What is Cisco Supervisor Engine?

Supervisor Engine is a module that is installed in the Cisco Chassis-based Catalyst Switches or Routers. Supervisor engine contains nearly all the same components of a fixed Cisco Switches or Routers. These Supervisor engines come in a variety of different types with different functionalities and are installed in the Switches/Router Chassis as per requirements of the network types.

Benefits of Supervisor Engines
By installing Latest Supervisor Engines in your existing investments (Switches and Routers) you can scale system performance and integrate next-generation services into your Networks.
Within a single multilayer switch chassis, two supervisor modules with integrated route processors can be used to provide hardware redundancy. If an entire supervisor module fails, the other module can pick up the pieces and continue operating the switch.
The supervisor engine contains the following integrated daughter cards that perform forwarding and routing and provide the protocols supported on the router.

Cisco Supervisor Engine, Sup-2T

Policy Feature Card (PFC) is the forwarding plane and does the following:

Performs Layer 2 and Layer 3 forwarding.
Enforces access control list (ACL) functions.
Performs policing and marking for quality of service (QoS) traffic.

Multilayer Switch Feature Card (MSFC) is the control plane and does the following:
Performs routing for the chassis. The MSFC contains the route processor (RP) and Switch processor (SP) for the router.
Runs Layer 2 and Layer 3 protocols, such as the Spanning Tree Protocol (STP) and others.

You can View a 3D model of Catalyst 6500 Switch, here you can see how the Catalyst Switch 6500 looks like, Mount/Demount Supervisor engines, and other inserted modules, view short details of them by demounting from Chassis.