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According to Wikipedia, there are Hyper-V and Hyper-V server. Ok...

Hyper-V server doesn't need an OS to run, so it is true Hypervisor. But what about Hyper-V inside windows2008, is it a "type 2" ?

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When Hyper-V runs as a role on Windows Server 2008 and Windows Server 2008 R2 it's still and hypervisor.

It is type 1 (bare metal) in both cases.

The trick here is that when you install Hyper-V as a role on Windows Server 2008 R2 you see the Windows Server like a host OS and it is not. The setup converts the original OS in something like a VM and puts the hypervisor below. This is what is called the root or parent partition of Hyper-V. That's why you experience the same sped in what you see as the "real machine" and the virtual machines.

You can find the Hyper-V Architecture at MSDN.

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I disagree with it being type 1. Because it heavily relies on the root partition and can't function without it. –  Alexey Frunze Nov 1 '11 at 23:34
@Alex: While a lot of OSes "talk" to the Root Partition, it isn't required. An "unenlightened partition" is perfectly capable of working without the help off the Root Partition. If anything it should be called "Type 1+2" but definitely not "Type 1". –  Bart De Vos Nov 1 '11 at 23:41
@Alex read the arquitecture. Is Type 1. It realies in the root partition for some things and it was designed this way basically to have a huge drivers compatibility and dont need specially hardware with special drivers. But the access to resources like proccesor, memory etc. dont pass throught the root partition. –  Ricardo Polo Nov 1 '11 at 23:48
@BartDeVos: Nope, incapable. See what VMWP does: [Virtual Machine Worker Process] also handles IRQs, memory and I/O port mapping through a Virtual Motherboard (VMB). Also note that Virtual Devices are managed by the Virtual Motherboard (VMB). Virtual Motherboards are contained within the Virtual Machine Worker Processes, of which there is one for each virtual machine. Virtual Devices fall into two categories, Core VDevs and Plug-in VDevs. Core VDevs can either be Emulated Devices or Synthetic Devices. Type 1.5. –  Alexey Frunze Nov 1 '11 at 23:54
@Alex, can you suggest a hypervisor which can function without the root partition, by way of comparison? –  Harry Johnston Nov 2 '11 at 3:23
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enter image description here

Whenever your virtualization-solution needs an OS (other then it's own for very basic tasks) to run on, it's "Type 2"-virtualization.

It looks like the Windows Server OS will virtualize itself when you install the server roll. The Hypervisor will be started initially on boot which will hand-over the boot process to Windows Server 2008, which is now the Parent Partition. The Parent Partition is also referred as the Root Partition. More info can be found in this article

So, Hyper-V is bare-metal and thus Type 1.

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Nice graphic. Makes it very easy to show the difference. –  mrdenny Nov 1 '11 at 22:54
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Hyper-V is a type 1 hypervisor, no matter whether installed as a windows server component or as "Hyper-V server".

In the former case, it looks as if it's a type 2 product because you install windows first, but when you install the hyper-V role, it essentially virtualises the windows server installation that's already present.

(see also datasheet from this page, and very large hyper-v virtualisation architecture "poster" here).

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The hypervisor is the same type 2 in both cases.

EDIT: OK, strictly speaking, based on the design, it's neither type 1 nor type 2, it's a blend of the two.

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-1. According to Wikipedia, that's not true. Even though Hyper-V looks like the hypervisor is running on a 2008 OS. It's actually a virtualized 2008 instance. –  kbyrd Nov 1 '11 at 23:12
Even though the Windows OS is minimal, the Hypervisor is not self-sufficient and does not run on bare hardware directly. It still needs Windows to function. The main reason being the Windows device drivers. Also, there's support for bitlocker. It would be a waste to duplicate bitlocker in the hypervisor and develop different drivers for it or rearchitecture it to work with them directly. The Hyper-V Server uses the same technology as Hyper-V on Windows Server, just doesn't give you the whole Windows OS. –  Alexey Frunze Nov 1 '11 at 23:28
No. It is Type 1. Not a blend. If you want to be techonrical the Hypervisor on Hyper-V is the only one thing that runs on the ring 1 of x86-64 arquitecture. Nothing more :). The other commponends that maybe are confusing you like the VMBus, the Virtual Machine Management Service etc most of them designed to let the virtual machines work faster with all hardware runs on a higher layer. If you read the arquitecture of other market leaders hypervisor you will find the same stuff and for that doesnt mean that are not type 1. –  Ricardo Polo Nov 2 '11 at 0:06
@RicardoPolo: emulated virtual devices (not only synthetic/VMBus) are emulated mostly in the root partition. The hypervisor emulates very few of them (e.g. CPU, local APIC). See the Hypervisor Functional Specification for what it does. Section 9.1.1 in particular explains how VM's accesses to emulated devices are intercepted by the parent/root partition and emulated there, not in the HV. VMBus & synthetic devices outside of HV do make things faster, but legacy/unmodified VMs don't take the advantage and still are emulated in root. –  Alexey Frunze Nov 2 '11 at 0:37
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