Re: Understanding Windows Server Client Access Licenses (CALs)

***Disclaimer: this article is from 2018 and information are based on Windows Server 2016 edition. We suggest you to click on Help for Windows Server 2019 Client Access Licenses (CALs) for more update information about the same topic.***


Whether you are a customer or a reseller, it is important to understand the ins and outs of Windows Server Client Access Licenses (CALs) to ensure license compliance is met.

Today, we will explain CALs: what they are, the different types, and why they are important!

Windows Server 2016 Core-Based Licensing
First, let’s start with some basic Windows Server licensing information, we’ll call it 'Windows Server licensing 101'. Starting with Windows Server 2016 Standard edition and Datacenter edition, Microsoft introduced a new licensing model. This new model is based on the cores in the server, (where as previous Windows Server licensing models were based on processors). Although the licensing model has changed, one thing has stayed consistent… the need for CALs!
It is important to note that CALs are only required for Windows Server 2016 Standard and Datacenter editions. For Windows Server 2016 Essentials edition, CALs are not required.

Want to learn more about Core-Based Licensing? We’ve got the perfect video and blog for you! Check it out: Windows Server 2016 Core Based Licensing Explained


Microsoft Windows Server Operating System (OS) Licenses
When a customer purchases a Windows Server OS license (Windows Server 2016 Datacenter edition for example), they receive a license that allows them to install the operating system onto the server. However, the Windows Server OS license does not give them the legal right for users or devices to connect to the server… that is where CALs come in!

Microsoft Windows Server Client Access Licenses (CALs)
A Windows Server CAL is a license that allows customers to access Windows Server. CALs are used in conjunction with Microsoft Windows Server OS licenses to allow Users and/or Devices to access and utilize the services of that server OS.

If your customers are wanting to run Windows Server 2016 on their new HPE Gen10 server, they would acquire a Windows Server 2016 OS license in order to run the Windows Server software on the physical server AND they would need to acquire CALs for the Users or Devices who will access the server.

This two-component license models provides a low entry price and a way to pay for capacity used: the more devices or users accessing the server software, the greater the license fees or price. This model therefore offers license affordability to organizations of all sizes.


What are the different types of CALs?
HPE offers several different types of Windows Server CALs.

  • User CALs allow a single user access to Windows Server from an unlimited number of devices
  • Device CALs allow an unlimited number of users to access Windows Server from a single device

Does the organization have roaming employees who need to access the corporate network from several devices? In this case, User CALs make the most economical and administrative sense.

Does the organization have multiple users for one device, such as shift workers using a kiosk-style workstation? In this case, Device CALs make the most economical and administrative sense.

There is a third type of CAL that we must talk about, Remote Desktop Service (RDS) CALs. RDS CALS are required for users or devices that want to utilize Remote Desktop Service functionality on Windows Server. Regular User or Device CALs are required in addition to the RDS User or RDS Device CALs.
CAL types.jpg

More Fun Facts about CALs!
Windows Server CALs can be purchased from Hewlett Packard Enterprise, or an authorized partner, at any time and do not require a new HPE server purchase. HPE currently offers User CALs and Device CALs in packs of 1, 5, 10, and 50 CALs. RDS User and RDS Device CALs are available in packs of 5 CALs.

Windows Server CALs must be the same version as—or higher than—the server software they are accessing. In other words, users or devices accessing a server running Windows Server 2016 must have Windows Server 2016 CALs. Additionally, Windows Server 2016 CALs may be used to access Windows Server 2012 (but Windows Server 2012 CALs cannot be used to access Windows Server 2016).

It is imperative that businesses stay up to date with their CAL compliance requirements so they don’t fall behind or find themselves in error!

Adding new users? More User CALs may be required!

Adding new devices? More Device CALs may be required!

If you are a reseller, now is a great time to check in with your clients to ensure their CAL needs are filled! If you're a customer, now is a great time to check your server environments to ensure you're in compliance!

Have questions about HPE OEM Microsoft products/solutions, Windows Server 2016, or HPE Servers? Join the Coffee Coaching community to keep up with the latest HPE OEM Microsoft news and interact with HPE and Microsoft experts.

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About the Author


Willa manages the HPE | Microsoft Coffee Coaching program. Follow along to learn more about the latest HPE OEM Microsoft product releases and how the HPE Microsoft partnership can benefit partners and customers.


Hello Jorge,

A CAL gives users or devices the right to access and use services provided by a Windows Server. Windows Server CALs do not come with a “product key” (as Windows Server Operating System licenses do) and do not need to be registered anywhere in the OS. However, every user—or device—that access Windows Server needs a CAL to be compliant with Microsoft licensing regulations.


You can learn more about CALs in our Windows Server FAQ:

Hello Mohammad, 
CALs are ‘versioned’ in that they permit access to their CAL generation Windows Servers – or older generations of Windows Server within your domain.
Example: A Windows Server 2016 1 User CAL grants access to Windows Server 2016 / 2012 R2 / 2012 / 2008 R2 / 2008 – A Windows Server 2008 R2 User CAL for contrast grants a user access to WS2008 R2 or older Windows Server OS generations.


The critical question in the scenario you are asking about is: Do any of the users currently covered with Windows Server 2008 R2 level CALs require access to / are using Windows Server 2016 or Windows Server 2012 R2 services/roles? If the answer is yes, those users need to be covered by a Windows Server 2016 (or looking ahead Windows Server 2019) CAL.

CALs do not have a product key and are not registered in the OS so mixed-generation CAL environments are generally possible – always assuming all users that access a newer generation Windows Server OS are covered with an appropriate (same OS gen or newer) CAL.


Hi, I want to do CBT examination (computer based exam)  I am using Apache, MySQL and php deployed on my laptop running on windows server 2012  is it composery for me to have CAL on my server before students can have access to take exams?

Don Mason

This is a very helpful article, but I had one question on this topic. We've got 2 "application servers" our users are logging into published applications, let's say 25 users. I understand we'd need 25 User CALs, but for the RDS CALs, would we be able to buy just 2 RDS Device CALs and 25 User CALs? Or do the type of CALs need to match? Meaning, would we need 25 User CALs and 25 RDS User CALs? Thanks

Hi henryIkede, 

Yes, Windows Server CALs are needed. Keep in mind, CALs need to be at least Windows Server 2012 CALs or newer (CALs cover "downstream' OS generation -- ex: a Windows Server 2019 CAL covers access to an older generation of WIndows Server such as Windows Server 2012, but NOT 'upstream' generations -- ex: Windows Server 2012 CAs do not cover access to a Windows Server 2019 Server). Depending on the setup of the training infrastructure, either User CALs (if users are bringing their own client devices) or Device CALs (if the students are always using the same fixed/shared classroom workstations/kiosks) can be used. 

Hi Don Mason, 

To better facilitate your question, could you please email us at so we can gather some some specific information about your intrastructure?


The Coffee Coaching team

Sean McAndrew

I'm just wondering, does the enterprise administrator user for the domain also require a user/RDS CAL or is that the only "user" included with the Server 2016 license?

Hi Sean, 
As an exception to the CAL rules, up to two users or devices may access the server software, only for server administration purposes, without requiring either a RDS CAL or a Windows Server CAL.

Please let us know if you have further CAL questions 

The Coffee Coaching team

Licensing FAQ for Windows Server OEM products on HPE servers



Dear Willa,


With regards to Client Access License (CAL) as per your information provided above , No need of downgrade the Datacneter server license from 2019 to 2016 to match with clients current 2016 CAL version. 

Hello Lokesh_gs, 

If your client is currently running Windows Server 2019 Datacenter they will require Windows Server 2019 CALs. Windows Server CALs must be the same version as—or higher than—the server software they are accessing. This means that users or devices accessing a server running Windows Server 2019 must have Windows Server 2019 CALs (while users or devices accessing a server running Windows Server 2016 could use Windows Server 2019 CALs or Windows Server 2016 CALs.) Hope this helps clarify your situation!

The Coffee Coaching team

Licensing FAQ for Windows Server OEM products on HPE servers



I have WIndows Server 2016 Standard.  I was sold  WIN SVR CAL 2019 SNGL OLP NL VLIC USR CAL. Can I utilize the 2019 calls with 2016 server?

Hello sma5979177612, 

Yes. A Windows Server CAL permits access to all earlier versions of Windows Server. So you can use Windows Server 2019 CALs with Windows Server 2016. 

The Coffee Coaching Team


Hi there! I have a question for you. My company works in a Terminal server environment. The users connect remotely (via RDP) to the Windows server 2008 to login and make use of the programs/apps. I have 4 TS, which the users can choose the server they want to use every day.

My plan is to create 4 new virtual TS with Windows Server 2016 Standard. Besides purchasing Windows Server 2016 OS and Windows Server user CALs, I have it clear that for sure I will need RDS user CALs....Do I have to install all the RDS user CALs on each TS.....let me give you an example: Users: 50 TS: 4

TS01: 5 Users connected. TS02: 10 Users connected. TS03: 20 Users connected. TS04: 15 Users connected.

Do I have to install all the RDS user CALs on each TS? Do I have to distribute the CALs per TS? What if in TS01 are more users connected than usual or even though all the users move out to TS01 and TS02.

nice thing

Audy Syazwan

Hi, I want to utilize a Windows Server 2019 as a CoAP server and this server is installed with MySQL and hosted a few IIS web applications. If there are thousands of IoT devices going to transmit data to this server, do I need CAL for each device?

Hello Carlos,
you need a RDS CAL per each user or server which need access to remote.
As you mentioned about WS 2008 and WS 2016, I suggest you to take care about support option. In this new blog post you will find much more information: Understanding support options for Windows Server with HPE ProLiant servers

Hope I answer to your question, in case you need much more information please let us know.

Thanks a lot,


Hello Audy,

Thank you very much for your comment.

On a regular Royalty OEM Win Srv any *authenticated* access to the server requires a CAL, if this is a device connecting then it would require a Device CAL.
In case you of further questions please let us know.

Best regards,