Windows Server and Remote Desktop Services Licensing Basics
The best sources of Windows Server licensing info are Microsoft's licensing datasheets and Product Terms. This doc lists the most important aspects of licensing on-premise installations of Windows Server at UW-Madison.
Windows Server uses the server/client licensing model. In the server/client licensing model, both servers and clients connecting to the servers must be licensed.
All UW System faculty, staff, and students are licensed for client access to Windows Server under the terms of our Microsoft campus agreement, so in most cases you only have to purchase Windows Server licenses.
Windows Remote Desktop Services (RDS) also uses the server/client licensing model.
RDS servers are licensed with Windows Server; if you own a Windows Server license you're licensed to use an RDS server on the same machine.
RDS clients are not licensed, so if you want to use RDS, you have to purchase RDS user or device client access licenses (CALs) or external connector licenses.
The main difference between the Standard and Datacenter editions of Windows Server is virtualization rights. Datacenter allows for unlimited virtualization, while Standard has a limit of two VMs (you can license an additional two VMs in Standard edition by re-licensing the server; if you have more than a dozen or so VMs, licensing with Datacenter costs less).
In addition, these technologies are available in Datacenter but not in Standard:
Storage features including Storage Spaces Direct and Storage Replica
Shielded Virtual Machines
Software Assurance (SA)
The primary benefit of SA is to give you the right to upgrade to any version of the software released during the term of the SA (term as specified in the item description).
Additional Windows Server software assurance benefits include:
Use each Datacenter license on-premises and in Azure
Use each Standard license on premises or in Azure
How many licenses do I need to buy?
Windows Server licensing always references the physical cores (not processors, not CPUs, not virtual cores) of the machines being licensed.
Each of the Windows Server license SKUs available for purchase in the catalog licenses two cores in one physical server.
Microsoft enforces a minimum purchase of eight of the license SKUs per server, which licenses up to 16 cores in one machine. More cores would require additional purchases.
If you have Windows Server VMs running on multiple physical hosts, all of the cores in all of the physical hosts must be licensed.
However, if you can limit Windows Server VMs to specific hosts (using VMWare's VM-Host Affinity Rule or similar techology), you would only have to license the cores in the hosts to which the servers are restricted.
Since UW-Madison is already licensed for Windows Server CALs, you generally don't need to purchase CALs. If you want to license access by users unaffiliated with UW-Madison, you would buy an External Connector license to license one server for an unlimited number of external users.
CALs are required for each device or user. They are required regardless of the technology used to remotely access the server.
CALs are required for any device or user accessing any Remote Desktop Service, including but not limited to Remote Desktop Gateway, Remote Desktop Web Access, Remote Desktop Connection Broker, Remote Desktop Session Host, and/or Remote Desktop Virtualization Host.
One device CAL is required for each unique device accessing the server, not for the total number of devices at a given time.
One user CAL is required for each unique, named user accessing the server, not for the total number of users at a given time.
External Connector Licenses...
license access to Remote Desktop Services on one server by an unlimited number of users not employed by UW-Madison.
can be used to license students.
Windows Server and Remote Desktop Services licenses can be purchased from the Software Order Form.