SQL Server User CAL (Client Access license) is an authorization key for connectivity that allow the server to be accessed by a specific user irrespective of device. This will make a specific user users access server from using the specific login credentials. It is most appropriate for administrators who know the exact number of users and devices that will connect to the server. By implementation of User CAL, an admin can ensure better adherence to security compliances.
 
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Microsoft Corporation (commonly referred to as Microsoft or MS) is an American multinational technology company headquartered in Redmond, Washington, that develops, manufactures, licenses, supports and sells computer software, consumer electronics and personal computers and services. Its best known software products are the Microsoft Windows line of operating systems, Microsoft Office suite, and Internet Explorer and Edge web browsers. Its flagship hardware products are the Xbox video game consoles and the Microsoft Surface tablet lineup. As of 2011, it was the world's largest software maker by revenue and one of the world's most valuable companies.