They're not different computers. Most likely he has a triple monitor setup(or is it a quad?), like 3 monitors on the same pc and you can swing apps between them and shiz. If you are a gamer it's nice to have more than one monitor as you can have a site opened on one of them while playing on another one.
I have 2 monitors as well, not enough space nor money to get a third one so for now it has to suffice.