Client access licenses (CALs) aren't needed. It allows only one instance of the server software to be run in the physical or virtual environment (Essentials edition licenses can't be combined).

The Essentials edition is designed for small organisations with up to 25 users and 50 devices.

If you need to run additional virtual instances, you can acquire more Standard licenses. It allows you to run two instances of the server software in a virtual operating system on the licensed server.

The Standard edition is designed for small-to-medium-sized organisations.

Essentials shares many of the features of the Standard edition, but has limitations on the maximum number of users and devices that can connect to it. Microsoft offers Windows Server through Connecting Up in the Standard and Essentials editions. You can use this guide to find the Windows Server edition and licenses appropriate for your organisation's needs. As a server operating system, it is also the platform for separately acquired server applications such as Exchange Server or SQL Server. Windows Server is a server operating system that enables a computer to handle network roles such as print server, domain controller, web server, and file server.

Server essentials