Presentation virtualization and desktop virtualization differ in their setup and functionality, yet they have similar licensing models. The trick is deciding which virtualization licensing model is best for your organization.
Presentation virtualization vs. desktop virtualization functionality
Both presentation virtualization and desktop virtualization models have benefits. Based on Microsoft's Terminal Services technology, presentation virtualization focuses on centralizing applications. Shareable applications are installed in a special mode on a server, where users can then access them via remote devices.
In Windows Server 2008, applications seamlessly appear on the desktop -- if the user relies on a full desktop device to access the working environment. If not, the end user works through a shared remote desktop, which simply a server operating system running in a special remote desktop mode. All users working with applications running on a presentation virtualization server share the same OS.
Unlike presentation virtualization, virtual desktops present individual OSes to end users. Users don't share applications, which are contained within the single desktop each user accesses. Activity within one user's virtual machine (VM) does not affect any other user in the organization or other users working with a desktop VM running on the same server.
The server running presentation virtualization relies on its own OS and applications installed within it, offering services to end users. The server running the virtual desktops does not need to associate with any of the applications installed within each VM. Alternatively, each VM operates on its own; the server's sole purpose is to make sure the VM is up and running.
Virtualization licensing models
Microsoft has licensing terms for both presentation virtualization and desktop virtualization. Desktop virtualization requires the Vista Enterprise Centralized Desktop (VECD) license and is acquired per device. If users run desktops or workstations to access centralized desktop VMs, then the devices being used must have a VECD for Software Assurance license.
A standard VECD license is needed in environments in which end users access desktop VMs using thin-client devices. If you have 100 devices and 300 users, you'll need to buy 100 VECD licenses. If you have 100 devices and 30 users, you'll still need to buy 100 VECD licenses. Be aware, however, that each VECD license allows a user to run up to four desktop VMs.
On the other hand, presentation virtualization licenses are based on Windows Server Terminal Services licenses. Terminal Services licenses can be based either on a per-device or per-user basis. To run Terminal Services, you must also have a license for each server running the Terminal Services role. In addition to the server license, you must obtain a Windows Server Client Access License (CAL) for each device or user accessing the server, depending on the license model you choose.
Finally, each user or device requires an incremental Terminal Server Client Access License. If you choose the per-device license structure, any number of users can access the shared presentation virtualization environment. If you choose to license per user, each user can access the Terminal Services environment from any number of devices.
The functionality between the two virtualization models is widely different, but the licensing models are similar if you choose to work on a per-device basis. The desktop virtualization model works best if you:
- Have more users than devices
- Have users that need to run multiple versions of the same desktop
- Run applications that must be isolated from each other and can be contained within different virtual desktops that users access through VECD.
You might want to consider presentation virtualization with a per-user CAL licensing model over desktop virtualization if:
- Users run highly compatible applications
- You have more devices than users
Carefully review your users' needs before you choose which model to trust. Refer to the following table when making your selection.
|Licensing model||Terminal Services||Desktop virtualization|
|Required licenses||Windows Server 2008 base license||Windows Hyper-V Server (free)|
|Server CAL||No CALs|
|Terminal Services CAL||VECD per device|
|License assignation||Per device||Per device only|
ABOUT THE AUTHORS:
Danielle Ruest and Nelson Ruest are IT professionals focusing on virtualization and continuous service delivery. They are authors of multiple books, including Virtualization, A Beginner's Guide which covers all aspects of virtualization in datacenters of any size, and Windows Server 2008: The Complete Reference which is focused on building virtual workloads with this new OS. They are currently writing a training guide for Microsoft Exam 70-652: Configuring Windows Server Virtualization with Hyper-V for MS-Press. Feel free to contact them at firstname.lastname@example.org for any comments or suggestions.