How do you know if a computer can install another monitor?
I always wanted a dual monitor for multi-tasking.

Do you have another available display output on your video card?

helps to also have something better then a single core

Either you need a computer that has a video card with two display ports, or an external video card, and a onboard display on a motherboard that supports running both a GPU and MOBO Display (This is not very common, but might be the case if you have like an Asus)