CAL — Client Access License

A Client Access License (CAL) is a software license that grants a specific user or device the legal right to access and utilize the services of a Microsoft server software product. Unlike a standard software license that covers the installation of a program, a CAL is not a piece of software; it is a legal entitlement required in addition to the base Server license (under the "Server+CAL" licensing model) to ensure compliance with Microsoft’s usage terms.

Technical and Legal Distinction

In the Microsoft ecosystem, server software—such as Windows Server, SQL Server, Exchange Server, and SharePoint—is typically licensed in two parts. The Server License authorizes the organization to install and run the server operating system or application on a physical or virtual machine. However, this license alone does not permit users to connect to that server. Each connection requires a CAL to bridge the gap between the endpoint and the server infrastructure.

Core CAL Types

• User CAL: Assigned to a single unique individual. This person can access the server software from an unlimited number of devices (e.g., a work laptop, a home desktop, and a mobile phone). This is typically the most cost-effective option for organizations with employees who travel or use multiple devices.
• Device CAL: Assigned to a specific hardware device (e.g., a workstation or a handheld scanner). Any number of users can use that single device to access the server software. This is ideal for shift-work environments, such as nurse stations or call centers, where multiple employees share a single machine.

Where CALs Appear in Documentation

On a formal quote, Microsoft Customer Agreement (MCA), or Enterprise Agreement (EA), CALs appear as distinct line items. They are often listed by the specific product name (e.g., "Win Svr CAL 2022") or as part of a bundle, such as the Core CAL Suite or Enterprise CAL Suite, which packages multiple access licenses for Windows Server, SharePoint, and Exchange into a single SKU.

Common Misunderstandings

• Concurrent vs. Assigned: Microsoft does not offer "Concurrent" CALs. You cannot buy 50 CALs for 100 people and hope only 50 log in at once; every unique user or device must be licensed, regardless of how many are active simultaneously.
• External Users: Most servers require an External Connector license or specific CALs if non-employees (customers or partners) access the network, though some products include limited external access rights.
• Version Matching: CALs must be version-equivalent or newer than the server software. For example, a Windows Server 2019 CAL cannot be used to access Windows Server 2022, but a 2022 CAL can access a 2019 server (downward compatibility).

Practical Buying Advice

When purchasing, perform a "Headcount vs. Workstation" audit. If your staff count exceeds your device count (common in manufacturing), buy Device CALs. If your device count exceeds your staff count (common in modern offices), buy User CALs. Note that while Retail and Volume Licensing CALs are available, CALs are never sold as OEM products for separate purchase; OEM licenses are strictly pre-installed by hardware manufacturers and are permanently tied to the original hardware.

Closely Related Terms

• RDS CAL: Remote Desktop Services CALs are required in addition to standard Windows CALs if users access the server via a graphical remote interface.
• ML (Management License): Required for managing client devices via tools like Microsoft Endpoint Configuration Manager.
• Per-Core Licensing: An alternative model (standard for SQL Server) where no CALs are required if every physical or virtual core on the server is licensed.

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