CAL is a commercial software license that allow clients to use server software services. Most commercial desktop apps are licensed so that payment is required for each installation.

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Licensing software with CALs and MLs can be complicated due to the technical nature of server products and networks. Microsoft offers a device-based CAL (Device CAL) or a user-based CAL (User CAL) for purchase. In addition, an External Connector (EC) license is offered for some products as an optional alternative to address specific customer scenarios.


For managing devices, Microsoft offers Server MLs for managing server operating system environments (OSEs). For managing non-server devices, Microsoft offers OSE Client MLs and User Client MLs.


This overview is for reference purposes only. Before purchasing, you should visit the "How to Buy" section for each product and consult your Microsoft representative or local reseller regarding your specific licensing needs.

User CALs


Client Access License based on user

Device CALs



External Connectors


  • Acquire CALs for each of your external users.


External Connector licensing


Server Licensing not requiring CALs

Some server products are available to be licensed on a "per core" or "per instance" basis.

Per Core licensing

Under the Per Core model, when the server software is running in the physical OSE, you must license all physical cores on the server. To determine the number of core licenses you need, count the total number of physical cores for each processor on the server, and then multiply that number by the appropriate core factor. You do not need to purchase additional CALs.


Specialty Server licensing

Specialty Servers are server-only licenses that generally do not require CALs. Specialty Servers require a server license for each instance of the server software running on a server. You can run the instance in a physical or virtual operating system environment. By exception, some products provide more specific use rights.

Management Server licensing

Under the Management Servers licensing model, you must acquire and assign the required number of appropriate category (server and/or client) and type (OSE and/or User) of ML to the device on which OSEs are to be managed. Included with the ML are the rights to run the corresponding management server software, so you do not need to acquire separate licenses for the management server software.


Management of server OSEs requires Server MLs (only OSE type offered), while management of non-server OSEs require Client MLs (OSE/User types offered).

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