policy Server, server virtualization, Remote Desktop Services Web Access, Media Server, and so on—provide key areas for organizations to select as initial areas to implement Windows Server 2008 R2 technologies, other organizations might find add-in applications as being the key areas that drive an initial implementation of Windows Server 2008 R2. Some of the add-in applications come from Microsoft, such as the Microsoft Exchange Server 2010 messaging system or Microsoft SQL Server 2008 database system. Other add-ins to Windows Server 2008 R2 are provided by companies that provide human resource management applications; accounting software; document management tools; fax or voicemail add-ins; or other business, industry, or user productivity capabilities.
In earlier Windows Server operating systems, the core operating system provided simple logon and network connectivity functions; however, with Windows Server 2008 R2, the operating system includes many core capabilities built in to the Windows Server 2008 R2 operating environment. With integrated fault tolerance, data recovery, server security, remote access connectivity, web access technologies, and similar capabilities, organizations creating add-ins to Windows Server 2008 R2 can focus on business functions and capabilities, not on core infrastructure reliability, security, and mobile access functionality. This off-loading of the requirement of third-party add-in organizations to implement basic networking technologies into their applications enables these developers to focus on improving the business productivity and functionality of their applications. Additionally, consolidating information routing, security, remote management, and so on into the core operating system provides a common method of communication, authentication, and access to users without having to load up special drivers, add-ins, or tools to support each and every new application.
Much of the shift from application-focused infrastructure components to core operating system-focused functionality was built in to Windows 2000 and then later enhanced in Windows 2003 and Windows Server 2008. There were many challenges to earlier versions of the Windows operating system; however, after being on the market for many years now, Windows Server 2008 R2 add-ins have had several revisions to work through system functionality and component reliability between application and operating system. Fortunately, Windows Server 2008 R2 uses the same application/operating system technology used in Windows 2003 and Windows Server 2008, so applications written for Windows 2003 and Windows Server 2008 typically need just a simple service pack update to be able to run on Windows Server 2008 R2, if anything at all.
Source of Information : Sams - Windows Server 2008 R2 Unleashed