Windows Server
Microsoft's server operating system. Licensed per physical core (16-core minimum per server) with separate Client Access Licenses (CALs) for each user or device that connects.
Also known as: Windows Server Standard, Windows Server Datacenter
At a glance
- Licensing model
- Per-core (16-core minimum) + per-user or per-device CAL
- Related entities
- CAL · RDS CAL · Software Assurance · Datacenter edition · Standard edition · Hyper-V
Frequently asked questions
CSP vs Volume Licensing — what is the difference?
Cloud Solution Provider (CSP) is the modern Microsoft channel where a partner manages your subscription. Billing is monthly or annual, seats can scale up and down each month, and the partner handles support tickets. Best for cloud-first workloads (Microsoft 365, Dynamics 365, Azure) where flexibility matters.
Volume Licensing (Open Value, MPSA, Enterprise Agreement) is the traditional channel for perpetual on-premises licenses — Windows Server, SQL Server, Office LTSC. Three-year commitments are typical, with optional Software Assurance for upgrade rights. Best for perpetual server licensing where you want to own the asset.
Most organizations use both: CSP for the cloud subscriptions and Volume Licensing for the on-prem perpetual licenses.
What is Exchange Server SE and how is it licensed?
Exchange Server Subscription Edition (SE) is the successor to Exchange Server 2019, released in 2025. Functionally it is an in-place upgrade from Exchange 2019 CU14 with no schema change — the same servers, the same admin model.
The licensing model is the change. SE moves Exchange from perpetual + CAL to a subscription: you pay annually per server and per CAL, with continuous updates as long as the subscription is active. There is no "perpetual" SE — Microsoft is consolidating on subscriptions for on-prem server products, starting with Exchange.
Do I need both a Windows CAL and an RDS CAL?
Yes. Every Remote Desktop Services user or device needs both: a Windows Server CAL (for the underlying OS authentication) and an RDS CAL (for the Remote Desktop session). This is one of the most common compliance misses in audits — teams remember the RDS CAL and forget the base Windows CAL.
The two CALs are independent — you can buy User CALs on the Windows side and Device CALs on the RDS side, or any other combination, as long as the count works out for that user or device.
Do I need to license external users for SharePoint Server?
No separate per-user license is needed for external users — Microsoft Product Terms include external user rights with the SharePoint Server license. An external user is defined as someone who is not an employee, contractor or vendor of your organization or an affiliated entity.
The catch: those rights apply to your SharePoint Server, hosting your content for your business. You cannot stand up a SharePoint Server to host content for a third party — that is a Service Provider scenario and requires the Service Provider License Agreement (SPLA).
When is Software Assurance worth paying for?
Software Assurance (SA) adds roughly 25–29% per year on top of a perpetual Volume License. It is worth it when you actually use the benefits:
- Version upgrades — the biggest benefit. Without SA, every major upgrade is a fresh purchase.
- License Mobility — needed to run server workloads (SQL Server, SharePoint) on Azure or AWS using your existing license.
- Azure Hybrid Benefit for Windows Server and SQL — saves roughly 40% on Azure VM and SQL DB pricing.
- Training vouchers, planning services, 24/7 problem-resolution support.
SA is rarely worth it for desktop apps you do not plan to upgrade. It almost always pays for itself on Windows Server, SQL Server and Exchange Server in 3 years.
User CAL vs Device CAL — which one is cheaper?
The math is simple. Count how many users and how many devices will access the server. Whichever number is smaller is the SKU you want.
If 30 staff each have a laptop, a phone and a desktop (90 devices, 30 users), User CALs win — you buy 30 instead of 90. If 20 shift workers share 5 shop-floor terminals around the clock (5 devices, 20 users), Device CALs win — you buy 5 instead of 20. The CAL type is set per server role, so the Exchange Server and the Windows Server in the same rack can use different CAL types.
What is the Microsoft Admin Center for Volume Licensing?
Microsoft retired the old VLSC (Volume Licensing Service Center) in 2024 and consolidated all licensing management into the Microsoft 365 Admin Center and the Microsoft Cloud Partner Program portal. Volume Licensing customers now download keys, view orders and manage agreements under "Billing → Your products" in the Microsoft 365 Admin Center, signed in with the tenant's global admin or billing admin role.
If you still see references to VLSC in older documentation, mentally swap it for the M365 Admin Center.
What is a CAL?
A Client Access License (CAL) authorizes a user or device to access a Microsoft server product such as Windows Server, Exchange or SharePoint. The server itself needs its own server license; the CALs cover who connects to it. Without enough CALs, you are technically out of compliance even if every server license is paid for.
CALs come in two flavors. A User CAL follows a person across every device they use, which is the right choice for staff with a laptop, a phone, and a desktop. A Device CAL is tied to a specific machine and covers anyone who logs into it — better for shift workers who share kiosks or shop-floor PCs.
How does Windows Server core licensing work?
Windows Server 2019, 2022 and SE are licensed per physical core, sold in 2-core packs. The minimum is 16 cores per server — even if your hardware has fewer, you license to that floor.
Two more rules. Every processor must be licensed for at least 8 cores. The whole server is licensed even if Windows Server runs in only one VM — you do not get to license a slice. In virtualized environments, Standard gives you 2 VM rights per fully licensed server (stackable), Datacenter gives you unlimited VM rights.