Before encountering this Emulation, paravirtualization, and pass-through: what you need to know for client hypervisors article, I only knew of the generic term "Hypervisor".

What added to my confusion was the article's statement

"...both VMware and Citrix are working on client hypervisor implementations of their own, and that they both have eluded to releasing products before the end of the year."

"end of the year" means 2009 but VMWare Workstation was there way before then (2005 or earlier). Isn't VMWare workstation a client hypervisor? If so, why would the article claim that VMWare is still working on a client hypervisor in 2009?

Please help me clarify the confusion between the two terms.

Is there a difference at all between the two terms? If so, what is it?


The basic definition of a client hypervisor is a hypervisor that is designed for use on a client machine (desktop, laptop, etc.), rather than a server. Some popular examples would be VMware Workstation, VirtualBox and VirtualPC (Microsoft). They're not intended to be used for production systems, and don't have the same feature sets as full hypervisors that are intended for production use.

It looks like that article you linked is talking about type-1 hypervisors, which is why VMware Workstation and other type-2 client hypervisors aren't considered.

  • As above. Citrix now do XenClient which is a Type 1 hypervisor designed for client deployment - I.e., it runs on a user's PC and whatever they interact with is virtualised. I don't think the whole concept really took off and Citrix don't seem to be spending any real time pushing it. – Dan Mar 1 '15 at 18:54
  • Thank you for highlighting type-1 vs. type-2. Now that you mentioned it, this makes a lot of sense. I was aware of the the basic definition of "client hypervisor" and VMWare Workstation meets this definition (as I alluded to in my OP), that is why I was so confused. But your explanation about an implied focus on type-1 only clarifies the issue. – Bill The Ape Mar 1 '15 at 19:22

The correct term is VDI hypervisor. It refers to a hypervisor that runs on server hardware, but runs desktop (client) operating systems, rather than server operating systems, as guests. The concept, which the article mentions, is desktop virtualization. When VDI hypervisors are combined with clients (either thin clients or (low end) physical PCs running some kind of remote desktop software) and (sufficiently fast) networking, you have a VDI (Virtual Desktop Infrastructure).

The 3 most common VDI hypervisors are:

  1. VMware View (ESXi/vSphere + related software)
  2. Citrix XenDesktop (XenServer + related software)
  3. Microsoft VDI (Hyper-V + related software)

Some common features of VDI hypervisors are:

  1. A remote desktop protocol with support for audio, video playback and/or 3D graphics.
  2. GPU Virtualization.
  3. Forwarding of devices, such as arbitrary USB devices, from a client (physical PC or thin client) to the VM.
  4. Assigning 1 VM to each user.
  5. Memory deduplication and shared hard disk images (not unique to VDI hypervisors, but especially important for them.)

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