The Juniper switch is the easiest to understand. Core switches are all about speed. If designed properly, the only tasks a core switch should perform are routing at Layer 3 (the network layer) and switching at Layer 2 (the data link layer that moves data across the physical links of a network).
Core switches are high-throughput, high-performance packet and frame movers. Packets and frames are simply moved from one core switch to another core switch, and eventually down to the next tier of switches -- the distribution tier.