CAL stands for "Client Access License." It is a license that grants users or devices the right to access the services or features of a server. CALs are particularly relevant in the context of Microsoft server products such as Windows Server, SQL Server, Exchange Server, and many others.
There are two main types of CALs:
User CALs: This type of license grants a specific user the right to access the server from any device (such as a workstation, home PC, smartphone, etc.).
Device CALs: This type of license grants a specific device the right to be used by any user to access the server. This option can be more cost-effective when multiple users use the same workstation or device to access the server.
The choice between User CALs and Device CALs depends on the specific usage scenario in a company or organization. Microsoft offers these flexible licensing options to accommodate different business models and work practices.
CALs are necessary because Microsoft's server operating systems and some other server products are licensed based on the principle of access licenses. This means that, in addition to the license for the server itself, additional licenses are required to legalize access to that server.