Choosing the number of processors

[Paul Abrahams]

VBox has, of course, the ability to set the number of processors in the virtual machine. But how do you make an intelligent choice? Should the number of processors in the virtual machine be the same as in the host? What are the consequences if it isn't?

[frank]

The best choice is to select as view guest processors as possible. The more guest processor you enable the more overhead is induced. So if you have a usual guest which would always never induce a load bigger than 1, there is no point adding more than one guest CPU to your guest. More than one guest CPU makes only sense if you have a guest which makes heavily use of the cores (e.g. frequent compilation jobs) AND if your host is idle enough to serve all virtual processors. Note that with 2 host cores the host is often not idle as the VMM itself needs processor cycles as well as emulating the I/O devices.

[Paul Abrahams]

This would be very useful information to put into the FAQ or even into the user guide if it isn't already hiding somewhere there.