Source Dell TechCenter global:
Microsoft Windows Server 2012 R2, is Microsoft’s latest version of Windows for Servers. This R2 release brings exciting new features and enhancements across virtualization, storage, networking, virtual desktop infrastructure, access and information protection, and more. Dell enables this operating system on a wide range of Server products. This document provides comprehensive details about important considerations for upgrading your server to Microsoft Windows Server 2012 R2.
You can download the pdf file here.