How many processors can I allocate to the guest?

[tomljones3]

I'm a little confused by what VirtualBox means in settings under the Processor section. Does it mean cores or physical processors?

I've got a host running Windows 2003 SP2 64 bit. It reports its processor as "8 core 2.00 GHz Intel Xeon E5405" and task manager shows 8 CPU graphs.

1. Does anyone know what physical hardware that I have? Intel's web site says that the 5405 has 4 cores and does not have hyper-threading. My guess is that my host has 2 processors and each processor has 4 cores.

2. How does this map to VirtualBox VMs? The VirtualBox manual refers to allocating cores and seems to be telling me that I could allocate up to 8 "processors" in the VM settings. However circumstantial evidence seems to indicate that the guest VM will lock up if I allocate 4 processors but will run fine with 1 processor. I am currently running a test with 2 "processors" allocated to the guest and it is running longer than it ever has before although that is hardly what I would call conclusive evidence.

[dmcgraw]

First a couple of things.

What version of VirtualBox are you running?

What is your guest OS?

In general, the most cores you should even assign to the guest is one less than the total number of physical cores you have in the system. When counting physical cores on the host, you should NOT count hyper-threading, which you said that your CPU does not have.

So since your host seems to have 8 physical cores, 7 should be the most you would ever assign to a guest. But again, it depends on the guest OS.

[tomljones3]

Thanks for the quick reply. The manual seemed to be pretty clear that VirtualBox was referring to physical cores.
My host OS is: Windows Server 2003 R2 Enterprise x64 Edition with SP2
My guest OS is: Windows Server 2008 Enterprise with SP2
I'm using the latest version of VirtualBox, 3.2.8 r64453

Initially I created a new VM with 4 "processors" and installed Win 2008. It installed OK, but as soon as I tried to run Windows Update the guest locked up and started using 50% of the host processor. This would happen anytime the guest started using a high processor load. I set the guest to have 1 processor and it runs perfectly. Now I have it set to 2 processors and it seems to be running fine. This is what got me confused about what VirtualBox meant by "processor" on the guest.

I will continue to experiment with some of the other settings to try and determine what the source of the problem is. The VirtualBox log does not have any entries during the time the guest is locked up.