The line cards in the Cat6k. The Cat6k is Cisco's flagship product, a layer-3 switch. By itself, it's an refrigerator-sized empty chassis. Add a "SUP" card to it, which is roughly the shape of an oblong pizza box, and you have something you can run Cisco's OS on. Plug line cards into it and you have places to plug networking cables of varying types. The line cards themselves have processors and various ways of interfacing to the backplane in the chassis.