I have a VirtualBox VM running Windows 10 on Windows 10.

My host computer specs:

Device name _______________
Processor   Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz   1.80 GHz
Installed RAM   8.00 GB (7.88 GB usable)
Device ID               ______________________________________
Product ID  ________________________
System type 64-bit operating system, x64-based processor
Pen and touch   Pen and touch support with 10 touch points

My guest VM specs are:

  • RAM: 3040MB
  • CPU: 1 Processor
  • Execution Cap: 100%
  • GPU Memory: 256MB
  • 3D Acceleration: Enabled

I have VirtualBox’s Guest Additions installed in my guest OS. With these specs, it runs pretty smooth, but when I click buttons on the PC, it takes time to load. When I change the number of processors to 3, it got dramatically laggy.

enter image description here

How can I improve the performance of my VM?

  • The screenshot you posted from Windows booting is a common glitch of the emulated graphics card when switching resolutions. That is nothing unusual and has nothing to do with the power of the host or guest machine.
    – Robert
    Apr 21 at 16:52

When I change the # of processors to 3, it got dramatically laggy.

Guest slows with more CPUs

No, you're not doing anything wrong, and yes, adding processors will make a guest go slower. There's overhead in the CPU load needed to keep track of instructions in a multi-processor guest, and the more processors the more overhead.

Host machine (i5 8GB) is just adequate, so Guest machines will not be speedy.

Try using 2GB for the Guest machine as a test.

Check the speed of your host hard drive. 5400-rpm will be very slow for virtual machine use. A 7200-rpm drive is workable (my X230 has a 7200-rpm drive). A fast SSD will work well. My production Thinkpad has a fast drive.


The Intel® Core™ i5-8250U has 4 cores only!

Rule of thumb: NEVER assign more than half of the host's resources to a VM, be it RAM or CPU.

Your Windows VM in Virtualbox with, according to your post, Guest Additions installed and 1 or at most 2 CPUs (cores) is already running as fast as it can be. Only way to improve it is to have its file running from a faster drive. Any VM (or host OS for that matter) in a HDD will be painfully slow; it should run acceptably fast in a SATA SSD and even better in a NVME.

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