[Resolved] How to enable additional cores after creating VM

[TomG]

I'm new to VMs, just installed VirtualBox the other day and have it working well on Win10 PC, i7-8700K with 64 Gb RAM. I created one VM, also Win10. There is only one core available, and when I try to assign more cores, the slider is grayed out. Is there any way to do this after creating a VM Guest?

[socratis]

Is there any way to do this after creating a VM Guest?

Sure. As long as you don't try to change the hardware while the VM is running, saved or paused, but completely shut down (from within the VM). You wouldn't change the number (or the kind) of CPUs on your real computer while it was up and running, would you?

Just remember to not assign more cores than you have on your host minus 1. So, if you have 6 cores, don't give any more than 5 to your VM, or your host will starve. And mind you, I'm talking about cores, not threads. According to Intel your i7-8700K has 6 cores/12 threads. So, no more than 5 CPUs to the VM.

If in doubt, post a ZIPPED VM log:

• Start the VM from cold-boot (not from a paused or saved state) / Login / Shutdown the VM.
• With the VM completely shut down (not paused or saved), right-click on the VM in the VirtualBox Manager and select "Show Log".
• Save only the first "VBox.log", ZIP it and attach it to your response. See the "Upload attachment" tab below the reply form.

[TomG]

Perfect! Thanks so much—it's so obvious that the machine would have to be shut down to make the changes, but it never occurred to me. I appreciate the help!

[socratis]

Glad you got it going. Marking as [Resolved].