Windows Server 2003 R2 Datacenter Edition will allow you to run an unlimited number of virtual instances of Windows Server on processors, which simplifies licensing and lowers the cost of Windows Server for large-scale virtualization. Windows Server 2003 R2 Enterprise Edition (EE) will allow you to run up to four virtual instances of Windows Server 2003 R2 EE on one licensed physical server or hardware partition, thereby decreasing the costs of server virtualization.