Windows Server billing is based on the number of physical cores in the servers in combination with Client Access Licenses (CALs) for the users.
Core licenses for the servers
Windows Server licenses are assigned to physical servers, based on the physical cores in the CPUs. A license is assigned to each core. Each physical CPU (socket) gets a minimum of eight core licenses assigned and each physical server a minimum of 16 core licenses. Even if the server has fewer physical cores.
Datacenter licenses may also cover Standard installations. The other way around is not allowed.
Software Assurance entitles you to new versions, use of disaster recovery servers, use of servers in Azure (Hybrid Benefit), support and Self-hosting.
Windows Server 2012 (R2) licenses are licenses for two physical CPUs. Older licenses are licenses per physical server.
For each set of Standard core licenses that cover all physical cores, up to two Windows Standard or Enterprise VMs can run on that physical machine. If all cores are assigned two licenses, four VMs can run on them. And so on. Standard licenses are useful for machines with few or no VMs.
If Datacenter licenses are assigned to all physical cores, an unlimited number of VMs can run on that physical server with Windows Standard, Enterprise or Datacenter installations. This option is useful for machines with many VMs, such as in local data centers.
Core Infrastructure Server (CIS) Suite
The Core Infrastructure Server Suite is a combination of Windows Server and System Center for servers. These licenses cost slightly less than the sum of Windows Server and System Center licenses. The license assignment and terms are the same as for Windows Server.
Client Access Licenses (CALs)
Licenses are also required on the user side. These can be licenses per user or licenses per end user device (PC, laptop, Thin Client ...).
A per user CAL allows a user to use an unlimited number of devices to access an unlimited number of Windows Servers. A per device CAL allows an unlimited number of users to access an unlimited number of Windows Servers via the licensed device.
Windows CALs are part of the Core CAL Suite and the Enterprise CAL Suite. These suites are available on a per-user and per-device basis.
The Microsoft Enterprise Mobility & Security (EMS) Suite includes a “Windows CAL Equivalent License”. Just like a Windows Server CAL, this right entitles you to access Windows Server. The EMS license is only available per user.
External Connector licenses
External users who have access to the Windows Servers or to applications running on Windows Server also need CALs. You do not need a CAL if it concerns unauthenticated use via the internet. For example, if an external person views a website and does not log in via Windows Server, or via an application running on it.
To avoid having to pay many CALs in some situations, the External Connector license is an alternative. This license is assigned to a physical server and covers external use of the physical server and of any virtual servers running on it. This license is required for every physical server that facilitates external use. It is also possible to assign external users a CAL or to use a mix of both options.
CALs for additional functionality
In addition to CALs for using Windows Server functionality, there are also CALs for specific additional functionality. These CALs are in addition to the regular Windows CALs.
- Windows Server Remote Desktop Services (RDS) CAL. Required to use remote desktop services and to use a graphical interface hosted by a Windows Server. Available per user and per device. An External Connector license is available for external users.
- Windows Server Rights Management Services CAL. Required for granting rights to files. Available per user and per device. This right is also included with Azure AD Premium licenses. An External Connector license is available for external users.
- Microsoft Identity Manager CAL. Required to use Microsoft Identity Manager 2016 functionality. No Microsoft Identity Manager 2016 CAL is required for users who only use the Microsoft Identity Manager sync service. Only available per user. This right is also included with Azure AD Premium licenses. An External Connector license is available for external users.