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With VMWare it works fine and I can run multiple cores on a VMWare image. With VirtualBox I can only run 1 CPU on a image. Its annoying.

Why does Virtualbox not work the same as VMware in this respect?

My CPU is:

XEON 3.00GHz Intel 90nm 2MBCache QUAD CPU x14 Socket 604 mPGA Family 15 Model 4(04) Stepping 3 Revision 05 MMX SSE3 XD

SIV.exe tells me:

No virtual machine extensions x86 with 64-bit support
NO IA64 support
MPS but with NO MCP
2 physical processors, 2 cores, 4 logical processors

I tried manually setting my # of CPU's and it causes this error which I cannot reverse without restarting my whole computer.

C:\Program Files\Sun\VirtualBox>VBoxManage modifyvm XPSP3 --cpus 2
Sun VirtualBox Command Line Management Interface Version 3.1.4
(C) 2005-2010 Sun Microsystems, Inc.
All rights reserved.
share|improve this question
You might be better off asking Sun why they developed their product a particular way. – Zoredache Mar 18 '10 at 23:12
Superuser may be a better fit for this question IMO. – Chris Lercher Mar 18 '10 at 23:23
@chris - agreed, VirtualBox is a client-side virtualisation program – Mark Henderson Mar 18 '10 at 23:24
I disagree only because “client-side” can still be something used in the enterprise. Someone running a dual proc Xeon system is a bit less likely to be a home user as well. – David Mar 19 '10 at 0:59
@Dave, I agree but I also find it hard to decide whether to cast a close vote for it being off-topic, subject & argumentative or not a real question. – John Gardeniers Mar 19 '10 at 3:37

I don't know, if this is because of your XEON processor. I can run two cores inside VirtualBox on my Core2Duo (Host: MacOS; Guest: Linux).

Did you enable VT-x/AMD-V (in Settings/System/Acceleration)? Did you install the VirtualBox guest additions in your guest system (Devices/Install Guest Additions...)?

share|improve this answer
the Acceleration options are checked and greyed out and so I cannot change them. I couldn't find the "Devices/Install Guest Additons" thing that you refer to... – djangofan Mar 19 '10 at 20:04
The system on which I've enabled the two cores is a Ubuntu 9.10 Desktop (in contrast, my server instances all run with 1 core, so I don't know). I have no idea, what it means that your "VT-x/AMD-V" setting is grayed out - I don't remember reading anything about that in the VirtualBox documentation. But: The "Devices/Install Guest Additions" you should find in the menu (not in the settings dialog), as soon as the VM is started. Keep in mind, that I installed those on a desktop system, and I think I remember, I had problems installing them on a headless environment. But they solve many problems. – Chris Lercher Mar 19 '10 at 20:32
its version 3.14. yep, i had already installed guest additions, which from VMWare experience is one of the first things I do. doesn't make a difference as far as I can tell. – djangofan Mar 23 '10 at 21:46
Maybe these hardware virtualization extensions could be turned off in the BIOS of your PC (?) - Unfortunately I can't check this here, since my Mac doesn't have BIOS settings. – Chris Lercher Mar 23 '10 at 22:44
good idea. the bios wouldnt let me enable it. the bios just says "multiple cpu capability=no" but it says yes to hyperthreading. – djangofan Mar 23 '10 at 23:22

How do you know you can only use one CPU? When you try to create a virtual machine with more, do you get an error? What about if you use VBoxManage modifyvm and try to set the number of CPUs manually?

share|improve this answer
no error. the UI just doesn't give me the option to select more than one cpu... its greyed out. – djangofan Mar 19 '10 at 19:57
Which version of VirtualBox do you have? I believe you need at least 3.0 to do guest SMP. Also, try using the command line tools: "VBoxManage modifyvm <vmname> --cpus #" where # is the number of CPUs you want to use. – David Mar 20 '10 at 8:28
The VBoxManage thing didn't help. It changed my CPU but the VM wouldn't start, complaining about not having VT-x support or something. – djangofan Mar 23 '10 at 22:01
It sounds like VirtualBox doesn’t support multiple virtual CPUs on your processor. I know it works on all modern machines I’ve tried, but if your processor is socket 604, it’s quite old. Have you tried creating a new clean VM as a last resort? As another option, set it to a different OS like Windows 2003 instead of Windows XP. – David Mar 24 '10 at 8:30

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