We help IT Professionals succeed at work.

Why does my server 2003 guest only see 1 processor core on a Core i5 Ubuntu 11.04 host system?

I have a server setup with Ubuntu 11.04 running the latest version of Virtualbox 4.1.4.  The server has 4gigs of ram and a Core i5 processor with 4 cores.  I have a guest system setup with Windows Server 2003.  I have setup the guest system with 2gb ram and access to all 4 cores.  When I load the os up, the task manager only reports one processor core.  But the virtual machine status shows that it is giving access to all 4 cores.  Is there some sort of limitation in Windows server 2003 that would prevent me from seeing all 4 cores?
Watch Question

Lee W, MVPTechnology and Business Process Advisor
Most Valuable Expert 2013

Yes and no.

Yes there is a limitation in 2003 that prevents you from seeing all four cores - Standard edition (IF I REMEMBER CORRECTLY) will only see two physical processors.  When a Windows OS is run virtually, it cannot "differentiate" cores from physical processors so it assumes EVERYTHING is a physical processor.  (This is due to the way the Virtualization service presents the CPUs to the guest OS)  

That said, I MIGHT be misremembering and the limit may be 4 processors not 2 (as I think about it, I'm probably misremembering - but in either case, add a second processor and/or a better processor with more cores and you won't be able to use them on the single guest Windows Server Standard VM).

Now, that said, I suspect one of two things:

1.  Simple: you have task manager set to display all four CPUs as one graph; or
2.  You have the Uniprocessor kernel loaded which can only see one processor.  You can upgrade this to the multi-processor kernel fairly easy - you go into device manager and under "Processors" (or CPUs, I don't have a 2003 box in front of me to reference), you right click and look for a place to "upgrade" or "Update" the driver and then select from the list the multi processor kernel.  Then reboot.

(I'd recommend taking a snapshot as a backup first, just to be safe if it's #2).
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Expert of the Year 2017

have you allocated 4vCPUs to the virtual machine?
VMware and Virtualization Consultant
Expert of the Year 2017
Server 2003 Standard supports 2 or 4-Way Symmetric Multiprocessing.
Server 2003 Enterprise supports 8-Way Symmetric Multiprocessing.

 Uniprocessor HAL
1. Right Click,
2. ACPI Uniprocessor PC,
3. Update Driver,
4. Select No,
5. Next,
6. Advanced,
7. Next,
8. Don't Search,
9. ACPI Multiprocessor PC,
10. Finish  
11. Restart VM

See here for Comparisons of versions and included features


I figured it had something to do with the processor drivers.  Under device manager, under computer it had some sort of acpi driver but it was not uniprocessor or multiprocessor.   I updated the driver to acpi multiprocessor.  Just waiting for a time when I can reboot it.  But I think this is the problem.  I will award the points after I verify that it is working.  Thanks.


Sorry for not paying attention to this.  I finally noticed I had an open question that needed to be closed.  Yes this did work with a few work a rounds.  I even had to do it on another pc as well that was not a virtual system.  Thanks.

Explore More ContentExplore courses, solutions, and other research materials related to this topic.