what is this windows server 2012?
It is the fifth version of the Windows Server operating system by Microsoft, as part of the Windows NT family of operating systems.
Windows Server 2012
Windows Server 2012 is the fifth version of the Windows Server operating system by Microsoft, as part of the Windows NT family of operating systems. It is the server version of Windows based on Windows 8 and succeeds Windows 7-based Windows Server 2008 R2, released two years prior. 
windows server 2012 r2 datacenter vs windows server 2012 r2 standard UNANSWERABLE
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Windows Server 2012 [SEP] Introduction
Windows Server 2012 is the fifth version of the Windows Server operating system by Microsoft, as part of the Windows NT family of operating systems. It is the server version of Windows based on Windows 8 and succeeds Windows 7-based Windows Server 2008 R2, released two years prior. Two pre-release versions, a developer preview and a beta version, were released during development. The software was generally available to customers starting on September 4, 2012, by Microsoft. A successor was released on October 18, 2013, entitled Windows Server 2012 R2. Microsoft will end its extended support for Windows Server 2012 on October 10, 2023.