There are a lot of questions that arise for customers who want to install Microsoft  Exchange on their current Windows Server 2008 R2.  Cheng Pei Koay, a Microsoft Premier Field Engineer, provides us with a quick and handy table which maps the supported Exchange versions to the required Windows Server Operating System, along with information on the kinds of errors that may occur if versioning isn't considered.  Check it out at http://www.opsvault.com/microsoft-exchange-which-windows-server-operating-system-is-required/.