When to use X2Apic Mode?
Solution 1:
Here's some info on what APIC is.
When enabled, processor x2APIC support helps operating systems run more efficiently on high core count configurations and optimizes interrupt distribution in virtualized environments. Enabled mode only provides the support necessary to the operating system. So if you have a multiprocessor system, use virtualization and also know that the operating system that you use supports APIC, you can enable the option.
Also, press F1 to get more info. Maybe the Dell note down below would provide more info on that feature.