Microsoft Per Core (with CAL) licensing rules

  • Release version: Yokohama
  • Updated January 30, 2025
  • 3 minutes to read
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    Summary of Microsoft Per Core (with CAL) licensing rules

    The Microsoft Per Core (with CAL) licensing model applies to various Microsoft Server products such as Windows Server, System Center, and Core Infrastructure Server Suite. This model requires licenses based on the number of installations and operating system environments (OSE). Licensing rules differ for on-premise and cloud installations, with cloud following Bring Your Own License (BYOL) principles.

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    For on-premise deployments, licensing can be managed either by physical cores on hosts or by individual virtual machines (VMs), but not at the cluster level. ServiceNow’s Software Asset Management (SAM) application supports both methods and can automate license allocation to optimize costs.

    Licensing by Physical Cores

    This method follows Microsoft's rules introduced in 2016 and involves licensing the physical cores on the host servers.

    • License count: Number of licenses equals the total physical cores (CPU count multiplied by core count).
    • Minimum licenses: 8 licenses per physical processor, 16 licenses per server minimum.
    • CAL requirement: Device or user Client Access Licenses (CALs) are required for users or devices accessing the server.
    • Virtualization rights: Licensing all cores grants rights to run 2 virtual machines; additional VMs require re-licensing (license stacking). Windows Server Datacenter edition allows unlimited VMs when all cores are licensed.
    • License mobility: Licenses can be reassigned to servers within the same environment every 90 days, but Windows Server does not support license mobility within server farms.
    • Cluster virtualization impact: For virtualized clusters (e.g., VMware vSphere, Microsoft Hyper-V), servers that VMs can migrate to must be fully licensed as if the VM is running on them, per Microsoft’s rules.

    Licensing by Individual Virtual Machines

    Introduced in 2022, this option licenses VMs based on their virtual cores and requires Software Assurance or subscription licenses.

    • License count: Number of licenses equals the total virtual cores on the VM (CPU count × core count × CPU thread count).
    • Minimum licenses: 8 licenses per virtual machine.
    • License mobility: Supported within the same server farm with no 90-day reassignment limit. The 90-day rule applies only when moving licenses across server farms or to cloud providers.

    Practical Implications for ServiceNow Customers

    • Understand your deployment environment (physical hosts vs. virtual machines) to choose the appropriate licensing model.
    • Use the SAM application to automate license allocation and optimize costs based on your actual infrastructure and virtualization technologies.
    • Comply strictly with Microsoft’s minimum license requirements and virtualization rights to avoid compliance issues.
    • Consider the impact of cluster virtualization and VM mobility on your licensing needs, as licenses may be required on multiple hosts due to VM migration capabilities.
    • Ensure Software Assurance or subscription licenses are in place if opting for licensing by virtual machines.

    The Per Core (with CAL) metric licensing model is followed by various Microsoft Server products such as Windows Server, System Center, and Core Infrastructure Server Suite. The number of licenses depends on the number of installations and operating system environments (OSE).

    The licensing rules for on-premise installations of these products and the cloud installations are separate. The cloud licensing rules follow Bring Your Own License (BYOL). For more information, see Licensing rules for BYOL and BYOS.

    To license the on-premise installation of these products using the Per Core (with CAL) licensing model, consider the following two options.
    • Licensing by physical cores, also known as licensing by physical hosts
    • Licensing by individual virtual machines
    Note:
    You can either allocate to individual hosts or individual virtual machines, not to cluster.
    You can either allocate manually, or the Software Asset Management application can automatically select the most cost-effective licensing option based on optimization criteria. For more information about how to perform allocation, see Allocation management and how the Software Asset Management application performs automated optimization, see View realized and potential cost-based licensing optimizations for Microsoft.
    Note:
    Both options, whether licensing by physical cores or licensing by individual virtual machines, come with their own set of Microsoft rules that must be followed. For more information, see Windows Server Standard, Datacenter, and Essentials.

    Licensing by physical cores

    The Software Asset Management application supports licensing by physical core rules, introduced by Microsoft in 2016.
    Table 1. Licensing by physical core rules
    Rule Windows Server Standard Windows Server Data Center
    Required number of licenses Equals the number of physical cores on the licensed server

    The physical cores on servers are equal to CPU count * Core count.
    Min licenses required
    • 8 per physical processor
    • 16 licenses per server
    CAL requirement Device or user CALs are required for users or devices accessing the server
    Virtualization rights Rights to use 2 virtual machines if all cores of the host are licensed with the option for license stacking
    Note:
    You must license the host again to get rights to use 2 additional virtual machines.
    		 Rights to run unlimited virtual machines when all cores of the host are licensed
    License mobility within Server Farms (Software assurance benefit)
    Note:
    License mobility isn't available for Windows Server. Licenses can be reassigned to servers as often as every 90 days.
    		 Not supported
    When deploying Microsoft products like Windows Server or System Center (using the core with CAL license model) on cluster virtualization technologies such as VMware vSphere, Microsoft Hyper-V, or Nutanix AHV, the number of licenses required for the physical host depends on the virtual machines that could potentially migrate to it within the cluster.

    Technologies like VMware vMotion, which enables live migration of virtual machines across all hosts, and host affinity, which helps lock virtual machines to hosts within a cluster, manage the movement of virtual machines across hosts. To understand more about cluster virtualization technology and its support on the Software Asset Management application, see Understanding your cluster infrastructure.

    According to Microsoft licensing rules, if a virtual machine with a Microsoft product like Windows Server installed is hosted on one server but can potentially migrate to another, the destination server must be licensed as if the virtual machine is already running on it.

    Licensing by virtual machines

    The Software Asset Management application supports licensing by individual virtual machines rules, introduced by Microsoft in 2022.

    Table 2. Licensing by individual virtual machines rules
    Rule Windows Server Standard and Windows Server Data Center
    Required number of licenses Equals the number of virtual cores on the virtual machine

    The virtual cores on servers are equal to CPU count * Core count * CPU thread count.
    Min licenses required 8 licenses per virtual machine
    Software assurance or subscription license
    Note:
    The option to license by virtual machine is only available with software assurance or a subscription license.
    		 Required
    License mobility within Server farms (Software assurance benefit)
    Note:
    Licenses can be reassigned within the same server farm as often as needed. The 90-day rule applies only when moving to another server farm or cloud provider.
    		 Supported