I ask because in the architecture diagram on wikipedia, it indicates the "host" OS (root partition) is on a par with the "guest" (child partition), with Hyper-V components below all of them.


If that is the case then the host OS is itself being virtualized, so will suffer from that overhead even if there are no guests installed.


  • Do the hypervisor/vm-bus only get installed once you select the Hyper-V role, or are they below the surface on every Windows Server R2?
  • Does adding the Hyper-V role require a reboot?
  • How does the presence of the Hyper-V components affect performance of the root partition?
  • Is the performance of root identical to child partitions?

Note: I am using Windows Server 2008 R2.

Thanks, Jack

4 Answers 4


Ok, just to add to this with some REAL WORLD information.

I ran (I say ran as have not tested under SP2 or the new R2) 2k8 and HyperV on my laptop fully patched to the latest Required & Recommended updates.

Disabling HyperV via boot and also registry I was able to confirm that running HyperV does affect your machine performance:

Vegas 2 (3d First Person Shooter):

  • With HyperV enabled (no guests running) Jerky Video rendering game as just playable
  • No Hyperv enabled (and no guests) no problems at all.

Of course this is hardware dependent but goes show the HyperV does tax some system resources.

YMMV with your performance testing.


  • TOSHIBA Satellite P300 PSPC4A
  • 2.50 gigahertz Intel Core2 Duo
  • 4Gb RAM
  • 2x 320.07 Gb HDD (Independant Drives ie: No RAID or Dynamic Discs)
  • ATI Mobility Radeon HD 3650

Assuming you're talking about Microsoft's Hyper-V technology, part of the Server 2008 stack.

You're correct - all operating systems are "guests" within Hyper-V, even the so-called host-OS, though the host does have special privileges.

The overhead is supposed to be pretty low though, so it's likely not something to worry about.

Source: A RunAs radio podcast (sorry, don't remember which one) talking about using PerfMon for performance monitoring. One side-effect of this arrangement is that performance counters for things like Disk-IO rates only measure the HostOS, and don't include activity of hosted virtual machines. If you want whole-machine metrics, you need to use specific Hyper-V performance counters.


AFAIK the term HyperVisor applies to the operating system hosting the virtual machines (be it bare-metal like VMWare ESX or hosted, like VMWare Server).

With that in mind, the Windows Server box will become the hypervisor, but will not be virtualised. At least by my understanding anyway.

If someone knows better, let us know!


It is true that the Host OS itself doesn't get virtualized, I can say that for at fact. I use the Server 2008 as a workstation with Hyper-V running a XP workstation.

When I turn the virtual XP off, I don't feel have any performance issues at all, actually not even when it is running.

You do need to reebot after installation though.

  • interesting a lot of these answers seem to be contradictory...
    – Schneider
    Aug 18, 2009 at 11:59

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