Do you know what 4k is? Well, it is super high resolution video that is about 4 times the resolution of current HD video known as 1080P. It is so new and expensive that even most theaters do not have it. So pretty much it is really cool and looks really good. This guy got a MacBookAir playing and editing 4k video over Thunderbolt (a new super high speed way to connect things to new Apple computers). The amount of data moving over the cable is ginormous. He used a "Thunderbolt expansion chassis" to hook up a Red Rocket GPU to do the fancy graphics needed to play the video. You can really add just about any pci express card to a computer with that.