I set 2 CPU on virtualbox xp and boot successfully.
But when I use speccy to check.
It says I only have 1 cpu and only 1 core.
How do I enable the second CPU?
For Windows 64-bit guest and if you want to use more than 1 CPU in your guest we need to enable I/O APIC prior to installing Windows.
This can be done in the System -> Motherboard setting in the VirtualBox Manager.
Note: These setting has to be made before installing Windows as only then Windows will be installed with the appropriate kernel.