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Demystifying Microsoft virtual desktop licensing: SA vs. VDA vs. CDL

Virtual desktops are so dynamic that licensing them isn't easy. Microsoft's complex VDI licensing rules certainly don't help.

When it comes to virtual desktop infrastructure, administrators have a lot of choices. You may have wondered about the differences between VDI software options, remote display protocols or all the licenses out there. In this series, we tackle some of the biggest head-scratchers facing VDI admins to help you get things straight.

Figuring out Microsoft's rules for licensing virtual desktops is no easy task. The confusion around Microsoft VDI licensing stems from two reasons. First, there are many ways to implement virtual desktop infrastructure (VDI), making licensing different for each organization. Second, the vendor has so many different products -- and licenses for those technologies -- that it can barely keep track of itself.

That means you, the VDI admin, need to keep track of virtual desktop licensing requirements. For Windows desktops, you should understand Software Assurance, Virtual Desktop Access and -- as BYOD initiatives grow -- the Companion Device License. Let's get this straight:

Software Assurance vs. VDA

What is Software Assurance?
Software Assurance (SA) licensing provides Windows desktop customers with technical support, training vouchers, home-use rights and other benefits. But you have to pre-pay a percentage of the license price to account for future software upgrades. SA makes the most sense for organizations buying in bulk. Otherwise, it may be too expensive.

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Who needs the Virtual Desktop Access license?

Microsoft overhauled its virtual desktop licensing in 2010 because customers weren't happy with the per-device model. To run Windows virtual desktops, you needed the Virtual Enterprise Centralized Desktop (VECD) license, and having Software Assurance on top of that made virtualization a bit cheaper.

Still, the expensive VDI licensing program led Microsoft to add roaming rights and release the Virtual Desktop Access (VDA) license, which is $100 per year, per device. If you have Software Assurance, VDA rights are included, so you don't need any extra licenses to run VDI. However, non-SA customers and customers that run thin clients need the VDA.

Fitting licensing into your Windows VDI environment

Microsoft VDI licensing cuts costs only for SA customers
If your organization runs thin clients and can't afford Software Assurance, Microsoft VDI licensing hits hard. Microsoft has said that customers using thin clients aren't included under the virtual desktop access rights in SA because thin clients don't require a client OS. Still, you may save money in the long run by implementing virtual desktops rather than physical desktops because of energy and hardware cost reductions.

How client hypervisors factor in -- or don't
Microsoft isn't clear on its client hypervisor licensing rules. Software Assurance customers can use client hypervisors to run up to four Windows environments on a corporate desktop that's licensed with SA. For non-SA customers, the company doesn't provide specific regulations. However, Microsoft will release its own Hyper-V Client hypervisor with Windows 8, so its licensing policy should become clearer.

Virtual desktop licensing costs could hinder adoption
It took a while for Microsoft to come around to desktop virtualization, because with customers using VDI, that could cut into its profits from desktop management and hardware. For many businesses, the vendor's licensing policies still prevent VDI adoption. That's especially the case if you don't have SA, because you must purchase SA with the original desktop license and can't add it to older computers.

More on Microsoft virtual desktop licensing

Microsoft virtual desktop licensing guide

Microsoft FAQ on VDI licensing

Four ways Microsoft is screwing desktop virtualization

VDI project pitfalls: Licensing and more

Cost-effective ways to license non-Windows clients

If you use thin clients, look into cheaper ways to license your Windows virtual desktops -- with or without the VDA. Third parties offer thin clients that come with SA or sell clients that you have to buy VDA for. Manufacturers could even offer Certificate of Authority licenses to help thin client customers get around the VDA.

Another alternative is to run Windows Server VMs instead of desktop VMs. That would require you to buy Remote Desktop Services client access licenses, however, so it may not be much cheaper than just buying the VDA.

How to license virtual desktops in the BYOD era

Windows 8 VDI licensing includes BYOD
Microsoft updated its Windows 8 VDI licensing to include rules for bring your own device (BYOD). It added the Companion Device License (CDL), which organizations need to purchase for each non-Windows device that accesses a corporate virtual desktop. The CDL allows employees to access VDI-based desktops from up to four other personally owned devices under one license.

How the CDL will or won't help you
If you don't already have VDA licenses for mobile devices that access virtual desktops in your office, you'll have to buy the Companion Device License for every tablet or smartphone. For many organizations, this adds more licenses to keep track of and more cost. Plus, it doesn't matter whether the company or the user owns the device. Everything must be licensed.

Does Windows RT get a free ride from VDI licensing?
Windows RT devices, which run ARM-based processors, include VDA rights. That might be a better alternative than VDA for companies that supply phones or tablets to their employees. Employer-bought devices aren't covered under the CDL, so they'll need full VDA licensing, Office licensing and possibly other client access licenses. Still, Microsoft's language around using Windows RT devices to access VDI isn't clear whether it's the same access as the CDL provides.

Dig Deeper on Terminal Services and Remote Desktop Services

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What's the most confusing part of Microsoft VDI licensing?
Not clear why I need a VDA license to run a Windows desktop OS if I have already licensed the desktop OS. The desktop OS is running in a VDI environment so that is licensed, all I am doing using XenDesktop is presenting the desktop OS remotely on a laptop - so I only have 1 desktop OS running - why do i need the expensive VDA? It is very confusing...
Does anyone keep a current list of software applications that are VDI ready? I understand that there are a lot of software packages that are not compatible for use in a VDI environment, no licensing available for using like that.
Microsoft doesn't understand the device independence revolution.
The licensing model is absurd. It would make a lot more sense to just allow at least some of the windows licenses to be able to run inside a VM, and allow to access it by any means as well as only the registered user has access, or even any user if it's only 1 at a time.
So, if you want to build a VDI, it would suffice to buy one windows license per VD + a thin client, linux PC, whatever for RDP into it. Or if using windows as a client, another license for the client. Then if they want to make offers like SA clients getting the benefit of one or more licenses to install the VD, so be it, but don't make it the only option.
"What’s the most confusing part of Microsoft VDI licensing?"

... you mean beyond everything?
I buy a license for the OS I want to run, and I install it on a VM host. 
Now, if I run it from the host console, I'm fine... but I can't let an end user have console access.
If the end user has a PC with another licensed copy of Windows on it, they need to pay yet another fee for the right to access the already paid for version on the VM host. Unless they're already paying additional fees for another MS add-on product/service, or a slightly different but equally convoluted add-on plan. But if they haven't paid up for a Windows client to access the hosted Windows OS, there's a different fee due...

The more I look into MS virtual licensing, no matter if its Server, SQL, Desktop, Office, etc, the more it feels like putting on a shirt made of hornets.
VDA Licensing for a Zero Client Device and no Microsoft SA is not mentioned.
I can't figure out the difference between VDI, terminal services, and Citrix. As all microsoft licensing is getting more expensive and hardware cheaper (BYOD) how about what is VDI any why is it better than RDP?
it is really crazy to pay for nothing
the whole "multiple licensing" is a pain in order to implement if you want to stay legal. MS presents itself as not wanting anyone to do vdi unless they sell as many units as they always have
Everything and trying to understand all the scenarios. This doc helps but even your reps get confused on the subject.

Citrix Engineer Mid-Atlantic
Microsoft is just trying to stop or hinder the trend to desktop virtualization. As a final result most of the customers will choose another platform for desktop virtualization.
THis should be simple...
Vda is for non-windows devices - does that exclude an old pc running windows 7 thin pc which has SA?
In tune is overly expensive as a solution to this issue
What about thin clients running win7 like the wyse c90lew?
MS is a show stopper!
always changing, and there remains always some mysteries...
How to actually implement it i.e. what license key to install into a base image for VDI that will be rolled out?
There is no understanding for me, because I dont know what is the part from Microsoft they deliver extra to get extra money.
Microsoft won't settle on a licensing model than anybody can follow from one year to the next, making it nearly impossible to comply without a degree in Microsoft licensing. So much for their "trust initiative."
Are ya kidding me, You should fire the whole MS licensing group. MS licensing is a joke, your own internal teams cannot keep it straight.
The article seems to assume a lot of. prior knowledge. I really still don't understand the basics of what you are talking about.
The whole aspect of Microsoft licensing as it pertains to BYOD devices and the "any device from anywhere" montra. The licensing is confusing and overly expensive to the point that comapnies may look to restrict or move from Microsoft to an alternate or cloud based offering that is more easily managed with a fixed cost model.
There needs to be a class action lawsuit against Microsoft for predatory and obtuse licensing policies...if anyone could every understand what they are.
I bought 3 Windows 8 Pro retail copies hoping to put them into a zen box and resell, but it sounds like this is not covered under the licensing. It should be. I've only run across this page looking for technical information, not licensing information. I didn't think virtual machines were licensed differently. Should of thought of it. I will be returning these licenses. Thanks for your assistance.
If I am using zero clients then do I just need Windows 7 lic. for each virtual desktop or do I require more licensing? I am VERY confused!
Everything is still clear as mud. What about cloud based systems? Multi-tenant systems, What about systems not used by employees?
When do you need a VDI Suite license?
MS desktop licensing without virtualisation is confusing and difficult enough. With a virtualisation layer it is almost impossible (possibly IS impossible). The danger for Microsoft is if they try and enforce their rules, people WILL look for alternatives, and alternatives will be there, so I suspect as long as you are seen to be reasonable they will not have an issue. But MS should have a good hard look at the storm that is coming... the virtual and cloud world will change the rules around them, and it will just take one good alternative and MS will lose half of the revenue they are trying to create with their outdated and confusing licensing models.
RDS license
Who needs VDA?
It' all confusing. I don't know how it would stand in court in EU, because of consumer rights there. If only somebody have the nerve, money and time to sue so that we know where we're standing.
is this true: