Using multiple processors in VirtualBox VMs
I noticed recently that my Ubuntu Narwhal OS running on Virtual Box was running Eclipse far slower than it should be. Ubuntu's System Monitor showed only one CPU, and it was pretty busy. My machine is an i3 processor laptop, with 4 cores. Why was Ubuntu only using one processor?
It turns out that you need to change the settings in the VM VirtualBox manager to make it use more. Right click on your VM, and choose settings. Click on system in the left hand column, and click the processor tab. Here you can choose the number of processors that the VM will use. I set mine to 4. I also chose to enable PAE/NX which allows your VM to access more than 4GB of RAM. You also need to enable the IO APIC option back on the Motherboard tab. Without this you can not use more than one processor. After making these changes your VM may now support multiple processors, or, as in my case it may refuse to boot. If your VM fails to boot as mine did, try enabling VT-x/AMD_V in your bios settings. After enabling this in my BIOS, my VM booted smoothly and my Ubuntu VM is now showing four processors in the System Monitor and running nicely.