You can increase performance of a virtual machine by making more processors available because more tasks can be performed simultaneously. When you assign a virtual processor to the virtual machine, it reduces the processor resources that are available to your Mac.

For Windows virtual machines running mostly office and Internet productivity applications, using multiple virtual processors is not beneficial, so the default single virtual processor is ideal. For server workloads and compute-intensive applications, adding extra virtual processors may provide an increase in application performance.
Application Recommended number of processors
Desktop applications 1 processor
Server operating systems 2 processors
Video encoding, modeling, and scientific 4 processors

In some circumstances, adding additional processors can decrease the overall performance of the virtual machine and your Mac. This can occur if the operating system or application is not using the processors efficiently. In this case, reducing the number of processors is recommended.

Assigning all processors on the Mac to the virtual machine results in extremely poor performance. macOS must continue to perform background tasks even if no Mac applications are running. If you assign all processors to a virtual machine, this prevents important Mac tasks from being completed.


Shut down or power off the virtual machine. You cannot change the setting while the virtual machine is powered on or suspended.


  1. Select Window > Virtual Machine Library.
  2. Select a virtual machine in the Virtual Machine Library window and click Settings.
  3. Under System Settings in the Settings window, click Processors & Memory.
  4. Select the number of processor cores for the virtual machine.
    Information about your selected number of processors is displayed at the bottom of the Processors & Memory window.
  5. Restart the virtual machine.