Windows Server Standard
Built for physical or minimally virtualized environments. A single license includes rights to run up to two virtual machines (or one physical instance plus one virtual machine) on the licensed hardware.
Windows Server Datacenter
Designed for highly virtualized datacenters and software-defined environments. A Datacenter license grants unlimited virtual machine rights on the licensed hardware, plus Datacenter-only features like Storage Spaces Direct and Shielded Virtual Machines.
Core-based licensing and CALs
Both editions are licensed per physical core, with a minimum of 16 core licenses per server. Beyond the server license itself, each user or device accessing the server also needs a separate Client Access License (CAL).
Which edition do I need?
If you're running a handful of virtual machines on physical hardware, Standard is usually the more cost-effective choice. If you're running many VMs per host, Datacenter's unlimited virtualization rights pay for themselves.
