Windows Server 2012 brings our company’s experience building and operating public clouds to the server platform for private clouds. The new licensing and packaging makes it easier to manage workloads in highly virtualized public and private cloud environments. Windows Server 2012 will move to a consistent licensing model and will have common features enabling the reduction of editions.
Both Standard and Datacenter editions provide the same set of features; the only thing that differentiates the editions is the number of Virtual Machines (VMs). A Standard edition license will entitle you to run up to two VMs on up to two processors (subject to the VM use rights outlined in the Product Use Rights document).
A Datacenter edition license will entitle you to run an unlimited number of VMs on up to two processors.
All features that are available in the Datacenter edition are also available in the Standard edition, including high availability features like failover clustering. The only difference between the two editions will be virtualization rights.