Windows Server 2016 is the cloud-ready operating system that delivers new layers of security and Azure-inspired innovation for the applications and infrastructure that power your business.
Windows Server 2012 and Windows Server 2012 R2 brings our experience delivering global-scale cloud services into your infrastructure with features and enhancements in virtualization, management, storage, networking, virtual desktop infrastructure, access and information protection, and the web and application platform.
For more information, go to https://technet.microsoft.com/library/hh801901.aspx
Windows Server 2008 R2 and Windows Server 2008 is the first 64-bit-only operating system released from Microsoft. Version enhancements include new functionality for Active Directory, new virtualization and management features, version 7.5 of Microsoft IIS Web Server and support for up to 256 logical processors. When deployed in a file server role, new File Classification Infrastructure services allow files to be stored on designated servers in the enterprise based on business naming conventions, relevance to business processes and overall corporate policies.
For more information, go to https://technet.microsoft.com/library/dd349801
Supported Operating Systems for Dell PowerEdge System playlist on YouTube