Client Access Licenses: What Are CALs and Do I Need Them?

Windows Servers require CALS (Client Access Licenses)--here's who needs to use them.

Fully utilizing the services of a Windows Server environment requires the proper licenses. Most people are aware of the need to license the server software itself. However, one aspect of the licensing process that catches many by surprise is CALs (Client Access Licenses).

If you are running a Windows Server environment, then you need to know about Client Access Licenses. This guide discusses what CALs are, who needs them, and what types of CALs are available.

In simple terms, a CAL is a requirement for each user or device that accesses the services of a server. However, the picture is more complex than just this statement; but it does allow us to draw a simple comparison between server licenses and CALs.

Server licenses are like operating system licenses on any standard PC or laptop. The license grants the right to run the server software on a single server.

Now, with a standard Windows PC, this license covers everything, including using your computer's services remotely. There are plenty of ways to remotely access your computer and use your software, printers, email, and any other feature you wish. Although you may choose to purchase software to do this, there are no further licensing costs to consider.

The picture is different with a Windows Server License. The fundamental difference is that any device or user wishing to access a server's services will require a separate license—a Client Access License.

Not all Windows Server services require a CAL. If all your server is solely being used for is data and printing services, then there is no need to acquire CALs. However, for server services including the ones listed below, CALs are normally required.

This is the point in the story where things start to become a little more complicated! Because not only do each of these services require its own CAL. But also, as we will discuss next, not all versions of Windows Server will require CALs.

To muddy the water further: not all versions of Windows Server will require you to purchase CALs.

The most notable example of this is the Windows Server Essential edition. This version allows up to 25 users and 50 devices to access server services without CALs. There are also limitations on the number of cores, sockets, and virtual machines that the server can run.

Factors like processor cores have a direct bearing on the performance of the server. Processor cores are like the engines that power the server. They are one of the main determining factors to consider when you are planning the deployment of your server.

This means that small businesses and startups that do not need powerful servers which provide services to many users can avoid the need for CALs.

The final factor to consider is also one of the most important: whether to opt for Device or User CALs. As the names suggest, Microsoft issue CALs on a User or Device basis. A user CAL allows a single user access to the server. Importantly, this can be from any capable device.

A Device CAL is allocated to a single device. Any user that uses the licensed device has access to the server's services.

This distinction needs to be considered carefully when you are choosing the right licensing model for your server deployment. The diagram below is a simplified visual of the factors to consider.

Of course, the reality is rarely as simple as this. But considering these factors allows you to set a baseline that is the foundation of your CAL licensing strategy. The Microsoft Client Access Licence page has plenty more information about choosing the correct CAL.

The above is a very simplified description of a complex topic. What it does provide is a clear picture of all the factors that need to be considered when ensuring your server environment is properly licensed. It also ensures that your server can offer the full range of services that are critical components of the way we work today.

Bob is a professional writer who has been writing extensively on technology topics since 2020, with a focus on AI, software, hardware, SaaS, and networks. Prior to becoming a writer, he owned and operated an IT firm in Scotland for over twenty years.He currently resides in Spain and continues to provide valuable insights and analysis on the latest developments in the tech industry.