Number of Supported Virtual CPU’s for a Guest on Hyper-V

How many virtual processors (virtual CPU’s) are officially supported by Microsoft for a guest virtual machine (VM) running on Hyper-V?

You may be thinking the answer to this question is four since that is the number you can assign to any guest VM, but the answer like many others in IT is that it depends. It depends on what guest operating system you’re running. Windows Server 2003, Windows Vista, and Windows XP SP3 all officially support a maximum of two virtualized processors when installed as a guest VM running on Hyper-V. This is according to the Microsoft Windows Server 2008 R2 website: “Virtualization with Hyper-V: Supported Guest Operating Systems” and Microsoft TechNet: “About Virtual Machines and Guest Operating Systems“. Both of these sites also list the maximum number of virtual CPU’s for all of the other supported guest operating systems such as Windows 2000 SP4 only supporting a maximum of one virtualized processor. This is something to keep in mind when virtualizing older operating systems as guest VM’s on Hyper-V.



  1. Mike Prest

    It’s interesting reading this as we have a Windows Server 2003 R2 VM and it shows 4 CPU’s in both Task Manager and MSInfo32 (we have four assigned in Hyper-V). Systems Internal Process Explorer shows 4 CPU’s as well. Dunno how this can be possible unless it’s a Hyper-V bug or the OS is displaying the wrong count. Great info on your site. Thanks – Mike

    Windows Server 2003 R2 with Service Pack 2
    Standard, Enterprise, Datacenter, and Web
    1 or 2

    • Dustin Loftis

      You can set 4 CPUs, and it’ll appear to use it, but you’ll get instability and timeshifting and all sorts of unpredictable strangeness on your 2003 guests.

  2. someshsays

    I was able to add upto 16 vCPUs.


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: