18

I would like to use more than one CPU to run Ubuntu 14.04 (Trusty Tahr) 32-bit in VirtualBox, but when I stop the machine and go in Settings → System → Processor, the processor(s) slider is grayed out as you can see in the screenshot image. How can I enable this feature?

Host OS: Windows 10 Pro 64-bit
Guest OS: Ubuntu 14.04 32-bit
VirtualBox: Version 5.1.22 r115126
Processor: Intel(R) Core(TM) i7-3770 CPU @ 3.40 GHz (8 CPUs), ~3.4 GHz

Enter image description here

PS: My problem in the first instance is that the Ubuntu virtual machine is extremely slow and I would like to improve the performance, so any suggestion for that would also be welcome.

Peter Mortensen
  • 30,738
  • 21
  • 105
  • 131
Guillaume.P
  • 421
  • 1
  • 4
  • 12

7 Answers7

15

To increase performance you need to increase RAM and to use more than one CPU you need to enable "Virtualization technology" in the BIOS. Go to your BIOS options and search for "Virtualization technology" under "System settings" or similar. This is either called Intel-Vi-D or Intel-Vi with AMD processor. That name is then similar to AMD-V.

If you still have a problem with your VirtualBox not giving you an option to use multiple CPUs then you will most probably have to check if Hyper-V is installed in the "Turn Windows Features on or off". Which you might need to disable in order to use multiple CPU cores.

Some computers still might have no function towards virtualization use of multiple cores. That can be old computer models or more specific laptop computers. In some, you might need to check if there is a new BIOS version available for your computer.

Peter Mortensen
  • 30,738
  • 21
  • 105
  • 131
guest
  • 166
  • 3
  • In addition to turning off/disabling "Hyper-V" in the "Turn Windows features on or off" dialog, make sure you also turn off/disable "Windows Hypervisor Platform". I had to make sure Virtualization was enabled in BIOS, and Hyper-V and Windows Hypervisor were disabled before I could set 64-bit and multi-processor VMs. – Thomas Taylor Nov 01 '18 at 16:37
10

For me I just had to forget the saved state with a right click on the virtual device.

Stephen Rauch
  • 47,830
  • 31
  • 106
  • 135
Alan
  • 101
  • 1
  • 2
4

Please make sure that you disable the Hyper-V. Go to Control Panel → Turn Windows features on or off → Uncheck Hyper-V → Restart your computer.

Peter Mortensen
  • 30,738
  • 21
  • 105
  • 131
Lee
  • 71
  • 2
  • The solution for my problem has already been given and Hyper-V was not the problem since I activated it and it worked. The problem came from the BIOS options. – Guillaume.P Jan 24 '18 at 20:52
2

My problem is just a little bit different, but it fits the question. I can not make the guest use more than one processor.

The slider is not grayed, and I can set it to 1..4 (it is a dual core host).

But setting it on 2 and booting the Windows guest, it only sees one.

I had also tried all possible values for the slider. Windows guest always see one, not more.

If on Windows guest, I type set on a console. I always get a line with, no matter the position on the slider:

NUMBER_OF_PROCESSORS=1

I can not enable multiple CPUs on VirtualBox that guest.

The weird thing is that if I put a live CD Linux distribution ISO on that guest's virtual CD unit, it can see all the processors I set on the slider... it is just the Windows guest the one that ignores the slider... I am getting mad... and am out of ideas.

The problem occurs because when Windows was installed it was configured with only one processor, so it installed in a no multi-processor way and there is no way for it to see more than one, except re-intalling Windows, but this time with two or more on the slider, so it installs in SMP mode.

So, for anyone having the problem:

  • I can not use more than one processor on windows guest
  • I can move the slider

The answer is not going to the BIOS. The answer is:

  • Please install that Windows with the slider in 2 or more, not on just 1.

I remember I had a similar problem with an old Windows XP guest. At that time I had tried a patch to change Windows to SMP mode and a reboot, but it was so unstable, that I opted to reinstall it directly with 2 on the slider.

Peter Mortensen
  • 30,738
  • 21
  • 105
  • 131
Claudio
  • 21
  • 1
1

Looks like you have to power off the virtual machine (do not Save state)and edit those settings.

Silent E
  • 39
  • 5
  • This wasn't the problem at the time and even after reboot of the host I couldn't get it working. However enabling the virtualisation in the Bios did the trick – Guillaume.P Oct 06 '20 at 07:51
-2

Please stop and power off your VM and then drag.

It will work.

Peter Mortensen
  • 30,738
  • 21
  • 105
  • 131
Innovative ideas
  • 11
  • 1
    The question clearly stipulates that they already have stopped the VM. – Eric Aya Feb 10 '19 at 13:29
  • This wasn't the problem at the time and even after reboot of the host I couldn't get it working. However enabling the virtualisation in the Bios did the trick. – Guillaume.P Feb 11 '19 at 19:03
-5

  1. Open Virtual Box.

  2. Click the name of the virtual machine that you want to make your CPU available to, then click the "Settings" button at the top of the window.

  3. Click the "System" heading on the left side of the Settings window.

  4. Click the "Processor" tab at the top of the window.

  5. Drag the slider next to "Processor(s)" to the right until the value matches the number of processors or processor cores installed in your computer.

  6. Drag the slider next to "Execution Cap" to the right until the value reads "100." This allows VirtualBox to use all of your processor's resources.

  7. Click "OK," then double-click the virtual machine to turn it on.

VKS
  • 487
  • 2
  • 7
  • 21
  • 1
    This is what i've tried as stated in the question but the slider is grayed out (can't move it). – Guillaume.P Jun 15 '17 at 08:59
  • Using all your host processors will cripple your host which in turn makes your guest unusable. Always leave enough resources for your host machine – Dawoodjee Aug 12 '19 at 17:26