Do TechNet em os requisitos mínimos absolutos para executar o Server 2012 R2 :
Be aware that 32 GB should be considered an absolute minimum value for successful installation. This minimum should allow you to install Windows Server 2012 R2 in Server Core mode, with the Web Services (IIS) server role. A server in Server Core mode is about 4 GB smaller than the same server in Server with a GUI mode. For the smallest possible installation footprint, start with a Server Core installation and then completely remove any server roles or features you do not need by using Features on Demand. For more information about Server Core and Minimal Server Interface modes, see Windows Server Installation Options.