Windows Server licensing causes more confusion than almost any other Microsoft product. It becomes simple once you treat it as two separate purchases.
Part one: license the server’s cores
- Every physical core in the server must be licensed.
- The minimum is 8 core licences per processor and 16 per server, even if the server has fewer cores.
- Licences are sold in packs. A 16 core pack covers the minimum for one server.
Example: a server with two 12-core processors has 24 cores, so it needs one 16 core pack plus eight additional core licences.
Standard or Datacenter?
| Standard | Datacenter | |
|---|---|---|
| Virtual machines when all cores are licensed | 2 | Unlimited |
| Storage Spaces Direct, software-defined networking | No | Yes |
| Typical use | Physical or lightly virtualised servers | Virtualisation hosts |
With Standard you can license all cores again to gain two more virtual machines. As a rule of thumb, once a host runs more than about ten to twelve virtual machines, Datacenter becomes the cheaper option.
Part two: client access licences
A core licence lets the server run. A client access licence (CAL) lets a person or device use it. You choose one type:
- User CAL: one per person, covering all their devices. Best when staff have several devices each.
- Device CAL: one per device, covering everyone who uses it. Best for shared workstations and shift work.
CALs are tied to a version. Windows Server 2025 CALs also cover access to earlier versions, but older CALs do not cover Windows Server 2025.
Remote Desktop Services
If users connect to desktops or applications published by Remote Desktop Services, each of them needs an RDS CAL in addition to the Windows Server CAL.
A worked example
A 25-person office with one 16-core server, where ten people work remotely through Remote Desktop, needs one Windows Server 2025 Standard 16 core pack, 25 user CALs and 10 RDS user CALs.
See the products: Windows Server licences and CALs. If you would like us to check your numbers, send us your server specification.