Client Access Licenses (CALs) are different from Windows Server software licenses. A Windows Server CAL is the license that gives users and devices the right to access a server installed with Microsoft Windows Server software.
Why should I buy CALs?
CALs are required by Microsoft licensing for all users or devices that access Windows Server Standard or Windows Server Datacenter. When a customer buys Windows Server Standard or Datacenter, they receive a server license that allows them to install the operating system on one computer. A server software license by itself doesn't provide the license rights to allow anyone to connect to that computer, whether they work for the company or not. Instead, each user or device needs a CAL.
What are my CAL buying options?
One user, unlimited devices
Ideal for companies with employees that use multiple devices.
One device, unlimited users
Ideal for companies with multiple users for one device, such as shift workers.
CALs are not included with any Windows Server 2012 or 2012 R2 editions.
No CALs required for Windows Server 2012 or 2012 R2 Essentials or Foundation.
CALs are required by Microsoft licensing for all users or devices that access Windows Server Standard or Windows Server Datacenter.
Windows Server 2012 CAL Customer Scenario
A small office with 15 users that access Windows Server 2012 R2 from multiple devices (desktops, laptops, tablets, phones) buys a server installed with Windows Server 2012 R2 Standard. They should also buy 15 Windows Server 2012 User CALs, one for each employee.
15 User CALs
1 Server License