Windows Server System Reference Architecture

Windows Server System Reference Architecture empowers systems integrators and IT professionals with validated architectural guidance that establishes the Microsoft platform as the most trustworthy platform for business computing. The reference architecture enables best practice-based design of an IT infrastructure, which drives standardization across the platform by applying sound architectural principles around security, manageability and other factors to ensure a consistent approach to the definition of IT services.

http://www.microsoft.com/technet/itsolutions/wssra/raguide/default.mspx