BLOG: Jeff Birnbaum

Microsoft VDA licensing: Another reason to choose NComputing vSpace over VDI


There are two technologies available to SMBs to deliver a centrally hosted Windows desktop experience to their users: Remote Desktop Services (RDS) or Virtual Desktop Infrastructure (VDI). RDS uses session virtualization to allow many users to log into the same instance of a Windows server OS and get a Windows desktop experience. VDI uses machine virtualization to allow multiple copies of a Windows desktop OS to run concurrently on the same physical server using a hardware abstraction layer called a hypervisor.

Both technologies allow the desktop applications to execute on a centralized server, allowing the end user PC to be replaced with a less expensive, lower wattage, more compact thin client device.

On the surface, VDI has advantages over RDS: VDI users can reboot or crash their Windows desktop VM and not affect other VDI users on the same server. VDI users can install their own software on their desktop and not affect other users. And VDI users can be offered guaranteed memory and CPU resources. But those advantages come at a high cost. Sharing of memory and disk I/O is much more efficiently handled by a single Windows OS as compared to a hypervisor managing many Windows OSes. The result is that 4 to 10 times as many users can share a single physical server using RDS as compared to VDI.

If that is not enough reason for SMBs to consider RDS over VDI, Microsoft gives you another reason: Virtual Desktop Access rights (VDA), a VDI licensing scheme introduced by Microsoft in 2010.

In order to access a Windows desktop OS running on a hypervisor (ie, a VDI virtual desktop) the device connecting to that desktop OS must either be covered by a Microsoft Software Assurance (SA) contract or must have a VDA subscription. The problem is only certain Windows desktop OS versions are eligible for SA and the SA contract must be purchased within 90 days of the OS purchase. This means that all lower priced Linux thin clients and zero clients are not eligible for SA and even many Windows Embedded thin clients will not be eligible for SA either. Therefore, you are likely to need to buy a VDA subscription for each of your thin client devices that are accessing a VDI virtual desktop. Current list pricing for a VDA subscription is $100 per device per year.

To see the cost implications of VDA, let’s look at an example of a virtualization deployment for 30 thin client devices. With RDS, Microsoft does charge a tax for accessing an RDS host: a server client access license (CAL) and an RDS CAL for each device or user. But these CALs are perpetual licenses – not annual subscriptions. The result of this licensing model difference over three years can be seen in the following table.  

Microsoft Licensing Cost for 30 devices over 3 years: RDS vs. VDI




Licenses needed

One server OS license per target server ($883)


For each client device: ( 1 Server device CAL ($30) and 1 RDS device CAL ($102)) x 30 = $132 x 30 = $3,960 30

30 target desktop OS licenses ($187 each) x 30 = $5,610


For each client device: VDA rights subscription ($100 / device / year) x 30 devices x 3 years = $9,000

Commercial License Cost



* Cost based on 30 thin clients (not eligible for SA) over 3 years, Windows Server 2012 R2 standard, Windows 8.1 Pro, US MOL pricing, corporate customers.


The end result over 3 years is 3 times the cost for VDI licensing vs. RDS licensing.

NComputing vSpace leverages Microsoft RDS to deliver virtual desktops to users at the lowest possible licensing and infrastructure costs. But unlike other vendors that use RDS, NComputing is the only company that provides both thin clients and a proprietary optimized remote access protocol. This combination results in better price / performance than other solutions, a single vendor for support, and integrated management of sessions and devices through a single interface. So when you are looking for a virtual desktop solution designed for organizations with limited budget, staff, and expertise, look at NComputing vSpace.

About the author

Jeff Birnbaum
Jeff joined NComputing in 2014 as a Product Marketing Manager for the vSpace product line. His career in IT spans over 30 years with roles in marketing, sales, business development, project management, product specification, and user interface development.